PDM MEMS microphone capture + plausibility demo (SPH0690 / ch 2). More...

#include <stdint.h>
#include "ra8_audio.h"
#include "ra8_audio_source_pdm.h"
#include "ra8_board_ek_ra8d2.h"
#include "ra8_boot_entry.h"
#include "ra8_err.h"
#include "ra8_mstp.h"
#include "ra8_time.h"

Include dependency graph for main.c:

Data Structures
struct	pdm_metrics_t
	Statistics for one captured PCM window. More...
struct	pdm_mic_result_t
	Debugger-probable capture result. More...

Enumerations
enum	pdm_demo_const_t : uint32_t { k_pdm_demo_baud = 115200U , k_pdm_demo_decimal = 10U , k_pdm_demo_settle_ms = 300U , k_pdm_demo_window = 256U , k_pdm_demo_discard = 1024U , k_pdm_demo_report_win = 8U , k_pdm_demo_poll_max = 500000U }
	App-wide tunables. More...
enum	pdm_demo_threshold_t : int32_t { k_pdm_demo_min_span = 8 , k_pdm_demo_rms_floor = 16 }
	Plausibility thresholds (20-bit signed full scale = +-524288). More...
enum	pdm_demo_str_cap_t : uint32_t { k_pdm_demo_int_str_cap = 12U }
	Sizing for the decimal serialiser buffer ("-2147483648" + NUL). More...
enum	pdm_isqrt_const_t : uint32_t { k_pdm_isqrt_steps = 32U , k_pdm_isqrt_top2 = 62U }
	Integer-sqrt bit-window constants (64-bit radicand). More...
enum	pdm_demo_magic_t : uint32_t { k_pdm_demo_magic = 0x50444D31U }
	Result magic marker ('PDM1'). More...

Functions
static void	pdm_demo_panic_halt (void)
	Park forever after a fatal error.
static uint32_t	pdm_demo_i32_to_dec (int32_t value, uint8_t *out)
	Convert a signed 32-bit int into a decimal ASCII string.
static uint32_t	pdm_demo_isqrt (uint64_t value)
	Integer square root of a 64-bit value (floor).
static void	pdm_demo_tx (const uint8_t *bytes, uint32_t len)
	Emit a byte run over the SCI8 console.
static void	pdm_demo_emit_kv (const uint8_t *label, uint32_t label_len, int32_t value)
	Emit "<label><value>" with a decimal integer.
static void	pdm_demo_clocks_or_halt (void)
	Bring CGC + MSTP + SysTick up; halts on any failure.
static void	pdm_demo_io_or_halt (void)
	Route P812/P502 to the PDM function and open the console.
static void	pdm_demo_pdm_or_halt (void)
	Bind the on-board MIC1 through the reusable PDM audio source.
static void	pdm_demo_analyze (const int32_t buf, uint32_t n, pdm_metrics_t m)
	Compute min/max/mean/peak/RMS for a captured window.
static bool	pdm_demo_is_active (const pdm_metrics_t *m)
	Decide whether a window carries plausible live audio.
static void	pdm_demo_publish (const pdm_metrics_t *m, int32_t vary, bool active)
	Print a per-window detail line and latch g_pdm_mic_result.
static bool	pdm_demo_run_window (int32_t vary, pdm_metrics_t *out_m)
	Capture one window, analyse it and publish it.
void	main (void)
	Application entry: bring up the PDM mic and report plausibility.

