Add Support for Digilent Arty-A7 100T FPGA Board

[WorldofJARcraft]

This patch adds support for the Arty A7 FPGA (#154).

Overview

• Adds support for Arty A7 100T FPGA variant, running CVA6 at 25 MHz
• Connects debug module via built-in USB-JTAG
• Connects USB UART
• SPI/SD via JA PMOD
• Adds cv64a6_imac configuration
• Tested with Xilinx Vivado v2023.2

Changed

• Added constraints and configurations for Arty A7
• Backported BSCANE2 probe for debug interface from riscv-dbg. I have placed the updated files in a separate directory, they are only ever compiled when building for the A7. Simulation, ASIC flows and other FPGA boards continue to use the current version of riscv-dbg.
• Backported common-cells needed for BSCANE2 debug. Not used when building anything except ARTY A7.

What I have been able to test so far:

• Design meets timing for cv32a6_imac_sv32 @ 25 MHz
• bootrom runs and detects that no SD card exists
• debugging via openocd/gdb works via the built-in USB JTAG
• zephyr hello-world example can be loaded and debugged via west debug and west flash in both 32 and 64 bit configs and runs as expected (zephyr PR coming soon)
• Resetting the CPU with the "Reset" button
• USB UART output works
• A reduced 64-bit config (cv64imac) fits the board, meets timing and runs a hello world example with zephyr. I have added it to the PR.
• A cv64imafdc_fpga configuration, in which I have enabled CVA6ConfigFpgaEn, i.e., inferring memories as block RAM, meets timing and fits the board with appx. 5000 LUTs to spare.
• Booting 64-bit Linux from an MicroSD PMOD. I will send a PR for the software stack soon.

What I have not yet tested:

• Other Arty variants (e.g., S7, A7-35T). I do not have access to these boards.

What does not work:

• Full cv64a6_imafdc_sv39 config (i.e., without CVA6ConfigFpgaEn) does not fit the board, uses appx. 1000 LUTs too much. Might fit when sacrificing a peripheral (e.g., debug, SPI, GPIO, ...)
• Ethernet support due to timing/resource constraints (but could possibly fit with 32 bit SoCs)

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[WorldofJARcraft]

For reference, here is the forked software stack: https://github.com/WorldofJARcraft/cva6-sdk
I will create pull requests as soon as the hardware PR has been accepted.

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👋 Hi there!

This pull request seems inactive. Need more help or have updates? Feel free to let us know. If there are no updates within the next few days, we'll go ahead and close this PR. 😊

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