twitchcore
A RISC-V core, first in Python, then in Verilog, then on FPGA.
Getting Started
Prerequisites
- icarus-verilog
- riscv-gnu-toolchain
brew install icarus-verilog riscv-gnu-toolchainInstallation
- Clone this repo
git clone https://github.com/geohot/twitchcore
cd twitchcore- Clone and build
riscv-tests
git clone https://github.com/riscv/riscv-tests
cd riscv-tests
git submodule update --init --recursive
autoconf
./configure
make
make install
cd ..- Create a virtual environment (optional)
python3 -m venv env
source env/bin/activate- Install Python packages
pip install -r requirements.txtTODO
- Fix unaligned loads/stores (I think this is good now, at least acceptable)
- Make pipelining work
- Add M instructions for fast multiply and divide
- Add better introspection
- Switch to 64-bit
- Add "RISK" ML accelerator ("K" Standard Extension)
TODO (later)
- Many ROBs like M1 go very fast
Notes on Memory system
8 million elements (20MB) = 23-bit address path
We want to support a load/store instruction into 32x32 matrix register (2432 bytes) like this:
- Would be R-Type with rs1 and rs2 (64-bit)
- rs1 contains the 23-bit base address, plus two masks in the upper bytes (0 is no mask)
- rs2 contains two 24-bit strides for x and y. Several of these bits aren't connected
- "rd" is the extension register to load into / store from
Use some hash function on the addresses to avoid "bank conflicts", can upper bound the fetch time.
Notes on ALU
matmul/mulacc are the big ones, 65536 FLOPS and 2048 FLOPS respectively
Have to think this through more with the reduce instructions too.
It's okay if the matmul takes multiple cycles I think, but the mulacc would be nice to be one.
matmul
- load with stride 0 in X
- mul
- reduce
Notes on mini edition in 100T
16x16 registers (608 bytes), 256 FMACs (does it fit)
- 128k elements = 17-bit address path
- rs1 = 2x4-bit masks + 17-bit address
- rs2 = 2x16-bit strides
How to run a RISC-V test:
You can run a risc-v test (source code available in firmwares) by:
./simulate.sh firmwares/add.hex