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@ -3,47 +3,47 @@ Compiler
The ARTIQ compiler transforms the Python code of the kernels into machine code executable on the core device. For limited purposes (normally, obtaining executable binaries of idle and startup kernels), it can be accessed through :mod:`~artiq.frontend.artiq_compile`. Otherwise it is invoked automatically whenever a function with an applicable decorator is called. The ARTIQ compiler transforms the Python code of the kernels into machine code executable on the core device. For limited purposes (normally, obtaining executable binaries of idle and startup kernels), it can be accessed through :mod:`~artiq.frontend.artiq_compile`. Otherwise it is invoked automatically whenever a function with an applicable decorator is called.
ARTIQ kernel code accepts *nearly,* but not quite, a strict subset of Python 3. The necessities of real-time operation impose a harsher set of limitations; as a result, many Python features are necessarily omitted, and there are some specific discrepancies (see also :ref:`compiler-pitfalls`). ARTIQ kernel code accepts *nearly,* but not quite, a strict subset of Python 3. The necessities of real-time operation impose a harsher set of limitations; as a result, many Python features are necessarily omitted, and there are some specific discrepancies (see also :ref:`compiler-pitfalls`).
In general, ARTIQ Python supports only statically typed variables; it implements no heap allocation or garbage collection systems, essentially disallowing any heap-based data structures (although lists and arrays remain available in a stack-based form); and it cannot use runtime dispatch, meaning that, for example, all elements of an array must be of the same type. Nonetheless, technical details aside, a basic knowledge of Python is entirely sufficient to write useful and coherent ARTIQ experiments. In general, ARTIQ Python supports only statically typed variables; it implements no heap allocation or garbage collection systems, essentially disallowing any heap-based data structures (although lists and arrays remain available in a stack-based form); and it cannot use runtime dispatch, meaning that, for example, all elements of an array must be of the same type. Nonetheless, technical details aside, a basic knowledge of Python is entirely sufficient to write useful and coherent ARTIQ experiments.
.. note:: .. note::
The ARTIQ compiler is now in its second iteration. The third generation, known as NAC3, is `currently in development <https://git.m-labs.hk/M-Labs/nac3>`_, and available for pre-alpha experimental use. NAC3 represents a major overhaul of ARTIQ compilation, and will feature much faster compilation speeds, a greatly improved type system, and more predictable and transparent operation. It is compatible with ARTIQ firmware starting at ARTIQ-7. Instructions for installation and basic usage differences can also be found `on the M-Labs Forum <https://forum.m-labs.hk/d/392-nac3-new-artiq-compiler-3-prealpha-release>`_. While NAC3 is a work in progress and many important features remain unimplemented, installation and feedback is welcomed. The ARTIQ compiler is now in its second iteration. The third generation, known as NAC3, is `currently in development <https://git.m-labs.hk/M-Labs/nac3>`_, and available for pre-alpha experimental use. NAC3 represents a major overhaul of ARTIQ compilation, and will feature much faster compilation speeds, a greatly improved type system, and more predictable and transparent operation. It is compatible with ARTIQ firmware starting at ARTIQ-7. Instructions for installation and basic usage differences can also be found `on the M-Labs Forum <https://forum.m-labs.hk/d/392-nac3-new-artiq-compiler-3-prealpha-release>`_. While NAC3 is a work in progress and many important features remain unimplemented, installation and feedback is welcomed.
ARTIQ Python code ARTIQ Python code
----------------- -----------------
A variety of short experiments can be found in the subfolders of ``artiq/examples``, especially under ``kc705_nist_clock/repository`` and ``no_hardware/repository``. Reading through these will give you a general idea of what ARTIQ Python is capable of and how to use it. A variety of short experiments can be found in the subfolders of ``artiq/examples``, especially under ``kc705_nist_clock/repository`` and ``no_hardware/repository``. Reading through these will give you a general idea of what ARTIQ Python is capable of and how to use it.
Functions and decorators Functions and decorators
^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^
The ARTIQ compiler recognizes several specialized decorators, which determine the way the decorated function will be compiled and handled. The ARTIQ compiler recognizes several specialized decorators, which determine the way the decorated function will be compiled and handled.
``@kernel`` (see :meth:`~artiq.language.core.kernel`) designates kernel functions, which will be compiled for and wholly executed on the core device; the basic setup and background for kernels is detailed on the :doc:`getting_started_core` page. ``@subkernel`` (:meth:`~artiq.language.core.subkernel`) designates subkernel functions, which are largely similar to kernels except that they are executed on satellite devices in a DRTIO setting, with some associated limitations; they are described in more detail on the :doc:`using_drtio_subkernels` page. ``@kernel`` (see :meth:`~artiq.language.core.kernel`) designates kernel functions, which will be compiled for and wholly executed on the core device; the basic setup and background for kernels is detailed on the :doc:`getting_started_core` page. ``@subkernel`` (:meth:`~artiq.language.core.subkernel`) designates subkernel functions, which are largely similar to kernels except that they are executed on satellite devices in a DRTIO setting, with some associated limitations; they are described in more detail on the :doc:`using_drtio_subkernels` page.
``@rpc`` (:meth:`~artiq.language.core.rpc`) designates functions to be executed on the host machine, which are compiled and run in regular Python, outside of the core device's real-time limitations. Notably, functions without decorators are assumed to be host-bound by default, and treated identically to an explicitly marked ``@rpc``. As a result, the explicit decorator is only really necessary when specifying additional flags (for example, ``flags={"async"}``, see below). ``@rpc`` (:meth:`~artiq.language.core.rpc`) designates functions to be executed on the host machine, which are compiled and run in regular Python, outside of the core device's real-time limitations. Notably, functions without decorators are assumed to be host-bound by default, and treated identically to an explicitly marked ``@rpc``. As a result, the explicit decorator is only really necessary when specifying additional flags (for example, ``flags={"async"}``, see below).
``@portable`` (:meth:`~artiq.language.core.portable`) designates functions to be executed *on the same device they are called.* In other words, when called from a kernel, a portable is executed as a kernel; when called from a subkernel, it is executed as a kernel, on the same satellite device as the calling subkernel; when called from a host function, it is executed on the host machine. ``@portable`` (:meth:`~artiq.language.core.portable`) designates functions to be executed *on the same device they are called.* In other words, when called from a kernel, a portable is executed as a kernel; when called from a subkernel, it is executed as a kernel, on the same satellite device as the calling subkernel; when called from a host function, it is executed on the host machine.
``@host_only`` (:meth:`~artiq.language.core.host_only`) functions are executed fully on the host, similarly to ``@rpc``, but calling them from a kernel as an RPC will be refused by the compiler. It can be used to mark functions which should only ever be called by the host. ``@host_only`` (:meth:`~artiq.language.core.host_only`) functions are executed fully on the host, similarly to ``@rpc``, but calling them from a kernel as an RPC will be refused by the compiler. It can be used to mark functions which should only ever be called by the host.
