I2S and S/PDIF

Digital audio interfaces: I2S, S/PDIF, PDM microphones.

Core	Repository	Language	License	FPGA	Used by
I2S audio interface (ulx3s-misc) ★	emard__ulx3s-misc	VHDL (wrapper), Verilog	BSD (`-- AUTHOR=EMARD` / `-- LICENSE=BSD` header)	any	1
AK4619 audio codec driver + PMOD I2C master	apfaudio__eurorack-pmod	SystemVerilog	CERN-OHL-S-2.0	any	0
Cynthion USB Audio Class 2.0 example	greatscottgadgets__cynthion-uac	Python (Amaranth)	BSD-3-Clause	ECP5	1
I2S receiver (orangecrab-usb)	mangelajo__orangecrab-usb	Verilog	none found	any	0
I2S RX/TX + PDM/CIC mic front-end (sound2fft)	mebner86__icesugar-pro_sound2fft	Verilog	MIT (LICENSE, repo root)	ECP5	0
S/PDIF transmitter (f32c)	f32c__f32c	VHDL	BSD-2-Clause	any	0
S/PDIF transmitter (synthowheel)	emard__synthowheel	VHDL	BSD (LICENSE.txt: AUTHOR=EMARD LICENSE=BSD)	any	12

Cores

I2S audio interface (ulx3s-misc) (best)

Parametric I2S transmit core (fmt/clk_hz/lrck_hz generics) demonstrated in the ULX3S audio example, VHDL wrapper over a Verilog core.


Repository	emard__ulx3s-misc: ULX3S misc/advanced examples: EMARD’s building-block library
Files	`examples/audio/hdl/i2s.vhd`, `examples/audio/hdl/i2s_v.v`
Top module	`i2s`
Language	VHDL (wrapper), Verilog
License	BSD (`-- AUTHOR=EMARD` / `-- LICENSE=BSD` header)
FPGA / primitives	any: none (portable)
Tests	waveform-only (testbench/sinewave.c is a non-HDL C reference model)

On ULX3S: clk_hz=25000000 matches the ULX3S board oscillator; see examples/audio/hdl/top_audio.v for a complete instantiation.

Full review: emard__ulx3s-misc.

Used by 1 other catalogued repo (file copies or module instances found by scan_core_usage.py; heuristic):

f32c__f32c (copies rtl/soc/i2s_v.v)

AK4619 audio codec driver + PMOD I2C master

Configures an AK4619 4in/4out audio codec over I2C at boot, then streams 8 audio channels (192kHz/32-bit capable) in/out on a clk_256fs+strobe interface; used on every Eurorack PMOD board target (ECPIX-5, Colorlight, Tiliqua, iCEBreaker, iCESugar, Pico-Ice, GateMate).


Repository	apfaudio__eurorack-pmod: Eurorack PMOD: AK4619 audio-codec PMOD gateware
Files	`gateware/drivers/ak4619.sv`, `gateware/drivers/pmod_i2c_master.sv`
Top module	`ak4619`
Language	SystemVerilog
License	CERN-OHL-S-2.0 (repo-level LICENSE; no per-file header)
FPGA / primitives	any: none (portable)
Tests	cocotb, e.g. gateware/sim/ak4619/tb_ak4619.py - self-checking (@cocotb.test() assertions)

On ULX3S: No vendor primitives; needs the Eurorack PMOD hardware (or another AK4619-based codec board) wired to a PMOD/I2S+I2C header. Pair with cal/cal.sv for jack-detect calibration.

Cynthion USB Audio Class 2.0 example

Full USB Audio Class 2.0 device (descriptors, isochronous streaming, feedback-endpoint clock recovery via clockgen.py) driving an internally synthesized stereo sine wave (NCO + LUT) instead of a real codec; includes a VU meter. No I2S/S-PDIF pins are used - audio never leaves the FPGA.


Repository	greatscottgadgets__cynthion-uac: cynthion-uac: official USB Audio Class 2.0 example gateware for Cynthion
Files	`uac/top.py`, `uac/uac2.py`, `uac/dac.py`, `uac/dsp.py`, `uac/nco.py`
Top module	`USBAudioClass2Device`
Language	Python (Amaranth)
License	BSD-3-Clause (repo LICENSE.txt); uac/dac.py under a separate ISC-style permission notice (adapted from the Glasgow Interface Explorer audio applet)
FPGA / primitives	ECP5: none (portable)
Tests	none found

On ULX3S: Runs on Cynthion’s target_phy ULPI port out of the box (python -m uac.top, needs the cynthion package installed); to drive a real DAC, replace dac.py’s Channel sink with actual I2S/PDM output pins.

