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.
The main target board for the ARTIQ core device is the KC705 development board from Xilinx. It supports the NIST QC1 hardware via an adapter, and the NIST CLOCK and QC2 hardware (FMC).
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.
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 low-cost Pipistrello FPGA board can be used as a lower-cost but slower alternative. Since the device does not have a native network interface, a PPP session is run over the serial port (which is then run over USB). To establish the PPP session with the core device, giving it the IP address 10.0.0.2, as root execute::
pppd /dev/ttyUSB1 115200 noauth nodetach local nocrtscts novj 10.0.0.1:10.0.0.2
..warning:: The Pipistrello draws a high current over USB, and that current increases when the FPGA design is active. If you experience problems such as intermittent board freezes or USB errors, try connecting it to a self-powered USB hub.
The input only limitation on channels 0 and 1 comes from the QC-DAQ adapter. When the adapter is not used (and physically unplugged from the Pipistrello board), the corresponding pins on the Pipistrello can be used as outputs. Do not configure these channels as outputs when the adapter is plugged, as this would cause electrical contention.
The board can accept an external RTIO clock connected to PMT2. If the DDS box does not drive the PMT2 pair, use XTRIG and patch the XTRIG transceiver output on the adapter board onto C:15 disconnecting PMT2.