.. warning:: .. warning::
ARTIQ goes to some lengths to cache code used in experiments correctly, so that experiments run according to the state of the code when they were started, even if the source is changed during the run time. Python itself annoyingly fails to implement this (see also `issue #416 <https://github.com/m-labs/artiq/issues/416>`_), necessitating a workaround on ARTIQ's part. One particular downstream limitation is that the ARTIQ compiler is unable to recognize decorators with path prefixes, i.e.: :: ARTIQ goes to some lengths to cache code used in experiments correctly, so that experiments run according to the state of the code when they were started, even if the source is changed during the run time. Python itself annoyingly fails to implement this (see also `issue #416 <https://github.com/m-labs/artiq/issues/416>`_), necessitating a workaround on ARTIQ's part. One particular downstream limitation is that the ARTIQ compiler is unable to recognize decorators with path prefixes, i.e.: ::
import artiq.experiment as aq import artiq.experiment as aq
[...] [...]
@aq.kernel @aq.kernel
def run(self): def run(self):
pass pass
will fail to compile. As long as ``from artiq.experiment import *`` is used as in the examples, this is never an issue. If prefixes are strongly preferred, a possible workaround is to import decorators separately, as e.g. ``from artiq.language.core import kernel``.
.. _compiler-types: will fail to compile. As long as ``from artiq.experiment import *`` is used as in the examples, this is never an issue. If prefixes are strongly preferred, a possible workaround is to import decorators separately, as e.g. ``from artiq.language.core import kernel``.
ARTIQ types .. _compiler-types:
ARTIQ types
^^^^^^^^^^^ ^^^^^^^^^^^
Python/NumPy types correspond to ARTIQ types as follows: Python/NumPy types correspond to ARTIQ types as follows:
@ -76,16 +76,16 @@ Python/NumPy types correspond to ARTIQ types as follows:
| numpy.int64 | TInt64 | | numpy.int64 | TInt64 |
+---------------+-------------------------+ +---------------+-------------------------+
| numpy.float64 | TFloat | | numpy.float64 | TFloat |
+---------------+-------------------------+ +---------------+-------------------------+
Integers are 32-bit by default but may be converted to 64-bit with ``numpy.int64``. Integers are 32-bit by default but may be converted to 64-bit with ``numpy.int64``.
The ARTIQ compiler can be thought of as overriding all built-in Python types, and types in kernel code cannot always be assumed to behave as they would in host Python. In particular, normally heap-allocated types such as arrays, lists, and strings are very limited in what they support. Strings must be constant and lists and arrays must be of constant size. Methods like ``append``, ``push``, and ``pop`` are unavailable as a matter of principle, and will not compile. Certain types, notably dictionaries, have no ARTIQ implementation and cannot be used in kernels at all. The ARTIQ compiler can be thought of as overriding all built-in Python types, and types in kernel code cannot always be assumed to behave as they would in host Python. In particular, normally heap-allocated types such as arrays, lists, and strings are very limited in what they support. Strings must be constant and lists and arrays must be of constant size. Methods like ``append``, ``push``, and ``pop`` are unavailable as a matter of principle, and will not compile. Certain types, notably dictionaries, have no ARTIQ implementation and cannot be used in kernels at all.
.. tip:: .. tip::
Instead of pushing or appending, preallocate for the maximum number of elements you expect with a list comprehension, i.e. ``x = [0 for _ in range(1024)]``, and then keep a variable ``n`` noting the last filled element of the array. Afterwards, ``x[0:n]`` will give you a list with that number of elements. Instead of pushing or appending, preallocate for the maximum number of elements you expect with a list comprehension, i.e. ``x = [0 for _ in range(1024)]``, and then keep a variable ``n`` noting the last filled element of the array. Afterwards, ``x[0:n]`` will give you a list with that number of elements.
Multidimensional arrays are allowed (using NumPy syntax). Element-wise operations (e.g. ``+``, ``/``), matrix multiplication (``@``) and multidimensional indexing are supported; slices and views (currently) are not. Multidimensional arrays are allowed (using NumPy syntax). Element-wise operations (e.g. ``+``, ``/``), matrix multiplication (``@``) and multidimensional indexing are supported; slices and views (currently) are not.
User-defined classes are supported, provided their attributes are of other supported types (attributes that are not used in the kernel are ignored and thus unrestricted). When several instances of a user-defined class are referenced from the same kernel, every attribute must have the same type in every instance of the class. User-defined classes are supported, provided their attributes are of other supported types (attributes that are not used in the kernel are ignored and thus unrestricted). When several instances of a user-defined class are referenced from the same kernel, every attribute must have the same type in every instance of the class.
@ -99,11 +99,11 @@ Kernel code can call host functions without any additional ceremony. However, su
def return_four() -> TInt32: def return_four() -> TInt32:
return 4 return 4
Kernels can freely modify attributes of objects shared with the host. However, by necessity, these modifications are actually applied to local copies of the objects, as the latency of immediate writeback would be unsupportable in a real-time environment. Instead, modifications are written back *when the kernel completes;* notably, this means RPCs called by a kernel itself will only have access to the unmodified host version of the object, as the kernel hasn't finished execution yet. In some cases, accessing data on the host is better handled by calling RPCs specifically to make the desired modifications. Kernels can freely modify attributes of objects shared with the host. However, by necessity, these modifications are actually applied to local copies of the objects, as the latency of immediate writeback would be unsupportable in a real-time environment. Instead, modifications are written back *when the kernel completes;* notably, this means RPCs called by a kernel itself will only have access to the unmodified host version of the object, as the kernel hasn't finished execution yet. In some cases, accessing data on the host is better handled by calling RPCs specifically to make the desired modifications.
.. warning:: .. warning::
Kernels *cannot and should not* return lists, arrays, or strings they have created, or any objects containing them; in the absence of a heap, the way these values are allocated means they cannot outlive the kernels they are created in. Trying to do so will normally be discovered by lifetime tracking and result in compilation errors, but in certain cases lifetime tracking will fail to detect a problem and experiments will encounter memory corruption at runtime. For example: :: Kernels *cannot and should not* return lists, arrays, or strings they have created, or any objects containing them; in the absence of a heap, the way these values are allocated means they cannot outlive the kernels they are created in. Trying to do so will normally be discovered by lifetime tracking and result in compilation errors, but in certain cases lifetime tracking will fail to detect a problem and experiments will encounter memory corruption at runtime. For example: ::
def func(a): def func(a):
return a return a
@ -117,44 +117,44 @@ Kernels can freely modify attributes of objects shared with the host. However, b
# results in memory corruption # results in memory corruption
return func([1, 2, 3]) return func([1, 2, 3])
will compile, **but corrupts at runtime.** On the other hand, lists, arrays, or strings can and should be used as inputs for RPCs, and this is the preferred method of returning data to the host. In this way the data is inherently read and sent before the kernel completes and there are no allocation issues. will compile, **but corrupts at runtime.** On the other hand, lists, arrays, or strings can and should be used as inputs for RPCs, and this is the preferred method of returning data to the host. In this way the data is inherently read and sent before the kernel completes and there are no allocation issues.
