The core device is a FPGA-based hardware component that contains a softcore or hardcore CPU tightly coupled with the so-called RTIO core, which runs in gateware and provides precision timing. The CPU executes Python code that is statically compiled by the ARTIQ compiler and communicates with peripherals (TTL, DDS, etc.) through the RTIO core, as described in :ref:`artiq-real-time-i-o-concepts`. 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.
The core device contains some flash storage space which is largely used to store configuration data. It is one sector (typically 64 kB) large and organized as a list of key-value records, accessible by using ``artiq_coremgmt`` (see: :ref:`core-device-management-tool`).
This area is used to store a variety of configurations, in particular the core device IP address and, if present, the startup and/or idle kernels (see also: :ref:`miscellaneous-configuration-of-the-core-device`).
`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/sinara-hw/meta/wiki>`_ family of boards. All variants support interfacing to various EEM daughterboards (TTL, DDS, ADC, DAC...) connected directly to it.
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 RTIO clock frequency is 125MHz or 150MHz, which is generated by the Si5324.
DRTIO master variants
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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
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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.
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.
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.
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:
KC705 in DRTIO variants and Kasli generate the RTIO clock using a PLL locked either to an internal crystal or to an external frequency reference. Valid values are:
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.
