Interrupt-driven onboard PDM microphone recorder for camera servers. More...

#include <stdint.h>
#include <string.h>
#include "c6_camera_server.h"
#include "ra8_attributes.h"
#include "ra8_audio.h"
#include "ra8_audio_source_pdm.h"
#include "ra8_board_ek_ra8d2.h"
#include "ra8_err.h"
#include "ra8_register_guard.h"

Include dependency graph for c6_cam_audio.c:

Data Structures
struct	c6_cam_audio_bank_t
	Writer position and timing metadata for one SDRAM audio bank. More...

Enumerations
enum	c6_cam_audio_cfg_t : uint32_t { k_c6_cam_audio_rate_hz = 16000U , k_c6_cam_audio_frame_samples = 256U , k_c6_cam_audio_ring_samples = 16000U , k_c6_cam_audio_settle_ms = 300U , k_c6_cam_audio_discard = 1024U , k_c6_cam_audio_poll_attempts = 500000U , k_c6_cam_audio_irq_priority = 5U , k_c6_cam_audio_bank_count = 2U , k_c6_cam_audio_gain = 16U , k_c6_cam_wav_header_bytes = 44U , k_c6_cam_wav_sample_bytes = 2U , k_c6_cam_wav_capacity , k_c6_cam_byte_mask = 0xFFU , k_c6_cam_shift_24 = 24U , k_c6_cam_ms_per_second = 1000U , k_c6_cam_wav_riff_overhead = 36U , k_c6_cam_wav_audio_format_off = 20U , k_c6_cam_wav_channels_off = 22U , k_c6_cam_wav_byte_rate_off = 28U , k_c6_cam_wav_bits_off = 34U , k_c6_cam_wav_data_size_off = 40U }
	Audio capture, storage, and WAV constants. More...

Functions
static void	internal_c6_cam_audio_put_u16 (uint8_t *out, uint16_t value)
	Write one little-endian 16-bit scalar.
static void	internal_c6_cam_audio_put_u32 (uint8_t *out, uint32_t value)
	Write one little-endian 32-bit scalar.
static int16_t	internal_c6_cam_audio_s16 (int32_t sample)
	Convert signed 20-bit PDM PCM to saturated signed 16-bit PCM.
static void	internal_c6_cam_audio_on_frame (void ctx, const ra8_audio_frame_t frame)
	Append one complete audio frame to the active SDRAM ring.
static void	internal_c6_cam_audio_write_header (uint32_t samples)
	Serialize the canonical mono PCM-S16LE WAV header.
ra8_err_t	c6_cam_audio_start (void)
	Start continuous MIC1 capture into the SDRAM audio ring.
ra8_err_t	c6_cam_audio_snapshot_wav (const uint8_t *out_wav, uint32_t out_bytes, uint32_t *out_timestamp_ms)
	Snapshot the rolling microphone ring as mono PCM-S16LE WAV.

Variables
static ra8_audio_source_t	s_audio_source
	Fixed audio source objects and interrupt assembly scratch.
static ra8_audio_source_pdm_state_t	s_audio_state
static int32_t	s_audio_frame [k_c6_cam_audio_frame_samples]
static int32_t	s_audio_ring [k_c6_cam_audio_bank_count][k_c6_cam_audio_ring_samples]
	Ping-pong PCM rings and generated WAV live in external SDRAM.
static uint8_t	s_audio_wav [k_c6_cam_wav_capacity]
static volatile uint8_t	s_audio_active_bank
	Active ISR bank and per-bank metadata guarded during handoff.
static c6_cam_audio_bank_t	s_audio_banks [k_c6_cam_audio_bank_count]
static const uint8_t	s_wav_tag_riff [] = {'R', 'I', 'F', 'F'}
	The three fixed-width chunk tags of a canonical PCM WAV header.
static const uint8_t	s_wav_tag_wavefmt [] = {'W', 'A', 'V', 'E', 'f', 'm', 't', ' '}
static const uint8_t	s_wav_tag_data [] = {'d', 'a', 't', 'a'}

Detailed Description

Interrupt-driven onboard PDM microphone recorder for camera servers.

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

The PDM-IF hardware continuously decimates MIC1 into 20-bit PCM. The generic ra8_audio PDM backend assembles fixed frames in interrupt context, then this module appends them to a caller-owned one-second SDRAM bank. HTTP requests atomically hand capture to the other SDRAM bank and expose the stable bank as PCM-S16LE WAV without stopping the PDM source, camera capture, or allocating memory.