Available built-in functions Available built-in functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ARTIQ makes various useful built-in and mathematical functions from Python, NumPy, and SciPy available in kernel code. They are not guaranteed to be perfectly equivalent to their host namesakes (for example, ``numpy.rint()`` normally rounds-to-even, but in kernel code rounds toward zero) but their behavior should be basically predictable. ARTIQ makes various useful built-in and mathematical functions from Python, NumPy, and SciPy available in kernel code. They are not guaranteed to be perfectly equivalent to their host namesakes (for example, ``numpy.rint()`` normally rounds-to-even, but in kernel code rounds toward zero) but their behavior should be basically predictable.
.. list-table:: .. list-table::
:header-rows: 1 :header-rows: 1
+ * Reference + * Reference
* Functions * Functions
+ * `Python built-ins <https://docs.python.org/3/library/functions.html>`_ + * `Python built-ins <https://docs.python.org/3/library/functions.html>`_
* - ``len()``, ``round()``, ``abs()``, ``min()``, ``max()`` * - ``len()``, ``round()``, ``abs()``, ``min()``, ``max()``
- ``print()`` (with caveats; see below) - ``print()`` (with caveats; see below)
- all basic type conversions (``int()``, ``float()`` etc.) - all basic type conversions (``int()``, ``float()`` etc.)
+ * `NumPy mathematic utilities <https://numpy.org/doc/stable/reference/routines.math.html>`_ + * `NumPy mathematic utilities <https://numpy.org/doc/stable/reference/routines.math.html>`_
* - ``sqrt()``, ``cbrt``` * - ``sqrt()``, ``cbrt```
- ``fabs()``, ``fmax()``, ``fmin()`` - ``fabs()``, ``fmax()``, ``fmin()``
- ``floor()``, ``ceil()``, ``trunc()``, ``rint()`` - ``floor()``, ``ceil()``, ``trunc()``, ``rint()``
+ * `NumPy exponents and logarithms <https://numpy.org/doc/stable/reference/routines.math.html#exponents-and-logarithms>`_ + * `NumPy exponents and logarithms <https://numpy.org/doc/stable/reference/routines.math.html#exponents-and-logarithms>`_
* - ``exp()``, ``exp2()``, ``expm1()`` * - ``exp()``, ``exp2()``, ``expm1()``
- ``log()``, ``log2()``, ``log10()`` - ``log()``, ``log2()``, ``log10()``
+ * `NumPy trigonometric and hyperbolic functions <https://numpy.org/doc/stable/reference/routines.math.html#trigonometric-functions>`_ + * `NumPy trigonometric and hyperbolic functions <https://numpy.org/doc/stable/reference/routines.math.html#trigonometric-functions>`_
* - ``sin()``, ``cos()``, ``tan()``, * - ``sin()``, ``cos()``, ``tan()``,
- ``arcsin()``, ``arccos()``, ``arctan()`` - ``arcsin()``, ``arccos()``, ``arctan()``
- ``sinh()``, ``cosh()``, ``tanh()`` - ``sinh()``, ``cosh()``, ``tanh()``
- ``arcsinh()``, ``arccosh()``, ``arctanh()`` - ``arcsinh()``, ``arccosh()``, ``arctanh()``
- ``hypot()``, ``arctan2()`` - ``hypot()``, ``arctan2()``
+ * `NumPy floating point routines <https://numpy.org/doc/stable/reference/routines.math.html#floating-point-routines>`_ + * `NumPy floating point routines <https://numpy.org/doc/stable/reference/routines.math.html#floating-point-routines>`_
* - ``copysign()``, ``nextafter()`` * - ``copysign()``, ``nextafter()``
+ * `SciPy special functions <https://docs.scipy.org/doc/scipy/reference/special.html>`_ + * `SciPy special functions <https://docs.scipy.org/doc/scipy/reference/special.html>`_
* - ``erf()``, ``erfc()`` * - ``erf()``, ``erfc()``
- ``gamma()``, ``gammaln()`` - ``gamma()``, ``gammaln()``
- ``j0()``, ``j1()``, ``y0()``, ``y1()`` - ``j0()``, ``j1()``, ``y0()``, ``y1()``
Basic NumPy array handling (``np.array()``, ``numpy.transpose()``, ``numpy.full``, ``@``, element-wise operation, etc.) is also available. NumPy functions are implicitly broadcast when applied to arrays. Basic NumPy array handling (``np.array()``, ``numpy.transpose()``, ``numpy.full``, ``@``, element-wise operation, etc.) is also available. NumPy functions are implicitly broadcast when applied to arrays.
Print and logging functions Print and logging functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -163,7 +163,7 @@ ARTIQ offers two native built-in logging functions: ``rtio_log()``, as presented
``print()`` itself is in practice an RPC to the regular host Python ``print()``, i.e. with output either in the terminal of :mod:`~artiq.frontend.artiq_run` or in the client logs when using :mod:`~artiq.frontend.artiq_dashboard` or :mod:`~artiq.frontend.artiq_compile`. This means on one hand that it should not be used in idle, startup, or subkernels, and on the other hand that it suffers of some of the timing limitations of any other RPC, especially if the RPC queue is full. Accordingly, it is important to be aware that the timing of ``print()`` outputs can't reliably be used to debug timing in kernels, and especially not the timing of other RPCs. ``print()`` itself is in practice an RPC to the regular host Python ``print()``, i.e. with output either in the terminal of :mod:`~artiq.frontend.artiq_run` or in the client logs when using :mod:`~artiq.frontend.artiq_dashboard` or :mod:`~artiq.frontend.artiq_compile`. This means on one hand that it should not be used in idle, startup, or subkernels, and on the other hand that it suffers of some of the timing limitations of any other RPC, especially if the RPC queue is full. Accordingly, it is important to be aware that the timing of ``print()`` outputs can't reliably be used to debug timing in kernels, and especially not the timing of other RPCs.
.. _compiler-pitfalls: .. _compiler-pitfalls:
Pitfalls Pitfalls
-------- --------

20
doc/manual/getting_started_core.rst
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@ -100,19 +100,11 @@ Create a new file ``rtio.py`` containing the following: ::
delay(2*us) delay(2*us)
self.ttl0.pulse(2*us) self.ttl0.pulse(2*us)
In its :meth:`~artiq.language.environment.HasEnvironment.build` method, the experiment obtains the core device and a TTL device called ``ttl0`` as defined in the device database. In its :meth:`~artiq.language.environment.HasEnvironment.build` method, the experiment obtains the core device and a TTL device called ``ttl0`` as defined in the device database. In ARTIQ, TTL is used roughly synonymous with "a single generic digital signal" and does not refer to a specific signaling standard or voltage/current levels.
In ARTIQ, TTL is used roughly synonymous with "a single generic digital signal" and does not refer to a specific signaling standard or voltage/current levels.
