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Improve PDM microphone reliability #33

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merged 3 commits into from
Dec 17, 2019
Merged

Improve PDM microphone reliability #33

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055af04
PDM: use HFCLK clock
facchinm Nov 26, 2019
6fb51dd
PDM: respect microphone min_freq specifications
facchinm Nov 26, 2019
545c4c5
PDM: only enable HFCLK if needed
facchinm Nov 29, 2019
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11 changes: 10 additions & 1 deletion libraries/PDM/src/PDM.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -48,10 +48,17 @@ int PDMClass::begin(int channels, long sampleRate)
{
_channels = channels;

// Enable high frequency oscillator if not already enabled
if (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) {
NRF_CLOCK->TASKS_HFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) { }
}

// configure the sample rate and channels
switch (sampleRate) {
case 16000:
nrf_pdm_clock_set(NRF_PDM_FREQ_1032K);
NRF_PDM->RATIO = ((PDM_RATIO_RATIO_Ratio80 << PDM_RATIO_RATIO_Pos) & PDM_RATIO_RATIO_Msk);
nrf_pdm_clock_set(NRF_PDM_FREQ_1280K);
break;
case 41667:
nrf_pdm_clock_set(NRF_PDM_FREQ_2667K);
Expand Down Expand Up @@ -128,6 +135,8 @@ void PDMClass::end()
pinMode(_pwrPin, INPUT);
}

// Don't disable high frequency oscillator since it could be in use by RADIO

// unconfigure the I/O and un-mux
nrf_pdm_psel_disconnect();

Expand Down