Audio Capture

PDM microphone capture with RMS/peak statistics streamed over SWO.

Declared by the example author	Value
Tier	Capabilities
Status	tested
Capabilities	audio, pdm
Boards tested	apollo510_evb

Build it from a source checkout by name, because the positional app argument resolves under ./examples:

nsx build audio_capture --board apollo510_evb

The rest of this page is the example’s own README, from examples/audio_capture/.

Demonstrates nsx-audio on the Apollo510 EVB. Configures the PDM microphone at 16 kHz, captures 30 ms audio frames, and prints peak amplitude to SWO every 100 frames (~3 seconds).

Build & Run

nsx configure --app-dir .
nsx build     --app-dir .
nsx flash     --app-dir .      # requires EVB with onboard PDM mic
nsx view      --app-dir .      # opens SWO viewer

Expected Output

The SWO viewer will print once at startup, then peak amplitude every 100 frames (~3 s at 16 kHz / 480 samples per frame):

Audio capture started: 16000 Hz, 1 ch, 480 samples/frame
Frame 100  peak=1842
Frame 200  peak=2105
Frame 300  peak=947
Frame 400  peak=3210

Peak values depend on ambient noise. Silence gives values near 0; speaking near the mic gives values in the thousands (int16 range).

How It Works

1. Configures the PDM peripheral at 16 kHz mono via nsx_audio_init()
2. DMA transfers 480-sample (30 ms) frames into a ping-pong buffer
3. A callback fires per frame; the main loop computes peak amplitude
4. DMA buffers use NSX_MEM_SRAM_BSS placement — the DMA engine on Apollo5 cannot access TCM

Hardware Notes

• The Apollo510 EVB has an onboard PDM MEMS microphone
• No additional hardware or wiring is needed
• PDM clock and data pins are set by the EVB board definition