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Playing at the console's sample rate on the Retroid Pocket Nova

How PortareOS makes the Nova's audio link run at 32, 44.1 or 48 kHz instead of resampling everything to 48 kHz, and how to carry that to another distribution. Everything here was verified on the device (kernel 7.2.5, September 2026).

The Nova's audio is Qualcomm AudioReach: a DSP graph, MI2S to two aw88166 speaker amps, and a codec DMA path to the WCD938x headphone codec. Four things pin playback to 48 kHz, in the order a request meets them:

  1. The topology blob (qcom/sm8550/AYN-Odin2-tplg.bin) declares the playback PCMs' capabilities: rates = 0, rate_min = rate_max = 48000. The frontend is constrained to that before any kernel code sees the request. A 32 kHz request is answered with the nearest allowed rate (Warning: rate is not accurate (requested = 32000Hz, got = 44100Hz)) and nothing in dmesg says why. Without this step, the kernel patches below change nothing.
  2. The DAI rate masks in sound/soc/qcom/qdsp6/q6dsp-lpass-ports.c. The speaker port, PRIMARY_MI2S_RX, is written out longhand with 48000 | 8000 | 16000 only; the headphone port uses the CDC-DMA macro, which lacks 44100.
  3. The machine driver's fixup, sc8280xp_be_hw_params_fixup() in sound/soc/qcom/sc8280xp.c, which pins every backend to 48000 and S16_LE stereo. With only the masks widened, the DSP resamples instead.
  4. The I2S bit clock, LPASS_CLK_ID_SEN_MI2S_IBIT, fixed by the device tree (assigned-clock-rates = <1536000>, that is 48000 × 2 × 16) and enabled at startup. The link runs at a 48 kHz bit clock whatever the sample rate.

The headphone path (codec DMA) has no bit clock of its own and needs only steps 1 to 3.

The changes, in order

All paths are in this repository; the patches apply to Linux 7.2.5.

1. The topology blob

packages/linux-firmware/extra-firmware/sources/tplg-playback-rates.py, run by extra-firmware's package.mk on the shipped blob.

The blob is ALSA topology: a sequence of blocks with a 36-byte header (magic 0x41536F43, ABI, version, type, header size, vendor type, payload size, index, count). In each block of type 7 (PCM), every PCM record holds a name at offset 4, playback and capture flags at offset 100, and, after the 8 stream records of 72 bytes, a capability block whose rates, rate_min and rate_max sit at offset 56. The script finds the playback PCMs (MultiMedia1 Playback and MultiMedia2 Playback), sets rates = SNDRV_PCM_RATE_32000 | 44100 | 48000 (bits 5, 6 and 7), rate_min = 32000, rate_max = 48000, and leaves capture alone. It checks the input hash and the output hash, so a different blob is refused rather than mis-edited.

Rebuilding the blob from the AudioReach topology source was tried first; the available .m4 does not reproduce the shipped binary, hence the in-place edit.

2. Kernel patches (projects/PortareOS/devices/SM8550/patches/linux/)

Patch File What it does
1052-…-allow-44100-on-the-rx-dais q6dsp-lpass-ports.c Adds 44100 to the MI2S and CDC-DMA RX macros and to the longhand Primary MI2S Playback entry.
1053-…-allow-44100-backends sc8280xp.c In the backend fixup, keeps the frontend's rate when it is exactly 44100 on PRIMARY_MI2S_RX and RX_CODEC_DMA_RX_0; every other backend stays pinned (DISPLAY_PORT_RX_0 offers only 48/96/192 kHz).
1054-…-mi2s-bit-clock-from-stream sc8280xp.c In the machine prepare, sets the MI2S bit clock to rate × channels × width. A q6dsp clock only reports its rate to the DSP when prepared, and startup has already prepared it, so on a rate change the clock is unprepared, set and prepared again; otherwise the port starts on the previous stream's clock and the DSP refuses APM_CMD_GRAPH_START. Done in prepare, before DAPM PRE_PMU, because the aw88166 amps check their PLL against BCLK there.
1055-…-allow-32000-playback both 32000 in the Primary MI2S Playback mask, and 32000 let through the fixup on the two playback ports.