When :meth:`~artiq.language.environment.Experiment.run`, the experiment first ensures that ``ttl0`` is in output mode and actively driving the device it is connected to. When :meth:`~artiq.language.environment.Experiment.run`, the experiment first ensures that ``ttl0`` is in output mode and actively driving the device it is connected to.Bidirectional TTL channels (i.e. :class:`~artiq.coredevice.ttl.TTLInOut`) are in input (high impedance) mode by default, output-only TTL channels (:class:`~artiq.coredevice.ttl.TTLOut`) are always in output mode. There are no input-only TTL channels.
Bidirectional TTL channels (i.e. :class:`~artiq.coredevice.ttl.TTLInOut`) are in input (high impedance) mode by default, output-only TTL channels (:class:`~artiq.coredevice.ttl.TTLOut`) are always in output mode.
There are no input-only TTL channels.
The experiment then drives one million 2 µs long pulses separated by 2 µs each. The experiment then drives one million 2 µs long pulses separated by 2 µs each. Connect an oscilloscope or logic analyzer to TTL0 and run ``artiq_run rtio.py``. Notice that the generated signal's period is precisely 4 µs, and that it has a duty cycle of precisely 50%. This is not what one would expect if the delay and the pulse were implemented with register-based general purpose input output (GPIO) that is CPU-controlled. The signal's period would depend on CPU speed, and overhead from the loop, memory management, function calls, etc., all of which are hard to predict and variable. Any asymmetry in the overhead would manifest itself in a distorted and variable duty cycle.
Connect an oscilloscope or logic analyzer to TTL0 and run ``artiq_run rtio.py``.
Notice that the generated signal's period is precisely 4 µs, and that it has a duty cycle of precisely 50%.
This is not what one would expect if the delay and the pulse were implemented with register-based general purpose input output (GPIO) that is CPU-controlled.
The signal's period would depend on CPU speed, and overhead from the loop, memory management, function calls, etc., all of which are hard to predict and variable.
Any asymmetry in the overhead would manifest itself in a distorted and variable duty cycle.
Instead, inside the core device, output timing is generated by the gateware and the CPU only programs switching commands with certain timestamps that the CPU computes. Instead, inside the core device, output timing is generated by the gateware and the CPU only programs switching commands with certain timestamps that the CPU computes.
@ -166,11 +158,7 @@ Try the following code and observe the generated pulses on a 2-channel oscillosc
self.ttl1.pulse(4*us) self.ttl1.pulse(4*us)
delay(4*us) delay(4*us)
ARTIQ can implement ``with parallel`` blocks without having to resort to any of the typical parallel processing approaches. ARTIQ can implement ``with parallel`` blocks without having to resort to any of the typical parallel processing approaches. It simply remembers its position on the timeline (``now_mu``) when entering the ``parallel`` block and resets to that position after each individual statement. At the end of the block, the cursor is advanced to the furthest position it reached during the block. In other words, the statements in a ``parallel`` block are actually executed sequentially. Only the RTIO events generated by the statements are *scheduled* in parallel.
It simply remembers its position on the timeline (``now_mu``) when entering the ``parallel`` block and resets to that position after each individual statement.
At the end of the block, the cursor is advanced to the furthest position it reached during the block.
In other words, the statements in a ``parallel`` block are actually executed sequentially.
Only the RTIO events generated by the statements are *scheduled* in parallel.
Remember that while ``now_mu`` resets at the beginning of each statement in a ``parallel`` block, the wall clock advances regardless. If a particular statement takes a long time to execute (which is different from -- and unrelated to! -- the events *scheduled* by the statement taking a long time), the wall clock may advance past the reset value, putting any subsequent statements inside the block into a situation of negative slack (i.e., resulting in :exc:`~artiq.coredevice.exceptions.RTIOUnderflow` ). Sometimes underflows may be avoided simply by reordering statements within the parallel block. This especially applies to input methods, which generally necessarily block CPU progress until the wall clock has caught up to or overtaken the cursor. Remember that while ``now_mu`` resets at the beginning of each statement in a ``parallel`` block, the wall clock advances regardless. If a particular statement takes a long time to execute (which is different from -- and unrelated to! -- the events *scheduled* by the statement taking a long time), the wall clock may advance past the reset value, putting any subsequent statements inside the block into a situation of negative slack (i.e., resulting in :exc:`~artiq.coredevice.exceptions.RTIOUnderflow` ). Sometimes underflows may be avoided simply by reordering statements within the parallel block. This especially applies to input methods, which generally necessarily block CPU progress until the wall clock has caught up to or overtaken the cursor.

28
doc/manual/installing.rst
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@ -6,20 +6,20 @@ ARTIQ can be installed using the Nix (on Linux) or MSYS2 (on Windows) package ma
Installing via Nix (Linux) Installing via Nix (Linux)
-------------------------- --------------------------
First install the Nix package manager. Some distributions provide a package for it; otherwise, it can be installed via the script on the `Nix website <http://nixos.org/nix/>`_. Make sure you get Nix version 2.4 or higher. Prefer a single-user installation for simplicity. First install the Nix package manager. Some distributions provide a package for it; otherwise, it can be installed via the script on the `Nix website <http://nixos.org/nix/>`_. Make sure you get Nix version 2.4 or higher. Prefer a single-user installation for simplicity.
Once Nix is installed, enable flakes, for example by running: :: Once Nix is installed, enable flakes, for example by running: ::
$ mkdir -p ~/.config/nix $ mkdir -p ~/.config/nix
$ echo "experimental-features = nix-command flakes" >> ~/.config/nix/nix.conf $ echo "experimental-features = nix-command flakes" >> ~/.config/nix/nix.conf
See also the different options for enabling flakes on `the NixOS wiki <https://nixos.wiki/wiki/flakes>`_. See also the different options for enabling flakes on `the NixOS wiki <https://nixos.wiki/wiki/flakes>`_.
The easiest way to obtain ARTIQ is to install it into the user environment with :: The easiest way to obtain ARTIQ is to install it into the user environment with ::
$ nix profile install git+https://github.com/m-labs/artiq.git $ nix profile install git+https://github.com/m-labs/artiq.git
Answer "Yes" to the questions about setting Nix configuration options (for more details see 'Troubleshooting' below.) You should now have a minimal installation of ARTIQ, where the usual front-end commands (:mod:`~artiq.frontend.artiq_run`, :mod:`~artiq.frontend.artiq_master`, :mod:`~artiq.frontend.artiq_dashboard`, etc.) are all available to you. Answer "Yes" to the questions about setting Nix configuration options (for more details see 'Troubleshooting' below.) You should now have a minimal installation of ARTIQ, where the usual front-end commands (:mod:`~artiq.frontend.artiq_run`, :mod:`~artiq.frontend.artiq_master`, :mod:`~artiq.frontend.artiq_dashboard`, etc.) are all available to you.