Variables
volatile pdm_mic_result_t	g_pdm_mic_result
	J-Link-probable capture result (read at &g_pdm_mic_result).
static int32_t	s_pdm_demo_buf [k_pdm_demo_window]
	Static capture buffer (kept off the stack).
static ra8_audio_source_t	s_pdm_demo_source
	Generic caller-owned audio source handle.
static ra8_audio_source_pdm_state_t	s_pdm_demo_source_state
	Caller-owned PDM backend state.
static const uint8_t	k_pdm_demo_banner_init [] = "pdm: init ch=2 clk=4mhz fs=16khz\r\n"
static const uint8_t	k_pdm_demo_banner_fail [] = "pdm: init FAIL\r\n"
static const uint8_t	k_pdm_demo_banner_nodat [] = "pdm: no data (FIFO empty) -- clock/mic?\r\n"
static const uint8_t	k_pdm_demo_banner_pass [] = "pdm: verdict=PASS active=Y\r\n"
static const uint8_t	k_pdm_demo_banner_inactive [] = "pdm: verdict=FAIL active=N\r\n"

Detailed Description

PDM MEMS microphone capture + plausibility demo (SPH0690 / ch 2).

Tag: [Ring 6 / APP] {World: S}

Stand-alone EK-RA8D2 application that brings up the on-board SPH0690 PDM MEMS microphones and reports whether they produce plausible audio.

Board wiring (EK-RA8D2 v1 UM Table 31 p 37): two SPH0690 mics (MIC1, MIC2) on the PCB underside share one clock and one data line ->

PDMCLK2 = P812 (MIC pin 4, CLOCK)
PDMDAT2 = P502 (MIC pin 1, DATA) MIC1 SELECT = GND (rise-edge data), MIC2 SELECT = +3.3V (fall-edge). Both are on PDM-IF channel 2, so this demo captures MIC1 (rise edge).

Signal path (all in hardware, HUM Ch 49): 4 MHz PDM_CLK2 (PDMIFCLK = MOCO 8 MHz / 2) -> 4th-order sinc decimation (M=125) -> compensation FIR -> high-pass (DC block) -> half-band decimation -> 16 kHz, 20-bit signed PCM read out of PDDRRCH2. Filter coefficients are the RA8D2 reset-default SPH0690 set (HUM Ch 49.2 register reset values).

Flow:

Board clocks / ra8_mstp_init / ra8_time_init.
Route P812/P502 to the PDM function; bring up the SCI8 console.
Query board-owned SPH0690 policy and bind ra8_audio_source_pdm.
The backend starts PDM-IF, settles, and discards the filter transient.
Capture caller-owned fixed-size PCM frames through ra8_audio.
Compute AC RMS / peak / span and a plausibility verdict, print the banner pdm: rms=NNN peak=NNN active=Y (scraped by hil.conf) and publish it in the J-Link-probable g_pdm_mic_result.
Latch the PASS verdict and park in a low-power wait loop.

Copyright: Copyright (c) 2026 Brighton Sikarskie SPDX-License-Identifier: MIT

Since: 0.1.0

Definition in file main.c.

Enumeration Type Documentation

◆ pdm_demo_const_t

enum pdm_demo_const_t : uint32_t

App-wide tunables.

Enumerator
k_pdm_demo_baud	SCI8 console baud.
k_pdm_demo_decimal	Radix for integer-to-ASCII.
k_pdm_demo_settle_ms	Mic wake-up + filter settle delay.
k_pdm_demo_window	PCM samples per analysis window.
k_pdm_demo_discard	Transient samples discarded up front.
k_pdm_demo_report_win	Windows swept for the verdict banner.
k_pdm_demo_poll_max	Bounded capture poll retries (dead-mic).

Definition at line 57 of file main.c.

◆ pdm_demo_magic_t

enum pdm_demo_magic_t : uint32_t

Result magic marker ('PDM1').

Enumerator
k_pdm_demo_magic	Pdm demo magic.

Definition at line 135 of file main.c.

◆ pdm_demo_str_cap_t

enum pdm_demo_str_cap_t : uint32_t

Sizing for the decimal serialiser buffer ("-2147483648" + NUL).

Enumerator
k_pdm_demo_int_str_cap	Pdm demo int str cap.

Definition at line 74 of file main.c.

◆ pdm_demo_threshold_t

enum pdm_demo_threshold_t : int32_t

Plausibility thresholds (20-bit signed full scale = +-524288).

