102 Silly-Faust
102 : Silly-Faust
- Author: Louis Ledoux, Cochard Pierre
- Description: Trial to use the audio circuit compiler for open silicon
- GitHub repository
- Open in 3D viewer
- Clock: 44100 Hz
How it works
TTGF0P2 compiles the one-line Faust soft clipper softclip(x) = tanh(3x) / tanh(3) into silicon.
The flow snapshots every MLIR stage in src/20251113-120748-faust-tanh-softclip-switchcase/stages, which mirrors the pipeline below:
- Stage 00 – Faust frontend. Capture the canonical Faust AST with
faust.graphops. - Stage 10 – Real arithmetic.
--faust-to-core-real-arith --configure-faust-real-arith="config=hls-driver/pipelines/tanh-softclip-8bit-config.json"tags the input domain[-1, 1]and keeps the DSP in symbolic real form. - Stage 20 – Uniform piecewise fixed-point.
--realarith-to-fixed_pt_arithsubdivides the domain into eight regions, emits Horner coefficients per region, and keeps all truncations explicit. - Stage 30 – FixedPointArith to Arith.
--fixed_pt_arith-to-arithrewrites everything intoarith+scfso the datapath is purely integer. - Stage 40/50/55 – Switch normalization and CF prep.
--switch-to-if,--convert-scf-to-cf, and--strip-real-arith-arg-attrssanitize control flow before Dynamatic lowers the result to handshake/RTL.
The resulting RTL lives in src/faust_core.v and is wrapped by tt_um_gf0p2_faust_top, which multiplexes between an internal ramp and the external sample bus. ui_in[0] selects the source (0 = internal ramp, 1 = external data on ui_in[7:1]), and the 8-bit result appears on uo_out, ready to drive an R-2R ladder.
How to test
- Install the Python requirements (
pip install -r test/requirements.txt). - Run
make -C testfor the full Cocotb suite ormake -C test simfor the Icarus-only path. - Inspect
test/results.xmlortest/tb.vcdfor pass/fail information and waveforms.
The regression toggles between the internal ramp and external stimulus to ensure the Horner pipeline matches the saved MLIR snapshots.
External hardware
- Attach the 8-bit Tiny Tapeout DAC (or Digilent Pmod R-2R) to
uo[7:0]for line-level audio. - Provide an optional external 7-bit sample stream on
ui[7:1](MSB onui[7]) and raiseui[0]to route it through the Faust core. - Keep every
uiopin unconnected; they remain inputs inside the design.
The Pmod R-2R documentation: https://digilent.com/reference/pmod/pmodr2r/start
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | src_sel (0=ramp,1=external) | dac_out[0] | nc (input only) |
| 1 | ext_sample[0] | dac_out[1] | nc (input only) |
| 2 | ext_sample[1] | dac_out[2] | nc (input only) |
| 3 | ext_sample[2] | dac_out[3] | nc (input only) |
| 4 | ext_sample[3] | dac_out[4] | nc (input only) |
| 5 | ext_sample[4] | dac_out[5] | nc (input only) |
| 6 | ext_sample[5] | dac_out[6] | nc (input only) |
| 7 | ext_sample[6] (MSB) | dac_out[7] (MSB) | nc (input only) |