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drivers: clock_control: nrf2: improve audiopll clock calculations #97735

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drivers: clock_control: nrf2: improve audiopll clock calculations #97735

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49 changes: 29 additions & 20 deletions drivers/clock_control/clock_control_nrfs_audiopll.c
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@
#include <zephyr/logging/log.h>
LOG_MODULE_DECLARE(clock_control_nrf2, CONFIG_CLOCK_CONTROL_LOG_LEVEL);

#define SHIM_DEFAULT_PRESCALER AUDIOPLL_DIV_12
#define SHIM_DEFAULT_PRESCALER 12

BUILD_ASSERT(
DT_NUM_INST_STATUS_OKAY(DT_DRV_COMPAT) == 1,
Expand All @@ -33,6 +33,25 @@ struct shim_data {
nrfs_audiopll_evt_type_t evt;
};

static enum audiopll_prescaler_div get_prescaler_div(uint8_t divider)
{
switch (divider) {
case 0:
return AUDIOPLL_DIV_DISABLED;
case 6:
return AUDIOPLL_DIV_6;
case 8:
return AUDIOPLL_DIV_8;
case 12:
return AUDIOPLL_DIV_12;
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@bjarki-andreasen bjarki-andreasen Oct 17, 2025 •
edited
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Prescaler div 12 was the only used and valid prescaler when this driver was written, has that changed?

case 16:
return AUDIOPLL_DIV_16;
default:
__ASSERT(divider <= 4, "invalid audiopll divider");
return (enum audiopll_prescaler_div)divider;
}
Comment on lines +38 to +52
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The values seem to originate from nrfs header, but I have no idea why nrfs makes them available. I would prefer if AudioPLL just continues to use hardcoded AUDIOPLL_DIV_12 which is known to work.

}

static int shim_nrfs_request_enable(const struct device *dev)
{
struct shim_data *dev_data = dev->data;
Expand Down Expand Up @@ -103,30 +122,19 @@ static const struct onoff_transitions shim_mgr_transitions = {
/*
* Formula:
*
* frequency = ((4 + (freq_fraction * 2^-16)) * 32000000) / 12
*
* Simplified linear approximation:
*
* frequency = 10666666 + (((13333292 - 10666666) / 65535) * freq_fraction)
* frequency = 10666666 + ((2666626 / 65535) * freq_fraction)
* frequency = ((10666666 * 65535) + (2666626 * freq_fraction)) / 65535
* frequency = (699039956310 + (2666626 * freq_fraction)) / 65535
* frequency = ((4 + (freq_fraction * 2^-16)) * 32000000) / PRESCALER_DIV
*
* Isolate freq_fraction:
* Solving for freq_fraction:
*
* frequency = (699039956310 + (2666626 * freq_fraction)) / 65535
* frequency * 65535 = 699039956310 + (2666626 * freq_fraction)
* (frequency * 65535) - 699039956310 = 2666626 * freq_fraction
* freq_fraction = ((frequency * 65535) - 699039956310) / 2666626
* freq_fraction = (32 * PRESCALER_DIV * frequency) / 15625 - 262144
*/
static uint16_t shim_frequency_to_freq_fraction(uint32_t frequency)
static uint16_t shim_frequency_to_freq_fraction(uint32_t frequency, uint8_t prescaler_div)
{
uint64_t freq_fraction;

freq_fraction = frequency;
freq_fraction *= 65535;
freq_fraction -= 699039956310;
freq_fraction = DIV_ROUND_CLOSEST(freq_fraction, 2666626);
freq_fraction *= 32 * prescaler_div;
freq_fraction = DIV_ROUND_CLOSEST(freq_fraction, 15625) - 262144;

return (uint16_t)freq_fraction;
}
Expand Down Expand Up @@ -256,13 +264,14 @@ static int shim_init(const struct device *dev)
return -ENODEV;
}

ret = shim_nrfs_request_prescaler_sync(dev, SHIM_DEFAULT_PRESCALER);
ret = shim_nrfs_request_prescaler_sync(dev, get_prescaler_div(SHIM_DEFAULT_PRESCALER));
if (ret) {
LOG_ERR("failed to set prescaler divider");
return ret;
}

freq_fraction = shim_frequency_to_freq_fraction(DT_INST_PROP(0, frequency));
freq_fraction =
shim_frequency_to_freq_fraction(DT_INST_PROP(0, frequency), SHIM_DEFAULT_PRESCALER);

LOG_DBG("requesting freq_fraction %u for frequency %uHz",
freq_fraction,
Expand Down