This installation is however quite limited, as Nix creates a dedicated Python environment for the ARTIQ commands alone. This means that other useful Python packages, which ARTIQ is not dependent on but which you may want to use in your experiments (pandas, matplotlib...), are not available. This installation is however quite limited, as Nix creates a dedicated Python environment for the ARTIQ commands alone. This means that other useful Python packages, which ARTIQ is not dependent on but which you may want to use in your experiments (pandas, matplotlib...), are not available.
@ -58,9 +58,9 @@ Installing multiple packages and making them visible to the ARTIQ commands requi
#ps.bokeh #ps.bokeh
#ps.cirq #ps.cirq
#ps.qiskit #ps.qiskit
# Note that NixOS also provides packages ps.numpy and ps.scipy, but it is # Note that NixOS also provides packages ps.numpy and ps.scipy, but it is
# not necessary to explicitly add these, since they are dependencies of # not necessary to explicitly add these, since they are dependencies of
# ARTIQ and available with an ARTIQ install anyway. # ARTIQ and available with an ARTIQ install anyway.
])) ]))
#artiq.korad_ka3005p #artiq.korad_ka3005p
#artiq.novatech409b #artiq.novatech409b
@ -83,9 +83,9 @@ Installing multiple packages and making them visible to the ARTIQ commands requi
} }
.. note:: .. note::
You might consider adding matplotlib and numba in particular, as these are required by certain ARTIQ example experiments. You might consider adding matplotlib and numba in particular, as these are required by certain ARTIQ example experiments.
You can now spawn a shell containing these packages by running ``$ nix shell`` in the directory containing the ``flake.nix``. This should make both the ARTIQ commands and all the additional packages available to you. You can exit the shell with Control+D or with the command ``exit``. A first execution of ``$ nix shell`` may take some time, but for any future repetitions Nix will use cached packages and startup should be much faster. You can now spawn a shell containing these packages by running ``$ nix shell`` in the directory containing the ``flake.nix``. This should make both the ARTIQ commands and all the additional packages available to you. You can exit the shell with Control+D or with the command ``exit``. A first execution of ``$ nix shell`` may take some time, but for any future repetitions Nix will use cached packages and startup should be much faster.
You might be interested in creating multiple directories containing different ``flake.nix`` files which represent different sets of packages for different purposes. If you are familiar with Conda, using Nix in this way is similar to having multiple Conda environments. You might be interested in creating multiple directories containing different ``flake.nix`` files which represent different sets of packages for different purposes. If you are familiar with Conda, using Nix in this way is similar to having multiple Conda environments.
@ -159,7 +159,7 @@ Launch ``MSYS2 CLANG64`` from the Windows Start menu to open the MSYS2 shell, an
$ pacman -Syy $ pacman -Syy
$ pacman -S mingw-w64-clang-x86_64-artiq $ pacman -S mingw-w64-clang-x86_64-artiq
As above in the Nix section, you may find yourself wanting to add other useful packages (pandas, matplotlib, etc.). MSYS2 uses a port of ArchLinux's ``pacman`` to manage (add, remove, and update) packages. To add a specific package, you can simply use a command of the form: :: As above in the Nix section, you may find yourself wanting to add other useful packages (pandas, matplotlib, etc.). MSYS2 uses a port of ArchLinux's ``pacman`` to manage (add, remove, and update) packages. To add a specific package, you can simply use a command of the form: ::
$ pacman -S <package name> $ pacman -S <package name>
@ -202,10 +202,10 @@ This activation has to be performed in every new shell you open to make the ARTI
Upgrading ARTIQ Upgrading ARTIQ
--------------- ---------------
.. note:: .. note::
When you upgrade ARTIQ, as well as updating the software on your host machine, it may also be necessary to reflash the gateware and firmware of your core device to keep them compatible. New numbered release versions in particular incorporate breaking changes and are not generally compatible. See :doc:`flashing` for instructions. When you upgrade ARTIQ, as well as updating the software on your host machine, it may also be necessary to reflash the gateware and firmware of your core device to keep them compatible. New numbered release versions in particular incorporate breaking changes and are not generally compatible. See :doc:`flashing` for instructions.
Upgrading with Nix Upgrading with Nix
^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^
Run ``$ nix profile upgrade`` if you installed ARTIQ into your user profile. If you used a ``flake.nix`` shell environment, make a back-up copy of the ``flake.lock`` file to enable rollback, then run ``$ nix flake update`` and re-enter the environment with ``$ nix shell``. Run ``$ nix profile upgrade`` if you installed ARTIQ into your user profile. If you used a ``flake.nix`` shell environment, make a back-up copy of the ``flake.lock`` file to enable rollback, then run ``$ nix flake update`` and re-enter the environment with ``$ nix shell``.
@ -217,7 +217,7 @@ Upgrading with MSYS2
Run ``pacman -Syu`` to update all MSYS2 packages, including ARTIQ. If you get a message telling you that the shell session must be restarted after a partial update, open the shell again after the partial update and repeat the command. See the `MSYS2 <https://www.msys2.org/docs/updating/>`__ and `Pacman <https://wiki.archlinux.org/title/Pacman>`_ manuals for more information, including how to update individual packages if required. Run ``pacman -Syu`` to update all MSYS2 packages, including ARTIQ. If you get a message telling you that the shell session must be restarted after a partial update, open the shell again after the partial update and repeat the command. See the `MSYS2 <https://www.msys2.org/docs/updating/>`__ and `Pacman <https://wiki.archlinux.org/title/Pacman>`_ manuals for more information, including how to update individual packages if required.
Upgrading with Conda Upgrading with Conda
^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^
When upgrading ARTIQ or when testing different versions it is recommended that new Conda environments are created instead of upgrading the packages in existing environments. As a rule, keep previous environments around unless you are certain that they are no longer needed and the new environment is working correctly. When upgrading ARTIQ or when testing different versions it is recommended that new Conda environments are created instead of upgrading the packages in existing environments. As a rule, keep previous environments around unless you are certain that they are no longer needed and the new environment is working correctly.

39
doc/manual/list_of_ndsps.rst
View File

@ -3,30 +3,19 @@ List of available NDSPs
The following network device support packages are available for ARTIQ. If you would like to add yours to this list, just send us an email or a pull request. The following network device support packages are available for ARTIQ. If you would like to add yours to this list, just send us an email or a pull request.
