Spectrum meter levels computed in the UAC pump task - #50
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uac_pump_meter(bands, lo_hz, hi_hz) turns on band levels computed where the sound card's bytes already pass: the C pump feeds each block it reads to usbif_meter.c, which runs two FFTs about 60 times a second (1024 points at the host rate for the upper bands, 512 points on a 700 Hz low-passed copy decimated by 16 for the bottom) and publishes one byte per band in half-dB steps. uac_pump_levels([buf]) reads them under a sequence lock; with no arguments uac_pump_meter() returns its cost counters. Also moves the audio receive path (TinyUSB's DWC2 driver, usbd, the audio class and its FIFO, and usbif's ISR hook) into IRAM with a linker fragment. On its own that made no measurable difference to delivery; it stays because the spike's numbers were taken with it.
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uac_pump_meter(bands, lo_hz, hi_hz)anduac_pump_levels([buf]): band levels computed where the sound card's bytes already pass. The C pump feeds each block it reads tousbif_meter.c, which runs two FFTs about 60 times a second and publishes one byte per band in half-dB steps.uac_pump_meter()with no arguments returns its cost counters.It's the C half of the spectrum example (pydevices-examples
lib/examples/spectrum,pump_levels.py). Proven on the ESP32-P4 panel on 2026-09-25, beside the sound card: the pump costs about 1 % of a 360 MHz core for the feed, and meter-on and meter-off USB delivery match to within 0.03 % once the panel's cache writeback is sliced. That setting landed as micropython-pydevices#23.Not proven: an S3 build and run with the meter compiled in. The spike only ran on the P4.