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

Since: 0.1.0

Definition in file c6_cam_audio.c.

Enumeration Type Documentation

◆ c6_cam_audio_cfg_t

enum c6_cam_audio_cfg_t : uint32_t

Audio capture, storage, and WAV constants.

Enumerator
k_c6_cam_audio_rate_hz	Mono PCM sample rate.
k_c6_cam_audio_frame_samples	Samples assembled per IRQ frame.
k_c6_cam_audio_ring_samples	One-second rolling sample window.
k_c6_cam_audio_settle_ms	Microphone/filter settling delay.
k_c6_cam_audio_discard	Startup transient samples.
k_c6_cam_audio_poll_attempts	Initialization polling bound.
k_c6_cam_audio_irq_priority	PDM FIFO NVIC priority.
k_c6_cam_audio_bank_count	Ping-pong SDRAM capture banks.
k_c6_cam_audio_gain	WAV digital gain before scaling.
k_c6_cam_wav_header_bytes	Canonical PCM WAV header size.
k_c6_cam_wav_sample_bytes	PCM-S16LE bytes per mono sample.
k_c6_cam_wav_capacity	Complete WAV capacity.
k_c6_cam_byte_mask	One serialized byte mask.
k_c6_cam_shift_24	Most-significant byte shift.
k_c6_cam_ms_per_second	Milliseconds per second.
k_c6_cam_wav_riff_overhead	RIFF size excluding 8-byte lead.
k_c6_cam_wav_audio_format_off	WAV audio-format field offset.
k_c6_cam_wav_channels_off	WAV channel-count field offset.
k_c6_cam_wav_byte_rate_off	WAV byte-rate field offset.
k_c6_cam_wav_bits_off	WAV bits-per-sample field offset.
k_c6_cam_wav_data_size_off	WAV data-size field offset.

Definition at line 32 of file c6_cam_audio.c.

Function Documentation

◆ c6_cam_audio_snapshot_wav()

ra8_err_t c6_cam_audio_snapshot_wav	(	const uint8_t **	out_wav,
		uint32_t *	out_bytes,
		uint32_t *	out_timestamp_ms )

nodiscard

Snapshot the rolling microphone ring as mono PCM-S16LE WAV.

Definition at line 273 of file c6_cam_audio.c.

References internal_c6_cam_audio_put_u16(), internal_c6_cam_audio_s16(), internal_c6_cam_audio_write_header(), k_c6_cam_audio_ring_samples, k_c6_cam_wav_header_bytes, k_c6_cam_wav_sample_bytes, k_ra8_err_no_data, k_ra8_err_null_ptr, k_ra8_ok, ra8_register_guard_enter(), ra8_register_guard_exit(), s_audio_active_bank, s_audio_banks, s_audio_ring, and s_audio_wav.

Referenced by internal_c6_cam_http_audio().

◆ c6_cam_audio_start()

ra8_err_t c6_cam_audio_start ( void )

nodiscard

Start continuous MIC1 capture into the SDRAM audio ring.

Definition at line 229 of file c6_cam_audio.c.

References ra8_board_pdm_mic_config_t::channel, internal_c6_cam_audio_on_frame(), k_c6_cam_audio_discard, k_c6_cam_audio_frame_samples, k_c6_cam_audio_irq_priority, k_c6_cam_audio_poll_attempts, k_c6_cam_audio_rate_hz, k_c6_cam_audio_settle_ms, k_ra8_board_pdm_mic1, k_ra8_err_invalid_state, k_ra8_ok, ra8_board_pdm_mic_config_t::pdm, ra8_audio_source_pdm_init(), ra8_audio_source_stop(), ra8_audio_source_stream_start(), ra8_board_pdm_mic_get_config(), ra8_board_pdm_mic_route(), s_audio_frame, s_audio_source, s_audio_state, ra8_board_pdm_mic_config_t::sample_rate_hz, and ra8_board_pdm_mic_config_t::valid_bits.

Referenced by internal_c6_cam_prepare_media().

◆ internal_c6_cam_audio_on_frame()

void internal_c6_cam_audio_on_frame	(	void *	ctx,
		const ra8_audio_frame_t *	frame )

static

Append one complete audio frame to the active SDRAM ring.

Writes interrupt-delivered PCM into the selected bank and updates bounded metadata.

Parameters

[in,out]	ctx	Unused callback context.
[in]	frame	Borrowed PCM-S32LE audio frame.