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+ .. csv-table::
| Equipment | Nix package | MSYS2 package | Documentation | URL | :header: Equipment, Nix package, MSYS2 package, Documentation, URL
+=================================+===================================+==================================+===================================================================+========================================================+
| PDQ2 | Not available | Not available | `HTML <https://pdq.readthedocs.io>`_ | https://github.com/m-labs/pdq | PDQ2, Not available, Not available, `HTML <https://pdq.readthedocs.io>`_, `GitHub <https://github.com/m-labs/pdq>`__
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+ Lab Brick Digital Attenuator, ``lda``, ``lda``, Not available, `GitHub <https://github.com/m-labs/lda>`__
| Lab Brick Digital Attenuator | ``lda`` | ``lda`` | Not available | https://github.com/m-labs/lda | Novatech 4098B, ``novatech409b``, ``novatech409b``, Not available, `GitHub <https://github.com/m-labs/novatech409b>`__
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+ Thorlabs T-Cubes, ``thorlabs_tcube``, ``thorlabs_tcube``, Not available, `GitHub <https://github.com/m-labs/thorlabs_tcube>`__
| Novatech 409B | ``novatech409b`` | ``novatech409b`` | Not available | https://github.com/m-labs/novatech409b | Korad KA3005P, ``korad_ka3005p``, ``korad_ka3005p``, Not available, `GitHub <https://github.com/m-labs/korad_ka3005p>`__
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+ Newfocus 8742, ``newfocus8742``, ``newfocus8742``, Not available, `GitHub <https://github.com/quartiq/newfocus8742>`__
| Thorlabs T-Cubes | ``thorlabs_tcube`` | ``thorlabs_tcube`` | Not available | https://github.com/m-labs/thorlabs_tcube | Princeton Instruments PICam, Not available, Not available, Not available, `GitHub <https://github.com/quartiq/picam>`__
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+ Anel HUT2 power distribution, ``hut2``, Not available, Not available, `GitHub <https://github.com/quartiq/hut2>`__
| Korad KA3005P | ``korad_ka3005p`` | ``korad_ka3005p`` | Not available | https://github.com/m-labs/korad_ka3005p | TOPTICA lasers, ``toptica-lasersdk-artiq``, Not available, Not available, `GitHub <https://github.com/quartiq/lasersdk-artiq>`__
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+ HighFinesse wavemeters, ``highfinesse-net``, Not available, Not available, `GitHub <https://github.com/quartiq/highfinesse-net>`__
| Newfocus 8742 | ``newfocus8742`` | ``newfocus8742`` | Not available | https://github.com/quartiq/newfocus8742 | InfluxDB database, Not available, Not available, `HTML <https://gitlab.com/charlesbaynham/artiq_influx_generic>`__, `GitHub <https://gitlab.com/charlesbaynham/artiq_influx_generic>`__
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+
| Princeton Instruments PICam | Not available | Not available | Not available | https://github.com/quartiq/picam |
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+
| Anel HUT2 power distribution | ``hut2`` | Not available | Not available | https://github.com/quartiq/hut2 |
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+
| TOPTICA lasers | ``toptica-lasersdk-artiq`` | Not available | Not available | https://github.com/quartiq/lasersdk-artiq |
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+
| HighFinesse wavemeters | ``highfinesse-net`` | Not available | Not available | https://github.com/quartiq/highfinesse-net |
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+
| InfluxDB database | Not available | Not available | `HTML <https://gitlab.com/charlesbaynham/artiq_influx_generic>`__ | https://gitlab.com/charlesbaynham/artiq_influx_generic |
+---------------------------------+-----------------------------------+----------------------------------+-------------------------------------------------------------------+--------------------------------------------------------+
MSYS2 packages all start with the ``mingw-w64-clang-x86_64-`` prefix. MSYS2 packages all start with the ``mingw-w64-clang-x86_64-`` prefix.

71
doc/manual/rtio.rst
View File

@ -5,28 +5,17 @@ ARTIQ Real-Time I/O Concepts
The ARTIQ Real-Time I/O design employs several concepts to achieve its goals of high timing resolution on the nanosecond scale and low latency on the microsecond scale while still not sacrificing a readable and extensible language. The ARTIQ Real-Time I/O design employs several concepts to achieve its goals of high timing resolution on the nanosecond scale and low latency on the microsecond scale while still not sacrificing a readable and extensible language.
In a typical environment two very different classes of hardware need to be controlled. In a typical environment two very different classes of hardware need to be controlled. One class is the vast arsenal of diverse laboratory hardware that interfaces with and is controlled from a typical PC. The other is specialized real-time hardware that requires tight coupling and a low-latency interface to a CPU. The ARTIQ code that describes a given experiment is composed of two types of "programs": regular Python code that is executed on the host and ARTIQ *kernels* that are executed on a *core device*. The CPU that executes the ARTIQ kernels has direct access to specialized programmable I/O timing logic (part of the *gateware*). The two types of code can invoke each other and transitions between them are seamless.
One class is the vast arsenal of diverse laboratory hardware that interfaces with and is controlled from a typical PC.
The other is specialized real-time hardware that requires tight coupling and a low-latency interface to a CPU.
The ARTIQ code that describes a given experiment is composed of two types of "programs":
regular Python code that is executed on the host and ARTIQ *kernels* that are executed on a *core device*.
The CPU that executes the ARTIQ kernels has direct access to specialized programmable I/O timing logic (part of the *gateware*).
The two types of code can invoke each other and transitions between them are seamless.
The ARTIQ kernels do not interface with the real-time gateware directly. The ARTIQ kernels do not interface with the real-time gateware directly. That would lead to imprecise, indeterminate, and generally unpredictable timing. Instead the CPU operates at one end of a bank of FIFO (first-in-first-out) buffers while the real-time gateware at the other end guarantees the *all or nothing* level of excellent timing precision.
That would lead to imprecise, indeterminate, and generally unpredictable timing.
Instead the CPU operates at one end of a bank of FIFO (first-in-first-out) buffers while the real-time gateware at the other end guarantees the *all or nothing* level of excellent timing precision.
A FIFO for an output channel holds timestamps and event data describing when and what is to be executed. A FIFO for an output channel holds timestamps and event data describing when and what is to be executed. The CPU feeds events into this FIFO. A FIFO for an input channel contains timestamps and event data for events that have been recorded by the real-time gateware and are waiting to be read out by the CPU on the other end.
The CPU feeds events into this FIFO.
A FIFO for an input channel contains timestamps and event data for events that have been recorded by the real-time gateware and are waiting to be read out by the CPU on the other end.
Timeline and terminology Timeline and terminology
------------------------ ------------------------
The set of all input and output events on all channels constitutes the *timeline*. The set of all input and output events on all channels constitutes the *timeline*. A high-resolution wall clock (``rtio_counter_mu``) counts clock cycles and manages the precise timing of the events. Output events are executed when their timestamp matches the current clock value. Input events are recorded when they reach the gateware and stamped with the current clock value accordingly.
A high-resolution wall clock (``rtio_counter_mu``) counts clock cycles and manages the precise timing of the events. Output events are executed when their timestamp matches the current clock value. Input events are recorded when they reach the gateware and stamped with the current clock value accordingly.
The kernel runtime environment maintains a timeline cursor (called ``now_mu``) used as the timestamp when output events are submitted to the FIFOs. Both ``now_mu`` and ``rtio_counter_mu`` are counted in integer *machine units,* or mu, rather than SI units. The machine unit represents the maximum resolution of RTIO timing in an ARTIQ system. The duration of a machine unit is the *reference period* of the system, and may be changed by the user, but normally corresponds to a duration of one nanosecond. The kernel runtime environment maintains a timeline cursor (called ``now_mu``) used as the timestamp when output events are submitted to the FIFOs. Both ``now_mu`` and ``rtio_counter_mu`` are counted in integer *machine units,* or mu, rather than SI units. The machine unit represents the maximum resolution of RTIO timing in an ARTIQ system. The duration of a machine unit is the *reference period* of the system, and may be changed by the user, but normally corresponds to a duration of one nanosecond.
