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[nrf fromlist] drivers: audio: dmic_nrfx_pdm: introduce prescaler cal… #3319

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Oct 14, 2025
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[nrf fromlist] drivers: audio: dmic_nrfx_pdm: introduce prescaler cal… #3319

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227 changes: 10 additions & 217 deletions drivers/audio/dmic_nrfx_pdm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,6 @@

#if CONFIG_SOC_SERIES_NRF54HX
#define DMIC_NRFX_CLOCK_FREQ MHZ(16)
#define DMIC_NRFX_CLOCK_FACTOR 8192
#define DMIC_NRFX_AUDIO_CLOCK_FREQ DT_PROP_OR(NODE_AUDIOPLL, frequency, 0)
#elif DT_NODE_HAS_STATUS_OKAY(NODE_AUDIO_AUXPLL)
#define DMIC_NRFX_AUDIO_CLOCK_FREQ DT_PROP(NODE_AUDIO_AUXPLL, nordic_frequency)
Expand All @@ -31,7 +30,6 @@
#define DMIC_NRFX_CLOCK_FREQ MHZ(32)
#else
#define DMIC_NRFX_CLOCK_FREQ MHZ(32)
#define DMIC_NRFX_CLOCK_FACTOR 4096
#define DMIC_NRFX_AUDIO_CLOCK_FREQ DT_PROP_OR(DT_NODELABEL(aclk), clock_frequency, \
DT_PROP_OR(DT_NODELABEL(clock), hfclkaudio_frequency, 0))
#endif
Expand Down Expand Up @@ -202,220 +200,6 @@
}
}

static bool is_in_freq_range(uint32_t freq, const struct dmic_cfg *pdm_cfg)
{
return freq >= pdm_cfg->io.min_pdm_clk_freq && freq <= pdm_cfg->io.max_pdm_clk_freq;
}

static bool is_better(uint32_t freq,
uint8_t ratio,
uint32_t req_rate,
uint32_t *best_diff,
uint32_t *best_rate,
uint32_t *best_freq)
{
uint32_t act_rate = freq / ratio;
uint32_t diff = act_rate >= req_rate ? (act_rate - req_rate)
: (req_rate - act_rate);

LOG_DBG("Freq %u, ratio %u, act_rate %u", freq, ratio, act_rate);

if (diff < *best_diff) {
*best_diff = diff;
*best_rate = act_rate;
*best_freq = freq;
return true;
}

return false;
}

static bool check_pdm_frequencies(const struct dmic_nrfx_pdm_drv_cfg *drv_cfg,
nrfx_pdm_config_t *config,
const struct dmic_cfg *pdm_cfg,
uint8_t ratio,
uint32_t *best_diff,
uint32_t *best_rate,
uint32_t *best_freq)
{
uint32_t req_rate = pdm_cfg->streams[0].pcm_rate;
bool better_found = false;
const uint32_t src_freq =
(NRF_PDM_HAS_SELECTABLE_CLOCK && drv_cfg->clk_src == ACLK)
? DMIC_NRFX_AUDIO_CLOCK_FREQ
: DMIC_NRFX_CLOCK_FREQ;
#if NRF_PDM_HAS_PRESCALER
uint32_t req_freq = req_rate * ratio;
uint32_t prescaler = src_freq / req_freq;
uint32_t act_freq = src_freq / prescaler;

if (is_in_freq_range(act_freq, pdm_cfg) &&
is_better(act_freq, ratio, req_rate, best_diff, best_rate, best_freq)) {
config->prescaler = prescaler;

better_found = true;
}

/* Stop if an exact rate match is found. */
if (*best_diff == 0) {
return true;
}

/* Prescaler value is rounded down by default,
* thus value rounded up should be checked as well.
*/
prescaler += 1;
act_freq = src_freq / prescaler;

if (is_in_freq_range(act_freq, pdm_cfg) &&
is_better(act_freq, ratio, req_rate, best_diff, best_rate, best_freq)) {
config->prescaler = prescaler;

better_found = true;
}
#else
if (IS_ENABLED(CONFIG_SOC_SERIES_NRF53X) || IS_ENABLED(CONFIG_SOC_SERIES_NRF54HX)) {
uint32_t req_freq = req_rate * ratio;
/* As specified in the nRF5340 PS:
*
* PDMCLKCTRL = 4096 * floor(f_pdm * 1048576 /
* (f_source + f_pdm / 2))
* f_actual = f_source / floor(1048576 * 4096 / PDMCLKCTRL)
*/
uint32_t clk_factor = (uint32_t)((req_freq * 1048576ULL) /
(src_freq + req_freq / 2));
uint32_t act_freq = src_freq / (1048576 / clk_factor);

if (is_in_freq_range(act_freq, pdm_cfg) &&
is_better(act_freq, ratio, req_rate, best_diff, best_rate, best_freq)) {
config->clock_freq = clk_factor * DMIC_NRFX_CLOCK_FACTOR;

better_found = true;
}
} else { /* -> !IS_ENABLED(CONFIG_SOC_SERIES_NRF53X)) */
static const struct {
uint32_t freq_val;
nrf_pdm_freq_t freq_enum;
} freqs[] = {
{ 1000000, NRF_PDM_FREQ_1000K },
{ 1032000, NRF_PDM_FREQ_1032K },
{ 1067000, NRF_PDM_FREQ_1067K },
#if defined(PDM_PDMCLKCTRL_FREQ_1231K)
{ 1231000, NRF_PDM_FREQ_1231K },
#endif
#if defined(PDM_PDMCLKCTRL_FREQ_1280K)
{ 1280000, NRF_PDM_FREQ_1280K },
#endif
#if defined(PDM_PDMCLKCTRL_FREQ_1333K)
{ 1333000, NRF_PDM_FREQ_1333K }
#endif
};

