Core device
===========

The core device is a FPGA-based hardware component that contains a softcore CPU tightly coupled with the so-called RTIO core that provides precision timing. The CPU executes Python code that is statically compiled by the ARTIQ compiler, and communicates with the core device peripherals (TTL, DDS, etc.) over the RTIO core. This architecture provides high timing resolution, low latency, low jitter, high level programming capabilities, and good integration with the rest of the Python experiment code.

While it is possible to use all the other parts of ARTIQ (controllers, master, GUI, dataset management, etc.) without a core device, many experiments require it.


.. _core-device-flash-storage:

Flash storage
*************

The core device contains some flash space that can be used to store configuration data.

This storage area is used to store the core device MAC address, IP address and even the idle kernel.

The flash storage area is one sector (typically 64 kB) large and is organized as a list of key-value records.

This flash storage space can be accessed by using ``artiq_coremgmt`` (see: :ref:`core-device-management-tool`).

.. _board-ports:

FPGA board ports
****************

All boards have a serial interface running at 115200bps 8-N-1 that can be used for debugging.

Kasli
-----

`Kasli <https://github.com/m-labs/sinara/wiki/Kasli>`_ is a versatile core device designed for ARTIQ as part of the `Sinara <https://github.com/m-labs/sinara/wiki>`_ family of boards. All variants support interfacing to various EEM daughterboards (TTL, DDS, ADC, DAC...) connected directly to it.

Standalone variants
+++++++++++++++++++

Kasli is connected to the network using a 1000Base-X SFP module. `No-name <https://www.fs.com>`_ BiDi (1000Base-BX) modules have been used successfully. The SFP module for the network should be installed into the SFP0 cage.
The other SFP cages are not used.

The RTIO clock frequency is 125MHz or 150MHz, which is generated by the Si5324.

DRTIO master variants
+++++++++++++++++++++

Kasli can be used as a DRTIO master that provides local RTIO channels and can additionally control one DRTIO satellite.

The RTIO clock frequency is 125MHz or 150MHz, which is generated by the Si5324. The DRTIO line rate is 2.5Gbps or 3Gbps.

As with the standalone configuration, the SFP module for the Ethernet network should be installed into the SFP0 cage. The DRTIO connections are on SFP1 and SFP2, and optionally on the SATA connector.

DRTIO satellite/repeater variants
+++++++++++++++++++++++++++++++++

Kasli can be used as a DRTIO satellite with a 125MHz or 150MHz RTIO clock and a 2.5Gbps or 3Gbps DRTIO line rate.

The DRTIO upstream connection is on SFP0 or optionally on the SATA connector, and the remaining SFPs are downstream ports.

KC705
-----

An alternative target board for the ARTIQ core device is the KC705 development board from Xilinx. It supports the NIST CLOCK and QC2 hardware (FMC).

Common problems
+++++++++++++++

* The SW13 switches on the board need to be set to 00001.
* When connected, the CLOCK adapter breaks the JTAG chain due to TDI not being connected to TDO on the FMC mezzanine.
* On some boards, the JTAG USB connector is not correctly soldered.

VADJ
++++

With the NIST CLOCK and QC2 adapters, for safe operation of the DDS buses (to prevent damage to the IO banks of the FPGA), the FMC VADJ rail of the KC705 should be changed to 3.3V. Plug the Texas Instruments USB-TO-GPIO PMBus adapter into the PMBus connector in the corner of the KC705 and use the Fusion Digital Power Designer software to configure (requires Windows). Write to chip number U55 (address 52), channel 4, which is the VADJ rail, to make it 3.3V instead of 2.5V.  Power cycle the KC705 board to check that the startup voltage on the VADJ rail is now 3.3V.


NIST CLOCK
++++++++++

With the CLOCK hardware, the TTL lines are mapped as follows:

+--------------------+-----------------------+--------------+
| RTIO channel       | TTL line              | Capability   |
+====================+=======================+==============+
| 3,7,11,15          | TTL3,7,11,15          | Input+Output |
+--------------------+-----------------------+--------------+
| 0-2,4-6,8-10,12-14 | TTL0-2,4-6,8-10,12-14 | Output       |
+--------------------+-----------------------+--------------+
| 16                 | PMT0                  | Input        |
+--------------------+-----------------------+--------------+
| 17                 | PMT1                  | Input        |
+--------------------+-----------------------+--------------+
| 18                 | SMA_GPIO_N            | Input+Output |
+--------------------+-----------------------+--------------+
| 19                 | LED                   | Output       |
+--------------------+-----------------------+--------------+
| 20                 | AMS101_LDAC_B         | Output       |
+--------------------+-----------------------+--------------+
| 21                 | LA32_P                | Clock        |
+--------------------+-----------------------+--------------+

The board has RTIO SPI buses mapped as follows:

