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Experimenting with writing a simple processor in Calyx

This is a bad implementation of a subset of the RISCV32-I instruction set.

Reasons this is bad (and thus areas to improve)

  • This implementation is not pipelined, meaning that each instruction takes ~18 cycles to execute
  • I haven’t used static anywhere. I think that most things can probably be made static
  • I haven’t made any particular effort to simplify decoding logic
  • probably more things

Simulating a RISC-V assembly file

I have provided a fud2 stage to make this process simpler. Start by installing the plugin. Add the following line to your fud2.toml config file.

plugins = [
  "<calyx-riscv root>/fud2/riscv.rhai"
]

You will also want to set the riscv.exe variable either in your config or on the command line. Here’s what the config looks like.

[riscv]
exe = "<path to riscv-to-calyx binary>"
# for development on riscv-to-calyx
# exe = "cargo run --manifest-path=<path to riscv-to-calyx Cargo.toml>"

You will need riscv64-unknown-elf-as installed. If the binary isn’t located on the path, you can specify it’s location in fud2.toml under the variable riscv.assembler.

You should be able to see riscv-simulate and riscv-decode operations in the output of fud2 list.

To simulate the riscv-to-calyx/data/simple.s file, you can run

fud2 riscv-to-calyx/data/simple.s --to riscv-decode

This should have the following output:

Took 1227 cycles

== instructions ==
  0: addi x10, x0, 0
  1: addi x11, x0, 10
  2: addi x5, x0, 0
  3: addi x6, x0, 0
  4: bge x6, x11, 1c
  5: slli x7, x6, 2
  6: add x7, x10, x7
  7: lw xxx
  8: add x5, x5, x7
  9: addi x6, x6, 1
 10: J { opcode: 111, rd: 0, imm: 1042943 }
 11: addi x10, x5, 0
 12: I { opcode: 103, rd: 0, funct3: 0, rs1: 1, imm: 0 }

== registers ==
x0  zero: 0
x1    ra: xxxxxxxx
x2    sp: xxxxxxxx
x3    gp: xxxxxxxx
x4    tp: xxxxxxxx
x5    t0: 10
x6    t1: 10
x7    t2: 1
x8    fp: xxxxxxxx
x9    s1: xxxxxxxx
x10    a0: 10
x11    a1: 10
x12    a2: xxxxxxxx
x13    a3: xxxxxxxx
x14    a4: xxxxxxxx
x15    a5: xxxxxxxx
x16    a6: 0
x17    a7: 0
x18    s2: 0
x19    s3: 0
x20    s4: 0
x21    s5: 0
x22    s6: 0
x23    s7: 0
x24    s8: 0
x25    s9: 0
x26   s10: 0
x27   s11: 0
x28    t3: 0
x29    t4: 0
x30    t5: 0
x31    t6: 0

Note:

This command assumes that both the fud and calyx-py python packages are installed in the environment that you are running this in. With the annoying new pip restrictions, this is more annoying than ever.

To do this the “proper” way, you can run the following commands:

# create a new venv inside the root of this repo
cd calyx-riscv
python3 -m venv .

# acitvate the venv
source bin/activate

# install dependencies through flit
pip3 install flit
cd ../calyx/fud
python3 -m flit install # make sure to use the flit inside of the venv
cd ../calyx-py
python3 -m flit install