Two earlier patches matter for the amps: 0036 (Primary I2S support in the machine driver, including the i2s_clk handling) and 0612 (start the RX port at prepare, so BCLK is up before the amps' PLL check).

3. PipeWire

packages/audio/pipewire/patches/SM8550/002-graph-quantum.patch: default.clock.allowed-rates = [ 48000 44100 32000 ]. PipeWire then switches the graph, and the link, to the rate of the stream that opens it.

4. Applications

RetroArch picks the output rate from the core's when audio_out_rate is "0" (patch 0015-audio-out-rate-from-the-core.patch): the smallest of 32000, 44100 and 48000 the core's rate divides into within 0.5 %, else the smallest above it, else 48000, re-picked at every audio init so a core that changes rate mid-session (ParaLLEl N64, per game) reopens the device to match. A non-zero audio_out_rate in a per-core config (config/<core>/<core>.cfg) overrides the pick. mpv plays at the file's rate, for films and for PORTAMP alike. REFRESH_RATES.md has the table.

Verifying on the device

# What the frontend allows. Before the blob edit this printed [44100 48000].
aplay -D hw:0,0 --dump-hw-params -f S16_LE -c 2 -r 48000 -d 0 /dev/zero 2>&1 | grep ^RATE

# A request at the rate, without the "not accurate" warning:
aplay -D hw:0,0 -f S16_LE -c 2 -r 32000 -d 1 /dev/zero

# While something plays: the link rate, the bit clock, and the DSP's verdict.
grep ^rate /proc/asound/card0/pcm0p/sub0/hw_params        # rate: 32000 (32000/1)
cat /sys/kernel/debug/clk/LPASS_CLK_ID_SEN_MI2S_IBIT/clk_rate  # 1024000 = 32000 x 2 x 16
dmesg | grep -i "bit clock\|APM_CMD"                        # must stay empty

Then switch rates in a row (48 → 32 → 44.1 → 48) and check that each stream starts. aplay -D hw:0,0 bypasses PipeWire and its volume control: the tone will be loud.

Testing a blob without rebuilding the image

The blob is not built into the kernel (CONFIG_EXTRA_FIRMWARE carries only the regulatory database), so it is loaded from /lib/firmware when the sound card binds, and /lib/firmware is a writable tmpfs of symlinks into the kernel overlay:

systemctl stop pipewire-pulse.service pipewire.service wireplumber.service pipewire.socket pipewire-pulse.socket
rm /lib/firmware/qcom/sm8550/AYN-Odin2-tplg.bin
cp /tmp/AYN-Odin2-tplg.bin /lib/firmware/qcom/sm8550/
echo sound > /sys/bus/platform/drivers/snd-sc8280xp/unbind
echo sound > /sys/bus/platform/drivers/snd-sc8280xp/bind
systemctl start pipewire.socket pipewire-pulse.socket pipewire.service wireplumber.service pipewire-pulse.service

The topology is loaded in the qcom-apm component's probe, which runs on card bind. A reboot restores the shipped blob.

Porting to another distribution

  • Take the four kernel patches as they are; they touch only q6dsp-lpass-ports.c and sc8280xp.c. The bit-clock name and the assigned-clock-rates come from the board's device tree; check the sound node.
  • Apply the topology edit to your copy of the blob. If the hash differs from the one in the script, the blob is a different build: read the PCM blocks and check the offsets before editing, and record both hashes.
  • Add the rates to PipeWire's allowed-rates, or to whatever your sound server uses to pick the device rate.
  • Ask for the rate per application. A global 44.1 kHz would only move the resampling for everything else.

Not viable: rates the hardware cannot carry, such as an exact 32040 (the SNES's) or 32768 (the Game Boy's). The headphone codec has no rate code for them, and the DSP's endpoints and clock table only offer the standard rates. portare-ch/portareos#290 has the analysis.