@ -34,34 +23,22 @@ The timeline cursor ``now_mu`` can be moved forward or backward on the timeline
RTIO timestamps, the timeline cursor, and the ``rtio_counter_mu`` wall clock are all counted relative to the core device startup/boot time. The wall clock keeps running across experiments. RTIO timestamps, the timeline cursor, and the ``rtio_counter_mu`` wall clock are all counted relative to the core device startup/boot time. The wall clock keeps running across experiments.
Absolute timestamps can be large numbers. Absolute timestamps can be large numbers. They are represented internally as 64-bit integers. With a typical one-nanosecond machine unit, this covers a range of hundreds of years. Conversions between such a large integer number and a floating point representation can cause loss of precision through cancellation. When computing the difference of absolute timestamps, use ``self.core.mu_to_seconds(t2-t1)``, not ``self.core.mu_to_seconds(t2)-self.core.mu_to_seconds(t1)`` (see :meth:`~artiq.coredevice.core.Core.mu_to_seconds`). When accumulating time, do it in machine units and not in SI units, so that rounding errors do not accumulate.
They are represented internally as 64-bit integers.
With a typical one-nanosecond machine unit, this covers a range of hundreds of years.
Conversions between such a large integer number and a floating point representation can cause loss of precision through cancellation.
When computing the difference of absolute timestamps, use ``self.core.mu_to_seconds(t2-t1)``, not ``self.core.mu_to_seconds(t2)-self.core.mu_to_seconds(t1)`` (see :meth:`~artiq.coredevice.core.Core.mu_to_seconds`).
When accumulating time, do it in machine units and not in SI units, so that rounding errors do not accumulate.
.. note:: .. note::
Absolute timestamps are also referred to as *RTIO fine timestamps,* because they run on a significantly finer resolution than the timestamps provided by the so-called *coarse RTIO clock,* the actual clocking signal provided to or generated by the core device. Absolute timestamps are also referred to as *RTIO fine timestamps,* because they run on a significantly finer resolution than the timestamps provided by the so-called *coarse RTIO clock,* the actual clocking signal provided to or generated by the core device. The frequency of the coarse RTIO clock is set by the core device :ref:`clocking settings <core-device-clocking>` but is most commonly 125MHz, which corresponds to eight one-nanosecond machine units per coarse RTIO cycle.
The frequency of the coarse RTIO clock is set by the core device :ref:`clocking settings <core-device-clocking>` but is most commonly 125MHz, which corresponds to eight one-nanosecond machine units per coarse RTIO cycle.
The *coarse timestamp* of an event is its timestamp as according to the lower resolution of the coarse clock. The *coarse timestamp* of an event is its timestamp as according to the lower resolution of the coarse clock. It is in practice a truncated version of the fine timestamp. In general, ARTIQ offers *precision* on the fine level, but *operates* at the coarse level; this is rarely relevant to the user, but understanding it may clarify the behavior of some RTIO issues (e.g. sequence errors).
It is in practice a truncated version of the fine timestamp.
In general, ARTIQ offers *precision* on the fine level, but *operates* at the coarse level; this is rarely relevant to the user, but understanding it may clarify the behavior of some RTIO issues (e.g. sequence errors).
.. Related: https://github.com/m-labs/artiq/issues/1237 .. Related: https://github.com/m-labs/artiq/issues/1237
The following basic example shows how to place output events on the timeline. The following basic example shows how to place output events on the timeline. It emits a precisely timed 2 µs pulse::
It emits a precisely timed 2 µs pulse::
ttl.on() ttl.on()
delay(2*us) delay(2*us)
ttl.off() ttl.off()
The device ``ttl`` represents a single digital output channel (:class:`artiq.coredevice.ttl.TTLOut`). The device ``ttl`` represents a single digital output channel (:class:`artiq.coredevice.ttl.TTLOut`). The :meth:`artiq.coredevice.ttl.TTLOut.on` method places an rising edge on the timeline at the current cursor position (``now_mu``). Then the cursor is moved forward 2 µs and a falling edge is placed at the new cursor position. Later, when the wall clock reaches the respective timestamps, the RTIO gateware executes the two events.
The :meth:`artiq.coredevice.ttl.TTLOut.on` method places an rising edge on the timeline at the current cursor position (``now_mu``).
Then the cursor is moved forward 2 µs and a falling edge is placed at the new cursor position.
Later, when the wall clock reaches the respective timestamps, the RTIO gateware executes the two events.
The following diagram shows what is going on at the different levels of the software and gateware stack (assuming one machine unit of time is 1 ns): The following diagram shows what is going on at the different levels of the software and gateware stack (assuming one machine unit of time is 1 ns):
@ -88,7 +65,7 @@ This sequence is exactly equivalent to::
ttl.pulse(2*us) ttl.pulse(2*us)
This method :meth:`artiq.coredevice.ttl.TTLOut.pulse` advances the timeline cursor (using :func:`~artiq.language.core.delay` internally) by exactly the amount given. Other methods such as :meth:`~artiq.coredevice.ttl.TTLOut.on`, :meth:`~artiq.coredevice.ttl.TTLOut.off`, :meth:`~artiq.coredevice.ad9914.AD9914.set` do not modify the timeline cursor. The latter are called *zero-duration* methods. This method :meth:`artiq.coredevice.ttl.TTLOut.pulse` advances the timeline cursor (using :func:`~artiq.language.core.delay` internally) by exactly the amount given. ther methods such as :meth:`~artiq.coredevice.ttl.TTLOut.on`, :meth:`~artiq.coredevice.ttl.TTLOut.off`, :meth:`~artiq.coredevice.ad9914.AD9914.set` do not modify the timeline cursor. The latter are called *zero-duration* methods.
Output errors and exceptions Output errors and exceptions
---------------------------- ----------------------------
@ -96,11 +73,7 @@ Output errors and exceptions
Underflows Underflows
^^^^^^^^^^ ^^^^^^^^^^
A RTIO ouput event must always be programmed with a timestamp in the future. A RTIO ouput event must always be programmed with a timestamp in the future. In other words, the timeline cursor ``now_mu`` must be in advance of the current wall clock ``rtio_counter_mu``: the past cannot be altered. The following example tries to place a rising edge event on the timeline. If the current cursor is in the past, an :class:`artiq.coredevice.exceptions.RTIOUnderflow` exception is thrown. The experiment attempts to handle the exception by moving the cursor forward and repeating the programming of the rising edge::
In other words, the timeline cursor ``now_mu`` must be in advance of the current wall clock ``rtio_counter_mu``: the past cannot be altered.
The following example tries to place a rising edge event on the timeline.