Enumerator
k_pdm_demo_min_span	Min peak-to-peak to be non-degenerate.
k_pdm_demo_rms_floor	Min AC RMS to count as live audio.

Definition at line 68 of file main.c.

◆ pdm_isqrt_const_t

enum pdm_isqrt_const_t : uint32_t

Integer-sqrt bit-window constants (64-bit radicand).

Enumerator
k_pdm_isqrt_steps	32 two-bit steps span a 64-bit radicand.
k_pdm_isqrt_top2	Shift to the top 2 bits of a 64-bit word.

Definition at line 79 of file main.c.

Function Documentation

◆ main()

void main ( void )

Application entry: bring up the PDM mic and report plausibility.

The application entry point Reset_Handler hands control to.

Precondition: Reset_Handler has copied .data and zeroed .bss.; SystemInit has set VTOR, FPU and priority grouping.

Postcondition: The verdict banner is printed and remains the terminal UART line.; g_pdm_mic_result carries the validated capture result.

Since: 0.1.0

Definition at line 610 of file main.c.

References g_pdm_mic_result, k_pdm_demo_banner_inactive, k_pdm_demo_banner_pass, k_pdm_demo_report_win, pdm_demo_clocks_or_halt(), pdm_demo_io_or_halt(), pdm_demo_panic_halt(), pdm_demo_pdm_or_halt(), pdm_demo_run_window(), pdm_demo_tx(), and pdm_metrics_t::rms.

◆ pdm_demo_analyze()

void pdm_demo_analyze	(	const int32_t *	buf,
		uint32_t	n,
		pdm_metrics_t *	m )

static

Compute min/max/mean/peak/RMS for a captured window.

Two bounded passes: pass 1 accumulates min/max/mean; pass 2 accumulates the AC peak and mean-square about that mean. A zero-sample window is rejected before either pass runs, so a source that reports an empty capture cannot divide by zero.

Parameters

[in]	buf	Sample buffer (non-NULL).
[in]	n	Sample count.
[out]	m	Metrics output (non-NULL).

Returns: Nothing.

Precondition: buf holds n valid samples.; m is non-NULL.

Postcondition: n == 0 leaves *m entirely zeroed.; n > 0 leaves m->rms and m->peak non-negative.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 439 of file main.c.

References pdm_metrics_t::max, pdm_metrics_t::mean, pdm_metrics_t::min, pdm_metrics_t::n, pdm_demo_isqrt(), pdm_metrics_t::peak, and pdm_metrics_t::rms.

Referenced by pdm_demo_run_window().

◆ pdm_demo_clocks_or_halt()

void pdm_demo_clocks_or_halt ( void )

static

Bring CGC + MSTP + SysTick up; halts on any failure.

Runs on MOCO (~8 MHz), which also sources PDMIFCLK (8 MHz).

Returns: Nothing.

Precondition: Reset_Handler prepared .data/.bss.; Single-threaded init context.

Postcondition: CGC, MSTP and the delay timer are live on success.; The CPU is parked on any failure.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 331 of file main.c.

References ra8_board_clock_rates_t::cpuclk0_hz, k_ra8_ok, pdm_demo_panic_halt(), ra8_board_clocks_init(), ra8_mstp_init(), and ra8_time_init().

Referenced by main().

◆ pdm_demo_emit_kv()

void pdm_demo_emit_kv	(	const uint8_t *	label,
		uint32_t	label_len,
		int32_t	value )

static

Emit "<label><value>" with a decimal integer.

Serializes the signed value into fixed stack storage after the label.

Parameters

[in]	label	Label bytes (non-NULL).
[in]	label_len	Label length.
[in]	value	Signed integer to print.

Returns: Nothing.

Precondition: The console was initialised.; label is non-NULL.

Postcondition: The label and value were queued for transmit.; No application state changed.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 303 of file main.c.

References k_pdm_demo_int_str_cap, pdm_demo_i32_to_dec(), and pdm_demo_tx().

