RiscyD2 is a tiny RISC-V based microcontroller/softcore running on a Digilent Arty A7-35T board.
- chip: RTL code for a RISC-V CPU core implementing the RV32I base instruction set, with M standard extension support.
- binutils: Contains an assembler that emits RISC-V flat binary.
- emulation: A RISC-V RV32IM emulator written in Python.
- test: Simple unit tests for arithemtic, load/store and csr instructions.
The project is mainly educational, and is inspired by From the Transistor to the Web Browser.
- Icarus Verilog
- Python3
- PySerial
RiscyD2 currently only supports Arty A7-35T, but the plan is to add support for more boards.
To set it up:
- Compile the
bootrom:
python3 binutils/asm/asm.py -i os/bootrom.asm -o code.o
- Save the
code.memfile you got from the previous step - Create a Vivado project
- Add the content of
chip/rtlas design sources - Add
code.memas a Memory file - Add constraints located under
chip/fpga/arty_a7/arty_a7_35t.xdcas constraint file - Synthesize, implement and generate bitstream
- Load the bitstream to the board
At this point the chip is deployed to the board, and the bootrom is running. It continously checks the UART port for incoming exe files.
To compile programs for the board you can either use the assembler in the repository (recommended to run the programs in the sample folder), or use a real compiler, like GCC.
Compile an example program located under sample:
python3 binutils/asm/asm.py -i sample/switches.asm -o exe.o
For a relatively complex example program, see the porting of TinyMaix to RiscyD2.
To compile C programs, the following toolchain is recommended:
- GCC
- Picolibc
- riscyd2.h
- riscyd2.ld (Picolibc linker script)
Send the exe through UART:
python3 tools/talk2d2.py -i path/to/exe
The binary format is fairly simple: the first 4 bytes encode the size of the exe, followed by the exe. That's it.
To listen to incoming data from the board, run:
python3 tools/listen2d2.py
(NOTE: to get the ID of your board run ls /dev/tty.* in your terminal.)
MIT