pdm_mic_demo Directory Reference

Directory dependency graph for pdm_mic_demo:

Directories
	src

Detailed Description

Captures from the EK-RA8D2's on-board PDM MEMS microphones through the ra8_audio facade and its ra8_pdm backend, then judges whether what came back is plausibly acoustic. Closes gap issue #129.

The verdict is the point. It captures 20-bit PCM windows and reports RMS, peak, mean and span, calling the line active only when a window is non-degenerate – not a stuck DC constant, not all zero – and carries plausible energy. A dead mic line reads as inactive; a PDM clock that never toggles leaves the FIFO empty and says so. That is a distinction "did the driver return ok?" cannot make. After the terminal verdict the firmware parks in a low-power wait so the bench and the emulator observe one stable result, and the verdict is also latched in the J-Link-probable global g_pdm_mic_result.

Hardware

Two SPH0690LM4H-1 PDM MEMS microphones sit on the underside of the PCB. No external hardware is required.

SPH0690 pin	Signal	EVM net	MCU function
1 (DATA)	PDM data	P502	PDMDAT2 (PSEL 0x1B)
4 (CLOCK)	PDM clock	P812	PDMCLK2 (PSEL 0x1B)
2 (SELECT)	L/R sel	GND (MIC1) / +3.3V (MIC2)	rise / fall edge

Both mics share the single clock and data line (standard PDM stereo), so both land on PDM-IF channel 2 and INPSEL chooses between them by clock edge – INPSEL=0 selects the rise-edge mic, MIC1 with SELECT tied to GND. Pin assignments follow EK-RA8D2 v1 UM Table 31 p 37 and the RA8D2 datasheet pin functions for P502 / P812.

Signal path (all hardware, HUM Ch 49)

PDMIFCLK = MOCO 8 MHz
  -> PDM_CLK2 = 8 MHz / (2*(CKDIV+1)) = 4 MHz          (CKDIV=0)
  -> 4th-order sinc decimation, M = SINCDEC+1 = 125     (SINCDEC=0x7C, SINCRNG=0x05)
  -> compensation FIR -> high-pass (DC block) -> half-band /2
  -> Fout = 4 MHz / (2*125) = 16 kHz, 20-bit signed PCM (PDDRRCH2)

That decimation combination is a HUM Table 49.7 row (order 4). The filter coefficients are the RA8D2 reset defaults for this microphone family (HUM Ch 49.2 register reset values), owned by the board's PDM adapter rather than by this app.