Precondition: frame is null or remains valid for the callback duration.; The active bank index selects one of the two static banks.

Postcondition: Valid samples are appended with circular wraparound.; Metadata describes retained count, next write index, and oldest timestamp.

Note: This callback runs in the PDM interrupt path.

Since: 0.1.0

Definition at line 170 of file c6_cam_audio.c.

References ra8_audio_frame_t::data, ra8_audio_frame_t::format, k_c6_cam_audio_rate_hz, k_c6_cam_audio_ring_samples, k_c6_cam_ms_per_second, k_ra8_audio_format_pcm_s32le, c6_cam_audio_bank_t::oldest_timestamp_ms, RA8_INTERNAL, s_audio_active_bank, s_audio_banks, s_audio_ring, c6_cam_audio_bank_t::sample_count, ra8_audio_frame_t::sample_count, ra8_audio_frame_t::timestamp_ms, and c6_cam_audio_bank_t::write_index.

Referenced by c6_cam_audio_start().

◆ internal_c6_cam_audio_put_u16()

void internal_c6_cam_audio_put_u16	(	uint8_t *	out,
		uint16_t	value )

static

Write one little-endian 16-bit scalar.

Splits the value into two wire-order WAV bytes.

Parameters

[out]	out	Destination for two bytes.
[in]	value	Scalar to serialize.

Precondition: out addresses at least two writable bytes.; No concurrent writer modifies the same destination bytes.

Postcondition: out[0] contains the least-significant byte.; out[1] contains the most-significant byte.

Note: The helper performs no alignment-dependent stores.

Since: 0.1.0

Definition at line 105 of file c6_cam_audio.c.

References k_c6_cam_byte_mask, and RA8_INTERNAL.

Referenced by c6_cam_audio_snapshot_wav(), and internal_c6_cam_audio_write_header().

◆ internal_c6_cam_audio_put_u32()

void internal_c6_cam_audio_put_u32	(	uint8_t *	out,
		uint32_t	value )

static

Write one little-endian 32-bit scalar.

Splits the value into four wire-order WAV bytes.

Parameters

[out]	out	Destination for four bytes.
[in]	value	Scalar to serialize.

Precondition: out addresses at least four writable bytes.; No concurrent writer modifies the same destination bytes.

Postcondition: Destination bytes contain value in little-endian order.; No byte beyond the four-byte destination span is modified.

Note: The helper performs no alignment-dependent stores.

Since: 0.1.0

Definition at line 123 of file c6_cam_audio.c.

References k_c6_cam_byte_mask, k_c6_cam_shift_24, and RA8_INTERNAL.

Referenced by internal_c6_cam_audio_write_header().

◆ internal_c6_cam_audio_s16()

int16_t internal_c6_cam_audio_s16 ( int32_t sample )

static

Convert signed 20-bit PDM PCM to saturated signed 16-bit PCM.

Applies fixed application gain, removes four low-significance bits, then saturates to the WAV range.

Parameters

[in] sample Signed sample supplied by the PDM backend.

Returns: Converted PCM sample.

Return values

INT16_MAX	The scaled input exceeded positive 16-bit range.
INT16_MIN	The scaled input exceeded negative 16-bit range.

Precondition: sample is a sign-extended PDM sample or another valid signed integer.; No mutable audio state is required.

Postcondition: The result lies in the signed 16-bit range.; Global ring and WAV storage remain unchanged.

Note: Integer division intentionally discards four low bits.

Since: 0.1.0

Definition at line 146 of file c6_cam_audio.c.

References k_c6_cam_audio_gain, and RA8_INTERNAL.

Referenced by c6_cam_audio_snapshot_wav().

◆ internal_c6_cam_audio_write_header()

void internal_c6_cam_audio_write_header ( uint32_t samples )

static

Serialize the canonical mono PCM-S16LE WAV header.

Writes RIFF, format, rate, alignment, and data-size fields into static storage.

Parameters

[in] samples Number of mono samples following the header.

Precondition: samples does not exceed the configured ring capacity.; s_audio_wav is not concurrently served while the snapshot is built.

Postcondition: The first 44 bytes contain a self-consistent PCM-S16LE WAV header.; Payload bytes after the header remain unchanged.

Note: The sample rate is fixed at 16 kHz mono.

Since: 0.1.0

Definition at line 210 of file c6_cam_audio.c.

