Posted on March 11, 2018 at 16:38Hi,
I have get pdm data and want to use dfsdm to convert to PCM.
The test code is like below:
HAL_DFSDM_FilterRegularStart(&hdfsdm1_filter0);
uint16_t *pdm_data=...
for (int i=0;i<pdm_size;i++)
{
hdfsdm1_channel1.Instance->CHDATINR = pdm_data[i];
ret = HAL_DFSDM_FilterPollForRegConversion(&hdfsdm1_filter0, 5);
if(ret == HAL_OK){
printf('%d:', i);
pcm_data = HAL_DFSDM_FilterGetRegularValue(&hdfsdm1_filter0, &channel);
printf('filter value: %d, channel:%d\n', pcm_data, channel);
HAL_DFSDM_FilterRegularStart(&hdfsdm1_filter0);
}
}
I think when i =4 ,the
HAL_DFSDM_FilterGetRegularValue can get ok.
Because I set Oversampling=64, SincOrder =DFSDM_FILTER_SINC3_ORDER, so 4*16=64 bit can filter a 16 bit pcm value.
But the real is when i=196, the filter have the result.
when use DFSDM_FILTER_SINC2_ORDER, the i=131.
when use
DFSDM_FILTER_SINC1_ORDER, the i=66.
How dose it work? how many pdm bit to one pcm value when use the config?
The filter config:
hdfsdm1_filter0.Instance = DFSDM1_Filter0;
hdfsdm1_filter0.Init.RegularParam.Trigger = DFSDM_FILTER_SW_TRIGGER;
hdfsdm1_filter0.Init.RegularParam.FastMode = ENABLE;
hdfsdm1_filter0.Init.RegularParam.DmaMode = DISABLE;
hdfsdm1_filter0.Init.FilterParam.SincOrder = DFSDM_FILTER_SINC3_ORDER;
hdfsdm1_filter0.Init.FilterParam.Oversampling = 64;
hdfsdm1_filter0.Init.FilterParam.IntOversampling = 1;
The channel config:
hdfsdm1_channel1.Instance = DFSDM1_Channel1;
hdfsdm1_channel1.Init.OutputClock.Activation = DISABLE;
hdfsdm1_channel1.Init.OutputClock.Selection = DFSDM_CHANNEL_OUTPUT_CLOCK_SYSTEM;
hdfsdm1_channel1.Init.OutputClock.Divider = 50;
hdfsdm1_channel1.Init.Input.Multiplexer = DFSDM_CHANNEL_INTERNAL_REGISTER;
hdfsdm1_channel1.Init.Input.DataPacking = DFSDM_CHANNEL_STANDARD_MODE;
hdfsdm1_channel1.Init.Input.Pins = DFSDM_CHANNEL_SAME_CHANNEL_PINS;
hdfsdm1_channel1.Init.SerialInterface.Type = DFSDM_CHANNEL_SPI_RISING;
hdfsdm1_channel1.Init.SerialInterface.SpiClock = DFSDM_CHANNEL_SPI_CLOCK_EXTERNAL;
hdfsdm1_channel1.Init.Awd.FilterOrder = DFSDM_CHANNEL_FASTSINC_ORDER;
hdfsdm1_channel1.Init.Awd.Oversampling = 1;
hdfsdm1_channel1.Init.Offset = 0x00;
hdfsdm1_channel1.Init.RightBitShift = 0;