Referenced by pdm_demo_publish().

◆ pdm_demo_i32_to_dec()

uint32_t pdm_demo_i32_to_dec	(	int32_t	value,
		uint8_t *	out )

static

Convert a signed 32-bit int into a decimal ASCII string.

Avoids newlib printf. Buffer must hold k_pdm_demo_int_str_cap.

Parameters

[in]	value	Integer to convert.
[out]	out	Destination buffer (>= 12 bytes, non-NULL).

Returns: Number of bytes written (excluding the NUL).

Return values

uint32_t Decimal character count excluding the terminator.

Precondition: out is non-NULL.; out has at least k_pdm_demo_int_str_cap bytes.

Postcondition: out holds a NUL-terminated decimal string.; The return value is in [1, 11].

Note: Pure helper; thread-safe.

Since: 0.1.0

Definition at line 196 of file main.c.

References k_pdm_demo_decimal, and k_pdm_demo_int_str_cap.

Referenced by pdm_demo_emit_kv().

◆ pdm_demo_io_or_halt()

void pdm_demo_io_or_halt ( void )

static

Route P812/P502 to the PDM function and open the console.

Both pins take PSEL k_ra8_psel_pdm; the console is SCI8.

Returns: Nothing.

Precondition: pdm_demo_clocks_or_halt already ran.; Single-threaded init context.

Postcondition: PDMCLK2/PDMDAT2 are routed and the console is live on success.; The CPU is parked on any failure.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 360 of file main.c.

References k_pdm_demo_baud, k_ra8_board_led1, k_ra8_ok, pdm_demo_panic_halt(), ra8_board_led_init(), ra8_board_pdm_mic_route(), and ra8_board_uart_console_init().

Referenced by main().

◆ pdm_demo_is_active()

bool pdm_demo_is_active ( const pdm_metrics_t * m )

static

Decide whether a window carries plausible live audio.

Non-degenerate (span >= k_pdm_demo_min_span) AND carrying AC energy (rms >= k_pdm_demo_rms_floor). Written as nested single-condition tests (no compound decision).

Parameters

[in] m Window metrics (non-NULL).

Returns: true if the window is plausible live audio.

Return values

true	The span and RMS meet their configured floors.
false	At least one activity threshold was not met.

Precondition: m was filled by pdm_demo_analyze.; m->n is greater than zero.

Postcondition: No state is modified.; The result reflects only m.

Note: Pure helper; thread-safe.

Since: 0.1.0

Definition at line 493 of file main.c.

References k_pdm_demo_min_span, k_pdm_demo_rms_floor, pdm_metrics_t::max, pdm_metrics_t::min, and pdm_metrics_t::rms.

Referenced by pdm_demo_run_window().

◆ pdm_demo_isqrt()

uint32_t pdm_demo_isqrt ( uint64_t value )

static

Integer square root of a 64-bit value (floor).

Bit-by-bit restoring algorithm; 32 fixed iterations, no FPU.

Parameters

[in] value Radicand.

Returns: floor(sqrt(value)).

Return values

uint32_t Greatest integer whose square does not exceed value.

Precondition: value is a mean-square accumulation.; No FPU dependency is required.

Postcondition: The result squared does not exceed value.; (result + 1) squared exceeds value.

Note: Pure helper; thread-safe.

Since: 0.1.0

Definition at line 244 of file main.c.

References k_pdm_isqrt_steps, and k_pdm_isqrt_top2.

Referenced by pdm_demo_analyze().

◆ pdm_demo_panic_halt()

void pdm_demo_panic_halt ( void )

static

Park forever after a fatal error.

Waits in a low-power spin; only a debugger or reset wakes it.

Returns: Never returns.

Precondition: Called only after a fatal init failure.; The console banner (if any) has been flushed.

Postcondition: The CPU is parked.; No further application code runs.

Note: Not callable from ISR context.