for (int i = 0; i < ARRAY_SIZE(freqs); ++i) {
uint32_t freq_val = freqs[i].freq_val;

if (freq_val < pdm_cfg->io.min_pdm_clk_freq) {
continue;
}
if (freq_val > pdm_cfg->io.max_pdm_clk_freq) {
break;
}

if (is_better(freq_val, ratio, req_rate,
best_diff, best_rate, best_freq)) {
config->clock_freq = freqs[i].freq_enum;

/* Stop if an exact rate match is found. */
if (*best_diff == 0) {
return true;
}

better_found = true;
}

/* Since frequencies are in ascending order, stop
* checking next ones for the current ratio after
* resulting PCM rate goes above the one requested.
*/
if ((freq_val / ratio) > req_rate) {
break;
}
}
}
#endif /* NRF_PDM_HAS_PRESCALER */

return better_found;
}

/* Finds clock settings that give the PCM output rate closest to that requested,
* taking into account the hardware limitations.
*/
static bool find_suitable_clock(const struct dmic_nrfx_pdm_drv_cfg *drv_cfg,
nrfx_pdm_config_t *config,
const struct dmic_cfg *pdm_cfg)
{
uint32_t best_diff = UINT32_MAX;
uint32_t best_rate;
uint32_t best_freq;

#if NRF_PDM_HAS_RATIO_CONFIG
static const struct {
uint8_t ratio_val;
nrf_pdm_ratio_t ratio_enum;
} ratios[] = {
#if defined(PDM_RATIO_RATIO_Ratio32)
{ 32, NRF_PDM_RATIO_32X },
#endif
#if defined(PDM_RATIO_RATIO_Ratio48)
{ 48, NRF_PDM_RATIO_48X },
#endif
#if defined(PDM_RATIO_RATIO_Ratio50)
{ 50, NRF_PDM_RATIO_50X },
#endif
{ 64, NRF_PDM_RATIO_64X },
{ 80, NRF_PDM_RATIO_80X },
#if defined(PDM_RATIO_RATIO_Ratio96)
{ 96, NRF_PDM_RATIO_96X },
#endif
#if defined(PDM_RATIO_RATIO_Ratio100)
{ 100, NRF_PDM_RATIO_100X },
#endif
#if defined(PDM_RATIO_RATIO_Ratio128)
{ 128, NRF_PDM_RATIO_128X }
#endif
};

for (int r = 0; best_diff != 0 && r < ARRAY_SIZE(ratios); ++r) {
uint8_t ratio = ratios[r].ratio_val;

if (check_pdm_frequencies(drv_cfg, config, pdm_cfg, ratio,
&best_diff, &best_rate, &best_freq)) {
config->ratio = ratios[r].ratio_enum;

/* Look no further if a configuration giving the exact
* PCM rate is found.
*/
if (best_diff == 0) {
break;
}
}
}
#else
uint8_t ratio = 64;

(void)check_pdm_frequencies(drv_cfg, config, pdm_cfg, ratio,
&best_diff, &best_rate, &best_freq);
#endif

if (best_diff == UINT32_MAX) {
return false;
}

LOG_INF("PDM clock frequency: %u, actual PCM rate: %u",
best_freq, best_rate);
return true;
}

static int dmic_nrfx_pdm_configure(const struct device *dev,
struct dmic_cfg *config)
{
Expand Down Expand Up @@ -499,7 +283,16 @@
? NRF_PDM_MCLKSRC_ACLK
: NRF_PDM_MCLKSRC_PCLK32M;
#endif
if (!find_suitable_clock(drv_cfg, &nrfx_cfg, config)) {
nrfx_pdm_output_t output_config = {
.base_clock_freq = (NRF_PDM_HAS_SELECTABLE_CLOCK && drv_cfg->clk_src == ACLK)
? DMIC_NRFX_AUDIO_CLOCK_FREQ
: DMIC_NRFX_CLOCK_FREQ,
.sampling_rate = config->streams[0].pcm_rate,
.output_freq_min = config->io.min_pdm_clk_freq,
.output_freq_max = config->io.max_pdm_clk_freq
};

Check notice on line 294 in drivers/audio/dmic_nrfx_pdm.c

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drivers/audio/dmic_nrfx_pdm.c:294 
-					? DMIC_NRFX_AUDIO_CLOCK_FREQ
-					: DMIC_NRFX_CLOCK_FREQ,
+					   ? DMIC_NRFX_AUDIO_CLOCK_FREQ
+					   : DMIC_NRFX_CLOCK_FREQ,
 		.sampling_rate = config->streams[0].pcm_rate,
 		.output_freq_min = config->io.min_pdm_clk_freq,
-		.output_freq_max = config->io.max_pdm_clk_freq
-	};
+		.output_freq_max = config->io.max_pdm_clk_freq};
if (nrfx_pdm_prescalers_calc(&output_config, &nrfx_cfg.prescalers) != NRFX_SUCCESS) {
LOG_ERR("Cannot find suitable PDM clock configuration.");
return -EINVAL;
}
Expand Down
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