+--------------+------------------+--------------+--------------+------------+
| RTIO channel | CS_N             | MOSI         | MISO         | CLK        |
+==============+==================+==============+==============+============+
| 22           | AMS101_CS_N      | AMS101_MOSI  |              | AMS101_CLK |
+--------------+------------------+--------------+--------------+------------+
| 23           | SPI0_CS_N        | SPI0_MOSI    | SPI0_MISO    | SPI0_CLK   |
+--------------+------------------+--------------+--------------+------------+
| 24           | SPI1_CS_N        | SPI1_MOSI    | SPI1_MISO    | SPI1_CLK   |
+--------------+------------------+--------------+--------------+------------+
| 25           | SPI2_CS_N        | SPI2_MOSI    | SPI2_MISO    | SPI2_CLK   |
+--------------+------------------+--------------+--------------+------------+
| 26           | MMC_SPI_CS_N     | MMC_SPI_MOSI | MMC_SPI_MISO | MMC_SPI_CLK|
+--------------+------------------+--------------+--------------+------------+

The DDS bus is on channel 27.


NIST QC2
++++++++

With the QC2 hardware, the TTL lines are mapped as follows:

+--------------------+-----------------------+--------------+
| RTIO channel       | TTL line              | Capability   |
+====================+=======================+==============+
| 0-39               | TTL0-39               | Input+Output |
+--------------------+-----------------------+--------------+
| 40                 | SMA_GPIO_N            | Input+Output |
+--------------------+-----------------------+--------------+
| 41                 | LED                   | Output       |
+--------------------+-----------------------+--------------+
| 42                 | AMS101_LDAC_B         | Output       |
+--------------------+-----------------------+--------------+
| 43, 44             | CLK0, CLK1            | Clock        |
+--------------------+-----------------------+--------------+

The board has RTIO SPI buses mapped as follows:

+--------------+-------------+-------------+-----------+------------+
| RTIO channel | CS_N        | MOSI        | MISO      | CLK        |
+==============+=============+=============+===========+============+
| 45           | AMS101_CS_N | AMS101_MOSI |           | AMS101_CLK |
+--------------+-------------+-------------+-----------+------------+
| 46           | SPI0_CS_N   | SPI0_MOSI   | SPI0_MISO | SPI0_CLK   |
+--------------+-------------+-------------+-----------+------------+
| 47           | SPI1_CS_N   | SPI1_MOSI   | SPI1_MISO | SPI1_CLK   |
+--------------+-------------+-------------+-----------+------------+
| 48           | SPI2_CS_N   | SPI2_MOSI   | SPI2_MISO | SPI2_CLK   |
+--------------+-------------+-------------+-----------+------------+
| 49           | SPI3_CS_N   | SPI3_MOSI   | SPI3_MISO | SPI3_CLK   |
+--------------+-------------+-------------+-----------+------------+

There are two DDS buses on channels 50 (LPC, DDS0-DDS11) and 51 (HPC, DDS12-DDS23).


The QC2 hardware uses TCA6424A I2C I/O expanders to define the directions of its TTL buffers. There is one such expander per FMC card, and they are selected using the PCA9548 on the KC705.

To avoid I/O contention, the startup kernel should first program the TCA6424A expanders and then call ``output()`` on all ``TTLInOut`` channels that should be configured as outputs.

See :mod:`artiq.coredevice.i2c` for more details.

Clocking
++++++++

The KC705 in standalone variants supports an internal 125 MHz RTIO clock (based on its crystal oscillator, or external reference for PLL for DRTIO variants) and an external clock, that can be selected using the ``rtio_clock`` configuration entry. Valid values are:

    * ``int_125`` - internal crystal oscillator, 125 MHz output (default),
    * ``ext0_bypass`` - external clock.

KC705 in DRTIO variants and Kasli generates the RTIO clock using a PLL locked either to an internal crystal or to an external frequency reference. Valid values are:

    * ``int_125`` - internal crystal oscillator using PLL, 125 MHz output (default),
    * ``int_100`` - internal crystal oscillator using PLL, 100 MHz output,
    * ``int_150`` - internal crystal oscillator using PLL, 150 MHz output,
    * ``ext0_synth0_10to125`` - external 10 MHz reference using PLL, 125 MHz output,
    * ``ext0_synth0_80to125`` - external 80 MHz reference using PLL, 125 MHz output,
    * ``ext0_synth0_100to125`` - external 100 MHz reference using PLL, 125 MHz output,
    * ``ext0_synth0_125to125`` - external 125 MHz reference using PLL, 125 MHz output,
    * ``ext0_bypass``, ``ext0_bypass_125``, ``ext0_bypass_100`` - external clock - with explicit aliases available.

The selected option can be observed in the core device boot logs.

Options ``rtio_clock=int_XXX`` and ``rtio_clock=ext0_synth0_XXXXX`` generate the RTIO clock using a PLL locked either to an internal crystal or to an external frequency reference (depending on exact option). ``rtio_clock=ext0_bypass`` bypasses that PLL and the user must supply the RTIO clock (typically 125 MHz) at the Kasli front panel SMA input. Bypassing the PLL ensures the skews between input clock, Kasli downstream clock outputs, and RTIO clock are deterministic accross reboots of the system. This is useful when phase determinism is required in situtations where the reference clock fans out to other devices before reaching Kasli.