Used by 1 other catalogued repo (file copies or module instances found by scan_core_usage.py; heuristic):

antoinevg__cynthion-tutorials (instantiates examples/uac/step-1.py)

I2S receiver (orangecrab-usb)

Small I2S receiver: deserializes left/right 32-bit channel data from an external I2S codec given a 64fs input clock.


Repository	mangelajo__orangecrab-usb: OrangeCrab: two USB device examples
Files	`hdl/i2s/i2s.v`
Top module	`i2s`
Language	Verilog
License	none found (repo has no LICENSE/COPYING file)
FPGA / primitives	any: none (portable)
Tests	none found

On ULX3S: Plain Verilog, portable; pairs with hdl/clkdiv/clkdiv.v in the same repo for MCLK/BCLK generation.

I2S RX/TX + PDM/CIC mic front-end (sound2fft)

I2S receiver/transmitter plus a PDM-microphone CIC decimator and PDM modulator, part of a cocotb bit-exact-tested audio+FFT+HDMI pipeline for iCESugar-Pro (ECP5 25F).


Repository	mebner86__icesugar-pro_sound2fft: iCESugar-Pro sound2fft: real-time audio spectrum analyzer
Files	`rtl/i2s_rx.v`, `rtl/i2s_tx.v`, `rtl/pdm_cic.v`, `rtl/pdm_modulator.v`
Top module	`i2s_rx`
Language	Verilog
License	MIT (LICENSE, repo root)
FPGA / primitives	ECP5: none (portable)
Tests	cocotb, bit-exact vs numpy (per repo README; test scripts not individually re-verified here)

On ULX3S: Portable front-end; only the TMDS serializer elsewhere in the repo needs ECP5 ODDRX1F, not these audio blocks.

S/PDIF transmitter (f32c)

Same ackspace.nl-derived S/PDIF transmitter as synthowheel’s, vendored into the f32c SoC’s peripheral set.


Repository	f32c__f32c: f32c: retargetable RISC-V/MIPS 32-bit soft CPU + SoC library
Files	`rtl/soc/spdif_tx.vhd`
Top module	`spdif_tx`
Language	VHDL
License	BSD-2-Clause (repo-level per docs/projects/f32c__f32c.md; file itself carries no SPDX header, same ackspace.nl/EMARD-derived source)
FPGA / primitives	any: none (portable)
Tests	none found

On ULX3S: Used from the f32c SoC’s audio/CPU bus glue; can be lifted standalone like the synthowheel copy.

Full review: f32c__f32c.

S/PDIF transmitter (synthowheel)

S/PDIF biphase-mark transmitter, derived from the ackspace.nl SPDIF project with EMARD’s clock-divider modification; 24-bit signed PCM in, 25 MHz/48 kHz defaults.


Repository	emard__synthowheel: Synthowheel: polyphonic additive synth, 128 gen x 9 harmonics, SPDIF + sigma-delta
Files	`spdif_tx.vhd`
Top module	`spdif_tx`
Language	VHDL
License	BSD (LICENSE.txt: AUTHOR=EMARD LICENSE=BSD)
FPGA / primitives	any: none (portable)
Tests	none found

On ULX3S: C_clk_freq=25000000 matches the ULX3S oscillator directly; single-bit spdif_out needs a coax/TOSLINK line driver off-board.

Used by 12 other catalogued repos (file copies or module instances found by scan_core_usage.py; heuristic):

dan-rodrigues__icestation-32 (instantiates hardware/ulx3s/ics32_top_ulx3s.v)
dan-rodrigues__ics-adpcm (instantiates demo/adpcm_demo_top.v)
emard__fpga_snake_game (copies rtl_emard/spdif/spdif_tx.vhd)
emard__minimig_ecs (instantiates proj/altera/ffm-c5a4-sd-lcdif/top/amiga_ffm_c5a4_sd.vhd)
emard__papilio-arcade (instantiates pacman_rel004_sp3e_papilio/proj/lattice/ulx3s/pacman_ulx3s_v20_12f/top/pacman_ulx3s.vhd)
emard__uk101onfpga (copies rtl_emard/spdif/spdif_tx.vhd)
emard__ulx3s-misc (instantiates examples/audio/hdl/top_audio.v)
emard__ulx3s_c64 (instantiates rtl/top_ulx3s_v20_c64.vhd)
emard__vhdl_c64_c1541_sd (instantiates proj/lattice/ulx3s/top/c64_ulx3s.vhd)
emard__vhdl_phoenix (instantiates proj/lattice/ulx3s/top/phoenix_ulx3s.vhd)
f32c__f32c (instantiates rtl/generic/glue_xram.vhd)
linuxjedi__minimig_ecs (instantiates proj/altera/ffm-c5a4-sd-lcdif/top/amiga_ffm_c5a4_sd.vhd)

Other catalogued projects

Catalogued repos tagged audio-i2s (19), audio-spdif (8) are listed in the full catalogue.