If the current cursor is in the past, an :class:`artiq.coredevice.exceptions.RTIOUnderflow` exception is thrown.
The experiment attempts to handle the exception by moving the cursor forward and repeating the programming of the rising edge::
try: try:
ttl.on() ttl.on()
@ -109,8 +82,7 @@ The experiment attempts to handle the exception by moving the cursor forward and
delay(16.6667*ms) delay(16.6667*ms)
ttl.on() ttl.on()
Once the timeline cursor has overtaken the wall clock, the exception does not reoccur and the event can be scheduled successfully. Once the timeline cursor has overtaken the wall clock, the exception does not reoccur and the event can be scheduled successfully. This can also be thought of as adding positive slack to the system.
This can also be thought of as adding positive slack to the system.
.. wavedrom:: .. wavedrom::
@ -180,17 +152,13 @@ Offending event(s) are discarded and the problem is reported asynchronously via
Input channels and events Input channels and events
------------------------- -------------------------
Input channels detect events, timestamp them, and place them in a buffer for the experiment to read out. Input channels detect events, timestamp them, and place them in a buffer for the experiment to read out. The following example counts the rising edges occurring during a precisely timed 500 ns interval. If more than 20 rising edges are received, it outputs a pulse::
The following example counts the rising edges occurring during a precisely timed 500 ns interval.
If more than 20 rising edges are received, it outputs a pulse::
if input.count(input.gate_rising(500*ns)) > 20: if input.count(input.gate_rising(500*ns)) > 20:
delay(2*us) delay(2*us)
output.pulse(500*ns) output.pulse(500*ns)
Note that many input methods will necessarily involve the wall clock catching up to the timeline cursor or advancing before it. Note that many input methods will necessarily involve the wall clock catching up to the timeline cursor or advancing before it. This is to be expected: managing output events means working to plan the future, but managing input events means working to react to the past. For input channels, it is the past that is under discussion.
This is to be expected: managing output events means working to plan the future, but managing input events means working to react to the past.
For input channels, it is the past that is under discussion.
In this case, the :meth:`~artiq.coredevice.ttl.TTLInOut.gate_rising` waits for the duration of the 500ns interval (or *gate window*) and records an event for each rising edge. At the end of the interval it exits, leaving the timeline cursor at the end of the interval (``now_mu = rtio_counter_mu``). :meth:`~artiq.coredevice.ttl.TTLInOut.count` unloads these events from the input buffers and counts the number of events recorded, during which the wall clock necessarily advances (``rtio_counter_mu > now_mu``). Accordingly, before we place any further output events, a :func:`~artiq.language.core.delay` is necessary to re-establish positive slack. In this case, the :meth:`~artiq.coredevice.ttl.TTLInOut.gate_rising` waits for the duration of the 500ns interval (or *gate window*) and records an event for each rising edge. At the end of the interval it exits, leaving the timeline cursor at the end of the interval (``now_mu = rtio_counter_mu``). :meth:`~artiq.coredevice.ttl.TTLInOut.count` unloads these events from the input buffers and counts the number of events recorded, during which the wall clock necessarily advances (``rtio_counter_mu > now_mu``). Accordingly, before we place any further output events, a :func:`~artiq.language.core.delay` is necessary to re-establish positive slack.
@ -220,13 +188,7 @@ Similar situations arise with methods such as :meth:`TTLInOut.sample_get <artiq.
Overflow exceptions Overflow exceptions
^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^
The RTIO input channels buffer input events received while an input gate is open, or when using the sampling API (:meth:`TTLInOut.sample_input <artiq.coredevice.ttl.TTLInOut.sample_input>`) at certain points in time. The RTIO input channels buffer input events received while an input gate is open, or when using the sampling API (:meth:`TTLInOut.sample_input <artiq.coredevice.ttl.TTLInOut.sample_input>`) at certain points in time. The events are kept in a FIFO until the CPU reads them out via e.g. :meth:`~artiq.coredevice.ttl.TTLInOut.count`, :meth:`~artiq.coredevice.ttl.TTLInOut.timestamp_mu` or :meth:`~artiq.coredevice.ttl.TTLInOut.sample_get`. The size of these FIFOs is finite and specified in gateware; in practice, it is limited by the resources available to the FPGA, and therefore differs depending on the specific core device being used. If a FIFO is full and another event comes in, this causes an overflow condition. The condition is converted into an :class:`~artiq.coredevice.exceptions.RTIOOverflow` exception that is raised on a subsequent invocation of one of the readout methods. Overflow exceptions are generally best dealt with simply by reading out from the input buffers more frequently. In odd or particular cases, users may consider modifying the length of individual buffers in gateware.
The events are kept in a FIFO until the CPU reads them out via e.g. :meth:`~artiq.coredevice.ttl.TTLInOut.count`, :meth:`~artiq.coredevice.ttl.TTLInOut.timestamp_mu` or :meth:`~artiq.coredevice.ttl.TTLInOut.sample_get`.
The size of these FIFOs is finite and specified in gateware; in practice, it is limited by the resources available to the FPGA, and therefore differs depending on the specific core device being used.
If a FIFO is full and another event comes in, this causes an overflow condition.
The condition is converted into an :class:`~artiq.coredevice.exceptions.RTIOOverflow` exception that is raised on a subsequent invocation of one of the readout methods.
Overflow exceptions are generally best dealt with simply by reading out from the input buffers more frequently. In odd or particular cases, users may consider modifying the length of individual buffers in gateware.
.. note:: .. note::
It is not possible to provoke an :class:`~artiq.coredevice.exceptions.RTIOOverflow` on a RTIO output channel. While output buffers are also of finite size, and can be filled up, the CPU will simply stall the submission of further events until it is once again possible to buffer them. Among other things, this means that padding the timeline cursor with large amounts of positive slack is not always a valid strategy to avoid :class:`~artiq.coredevice.exceptions.RTIOOverflow` exceptions when generating fast event sequences. In practice only a fixed number of events can be generated in advance, and the rest of the processing will be carried out when the wall clock is much closer to ``now_mu``. It is not possible to provoke an :class:`~artiq.coredevice.exceptions.RTIOOverflow` on a RTIO output channel. While output buffers are also of finite size, and can be filled up, the CPU will simply stall the submission of further events until it is once again possible to buffer them. Among other things, this means that padding the timeline cursor with large amounts of positive slack is not always a valid strategy to avoid :class:`~artiq.coredevice.exceptions.RTIOOverflow` exceptions when generating fast event sequences. In practice only a fixed number of events can be generated in advance, and the rest of the processing will be carried out when the wall clock is much closer to ``now_mu``.
@ -251,8 +213,7 @@ Note that event spreading can be particularly helpful in DRTIO satellites, as it
Seamless handover Seamless handover
----------------- -----------------
The timeline cursor persists across kernel invocations. The timeline cursor persists across kernel invocations. This is demonstrated in the following example where a pulse is split across two kernels::
This is demonstrated in the following example where a pulse is split across two kernels::
def run(): def run():
k1() k1()