PDM to PCM via DFSDM getting nothing but static
On the BL47E-IOT01A2 there are two mems microphones (MP34DT01) both connected to DFSDM1_DATIN2. I'm trying to extract the data from just one of those boards and convert it to PCM using a DFSDM filter. I've configured DFSDM Channel 2 to connect to PDM/SPI and trigger on the rising edge, and filter 0 I've configured in one-shot mode, connected to DMA, with an oversampling value of 154, and an integral oversampling value of 3. The internal SPI clock on the board is configured to 1/4 the system clock which is 80MHz, thus the SPI clock should be 20MHz. The code to capture the audio is here:
void HAL_DFSDM_FilterRegConvCpltCallback(DFSDM_Filter_HandleTypeDef *hdfsdm_filter) {
micAudioBuf[micAudioBufIdx] = micRecSample << 8;
micAudioBufIdx++;
if (micAudioBufIdx >= AUDIO_LEN) {
micAudioBufIdx = 0;
audioFilterCplt = TRUE;
} else {
micReset(hdfsdm_filter);
}
}
void micReset(DFSDM_Filter_HandleTypeDef *hdfsdm_filter) {
HAL_DFSDM_FilterRegularStop_DMA(hdfsdm_filter);
HAL_DFSDM_FilterRegularStart_DMA(hdfsdm_filter, &micRecSample, 1);
}And the transmission code is in the main loop here:
while (1) {
// toggle LED2 to indicate activity
HAL_GPIO_TogglePin(LED2_GPIO_Port, LED2_Pin);
// if programming the transmitter
if (audioFilterCplt == TRUE) {
// reset the flag
audioFilterCplt = FALSE;
CDC_Transmit_FS((uint8_t*)micAudioBuf, AUDIO_LEN);
// Reset the mic and start recording again
micReset(&hdfsdm1_filter0);
}
}I'm able to get the data by connecting to the serial port in python, but the output is just static. Here is the code I'm using to capture the output:
import serial
import wave
import struct
import numpy as np
if __name__ == '__main__':
# Replace '/dev/ttyACM0' with the appropriate device path for your system
ser = serial.Serial('/dev/ttyACM1', timeout=1)
# Configure the WAV file settings
num_channels = 1
sample_width = 2 # 16-bit audio
frame_rate = 44100
num_frames = 0 # Will be updated as data is received
compression_type = 'NONE'
compression_name = 'not compressed'
# Create a new WAV file
wav_file = wave.open('output.wav', 'wb')
wav_file.setparams((num_channels, sample_width, frame_rate, num_frames, compression_type, compression_name))
try:
while True:
# Read data from the serial port
data = ser.read(2) # Read 2 bytes at a time (16-bit samples)
if data:
# Unpack the received data as a signed 16-bit integer
sample = struct.unpack('<h', data)[0]
# Write the sample to the WAV file
wav_file.writeframesraw(struct.pack('<h', sample))
else:
break
finally:
# Close the serial port and WAV file
ser.close()
wav_file.close()I'm not sure what else to try at this point