Since: 0.1.0

Definition at line 170 of file main.c.

Referenced by main(), pdm_demo_clocks_or_halt(), pdm_demo_io_or_halt(), and pdm_demo_pdm_or_halt().

◆ pdm_demo_pdm_or_halt()

void pdm_demo_pdm_or_halt ( void )

static

Bind the on-board MIC1 through the reusable PDM audio source.

Runs the HUM Ch 49.4.1 start flow with the settling delay. Prints k_pdm_demo_banner_fail and parks on any error.

Returns: Nothing.

Precondition: The console and clocks are live.; The PDM pins are routed.

Postcondition: Channel 2 is capturing on success.; The CPU is parked on any failure.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 387 of file main.c.

References ra8_board_pdm_mic_config_t::channel, k_pdm_demo_banner_fail, k_pdm_demo_banner_init, k_pdm_demo_discard, k_pdm_demo_poll_max, k_pdm_demo_settle_ms, k_pdm_demo_window, k_ra8_board_pdm_mic1, k_ra8_ok, ra8_board_pdm_mic_config_t::pdm, pdm_demo_panic_halt(), pdm_demo_tx(), ra8_audio_source_pdm_init(), ra8_board_pdm_mic_get_config(), s_pdm_demo_source, s_pdm_demo_source_state, ra8_board_pdm_mic_config_t::sample_rate_hz, and ra8_board_pdm_mic_config_t::valid_bits.

Referenced by main().

◆ pdm_demo_publish()

void pdm_demo_publish	(	const pdm_metrics_t *	m,
		int32_t	vary,
		bool	active )

static

Print a per-window detail line and latch g_pdm_mic_result.

Emits each metric as a bounded decimal field before updating the SWD result object.

Parameters

[in]	m	Window metrics (non-NULL).
[in]	vary	RMS spread across the report sweep so far.
[in]	active	Plausibility verdict for this window.

Returns: Nothing.

Precondition: The console is live.; m was filled by pdm_demo_analyze.

Postcondition: One pdm: ... detail line was emitted.; g_pdm_mic_result mirrors m.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 522 of file main.c.

References g_pdm_mic_result, k_pdm_demo_magic, pdm_metrics_t::max, pdm_metrics_t::mean, pdm_metrics_t::min, pdm_metrics_t::n, pdm_demo_emit_kv(), pdm_demo_tx(), pdm_metrics_t::peak, and pdm_metrics_t::rms.

Referenced by pdm_demo_run_window().

◆ pdm_demo_run_window()

bool pdm_demo_run_window	(	int32_t	vary,
		pdm_metrics_t *	out_m )

static

Capture one window, analyse it and publish it.

Reports the no-data banner and returns false if the FIFO never fills (dead clock / mic).

Parameters

[in]	vary	RMS spread so far (for the detail line).
[in,out]	out_m	Receives the window metrics (non-NULL).

Returns: true if a window was captured and analysed.

Return values

true	Capture, analysis, and publication completed.
false	The audio source did not provide a frame.

Precondition: The PDM channel is running with data read enabled.; out_m is non-NULL.

Postcondition: On success *out_m holds the window statistics.; g_pdm_mic_result is refreshed on success.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 577 of file main.c.

References g_pdm_mic_result, k_pdm_demo_banner_nodat, k_ra8_ok, pdm_demo_analyze(), pdm_demo_is_active(), pdm_demo_publish(), pdm_demo_tx(), ra8_audio_source_capture(), s_pdm_demo_buf, s_pdm_demo_source, ra8_audio_frame_t::sample_count, and ra8_audio_frame_t::timestamp_ms.

Referenced by main().

◆ pdm_demo_tx()

void pdm_demo_tx	(	const uint8_t *	bytes,
		uint32_t	len )

static

Emit a byte run over the SCI8 console.

Forwards the exact caller span through the board console without formatting.

Parameters

[in]	bytes	Byte array (non-NULL).
[in]	len	Byte count.

Returns: Nothing.