References internal_c6_cam_audio_put_u16(), internal_c6_cam_audio_put_u32(), k_c6_cam_audio_rate_hz, k_c6_cam_wav_audio_format_off, k_c6_cam_wav_bits_off, k_c6_cam_wav_byte_rate_off, k_c6_cam_wav_channels_off, k_c6_cam_wav_data_size_off, k_c6_cam_wav_riff_overhead, k_c6_cam_wav_sample_bytes, memcpy(), RA8_INTERNAL, s_audio_wav, s_wav_tag_data, s_wav_tag_riff, and s_wav_tag_wavefmt.

Referenced by c6_cam_audio_snapshot_wav().

Variable Documentation

◆ s_audio_active_bank

volatile uint8_t s_audio_active_bank

static

Active ISR bank and per-bank metadata guarded during handoff.

Definition at line 77 of file c6_cam_audio.c.

Referenced by c6_cam_audio_snapshot_wav(), and internal_c6_cam_audio_on_frame().

◆ s_audio_banks

c6_cam_audio_bank_t s_audio_banks[k_c6_cam_audio_bank_count]

static

Definition at line 78 of file c6_cam_audio.c.

Referenced by c6_cam_audio_snapshot_wav(), and internal_c6_cam_audio_on_frame().

◆ s_audio_frame

int32_t s_audio_frame[k_c6_cam_audio_frame_samples]

static

Definition at line 68 of file c6_cam_audio.c.

Referenced by c6_cam_audio_start().

◆ s_audio_ring

int32_t s_audio_ring[k_c6_cam_audio_bank_count][k_c6_cam_audio_ring_samples]

static

Ping-pong PCM rings and generated WAV live in external SDRAM.

Definition at line 73 of file c6_cam_audio.c.

Referenced by c6_cam_audio_snapshot_wav(), and internal_c6_cam_audio_on_frame().

◆ s_audio_source

ra8_audio_source_t s_audio_source

static

Fixed audio source objects and interrupt assembly scratch.

Definition at line 66 of file c6_cam_audio.c.

Referenced by c6_cam_audio_start().

◆ s_audio_state

ra8_audio_source_pdm_state_t s_audio_state

static

Definition at line 67 of file c6_cam_audio.c.

Referenced by c6_cam_audio_start().

◆ s_audio_wav

uint8_t s_audio_wav[k_c6_cam_wav_capacity]

static

Definition at line 74 of file c6_cam_audio.c.

Referenced by c6_cam_audio_snapshot_wav(), and internal_c6_cam_audio_write_header().

◆ s_wav_tag_data

const uint8_t s_wav_tag_data[] = {'d', 'a', 't', 'a'}

static

Definition at line 91 of file c6_cam_audio.c.

Referenced by internal_c6_cam_audio_write_header().

◆ s_wav_tag_riff

const uint8_t s_wav_tag_riff[] = {'R', 'I', 'F', 'F'}

static

The three fixed-width chunk tags of a canonical PCM WAV header.

Byte arrays rather than C strings, because that is what the file format is: each tag is followed immediately by a binary length or format field, so the header carries no terminator after any of them and copying one would corrupt the field that follows.

Note: Read-only; only internal_c6_cam_audio_write_header copies them.

Since: 0.1.0

Definition at line 89 of file c6_cam_audio.c.

Referenced by internal_c6_cam_audio_write_header().

◆ s_wav_tag_wavefmt

const uint8_t s_wav_tag_wavefmt[] = {'W', 'A', 'V', 'E', 'f', 'm', 't', ' '}

static

Definition at line 90 of file c6_cam_audio.c.

Referenced by internal_c6_cam_audio_write_header().

Data Structures

Enumerations

Functions

Variables

Detailed Description

Enumeration Type Documentation

◆ c6_cam_audio_cfg_t

Function Documentation

◆ c6_cam_audio_snapshot_wav()

◆ c6_cam_audio_start()

◆ internal_c6_cam_audio_on_frame()

◆ internal_c6_cam_audio_put_u16()

◆ internal_c6_cam_audio_put_u32()

◆ internal_c6_cam_audio_s16()

◆ internal_c6_cam_audio_write_header()

Variable Documentation

◆ s_audio_active_bank

◆ s_audio_banks

◆ s_audio_frame

◆ s_audio_ring

◆ s_audio_source

◆ s_audio_state

◆ s_audio_wav

◆ s_wav_tag_data

◆ s_wav_tag_riff

◆ s_wav_tag_wavefmt