Precondition: The console was initialised.; bytes is non-NULL.

Postcondition: len bytes were queued for transmit.; No application state changed.

Note: Not thread-safe.

Since: 0.1.0

Definition at line 280 of file main.c.

References ra8_board_uart_console_write().

Referenced by main(), pdm_demo_emit_kv(), pdm_demo_pdm_or_halt(), pdm_demo_publish(), and pdm_demo_run_window().

Variable Documentation

◆ g_pdm_mic_result

volatile pdm_mic_result_t g_pdm_mic_result

J-Link-probable capture result (read at &g_pdm_mic_result).

Definition at line 123 of file main.c.

Referenced by main(), pdm_demo_publish(), and pdm_demo_run_window().

◆ k_pdm_demo_banner_fail

const uint8_t k_pdm_demo_banner_fail[] = "pdm: init FAIL\r\n"

static

Definition at line 145 of file main.c.

Referenced by pdm_demo_pdm_or_halt().

◆ k_pdm_demo_banner_inactive

const uint8_t k_pdm_demo_banner_inactive[] = "pdm: verdict=FAIL active=N\r\n"

static

Definition at line 148 of file main.c.

Referenced by main().

◆ k_pdm_demo_banner_init

const uint8_t k_pdm_demo_banner_init[] = "pdm: init ch=2 clk=4mhz fs=16khz\r\n"

static

Definition at line 144 of file main.c.

Referenced by pdm_demo_pdm_or_halt().

◆ k_pdm_demo_banner_nodat

const uint8_t k_pdm_demo_banner_nodat[] = "pdm: no data (FIFO empty) -- clock/mic?\r\n"

static

Definition at line 146 of file main.c.

Referenced by pdm_demo_run_window().

◆ k_pdm_demo_banner_pass

const uint8_t k_pdm_demo_banner_pass[] = "pdm: verdict=PASS active=Y\r\n"

static

Definition at line 147 of file main.c.

Referenced by main().

◆ s_pdm_demo_buf

int32_t s_pdm_demo_buf[k_pdm_demo_window]

static

Static capture buffer (kept off the stack).

Definition at line 126 of file main.c.

Referenced by pdm_demo_run_window().

◆ s_pdm_demo_source

ra8_audio_source_t s_pdm_demo_source

static

Generic caller-owned audio source handle.

Definition at line 129 of file main.c.

Referenced by pdm_demo_pdm_or_halt(), and pdm_demo_run_window().

◆ s_pdm_demo_source_state

ra8_audio_source_pdm_state_t s_pdm_demo_source_state

static

Caller-owned PDM backend state.

Definition at line 132 of file main.c.

Referenced by pdm_demo_pdm_or_halt().

Data Structures

Enumerations

Functions

Variables

Detailed Description

Enumeration Type Documentation

◆ pdm_demo_const_t

◆ pdm_demo_magic_t

◆ pdm_demo_str_cap_t

◆ pdm_demo_threshold_t

◆ pdm_isqrt_const_t

Function Documentation

◆ main()

◆ pdm_demo_analyze()

◆ pdm_demo_clocks_or_halt()

◆ pdm_demo_emit_kv()

◆ pdm_demo_i32_to_dec()

◆ pdm_demo_io_or_halt()

◆ pdm_demo_is_active()

◆ pdm_demo_isqrt()

◆ pdm_demo_panic_halt()

◆ pdm_demo_pdm_or_halt()

◆ pdm_demo_publish()

◆ pdm_demo_run_window()

◆ pdm_demo_tx()

Variable Documentation

◆ g_pdm_mic_result

◆ k_pdm_demo_banner_fail

◆ k_pdm_demo_banner_inactive

◆ k_pdm_demo_banner_init

◆ k_pdm_demo_banner_nodat

◆ k_pdm_demo_banner_pass

◆ s_pdm_demo_buf

◆ s_pdm_demo_source

◆ s_pdm_demo_source_state