SWRU626 December 2025 CC3501E , CC3551E
PDM channel FIFOs are organized as 2x24-bit. It can store variable number of samples depending on sample size and configuration of PDM for single mono, dual mono or stereo operations. DMA trigger or CPU interrupt is generated based on FIFO threshold setting. The value of FIFO threshold has different meaning depending on the number of samples that can be stored in the PDM channel FIFOs.
In the case of single mono configuration with 8-bit sample size, both FIFOs are combined to provide 12 entries in the FIFO. Valid threshold values are from 0 to 11. When threshold is set to 0, event is generated once first element is filled in the FIFO. When threshold is set to 11, event is generated when all 12 elements are filled in the FIFO.
In the case of single mono configuration with 16-bit or 24-bit sample size, both FIFOs are combined to provide 4 entries in the FIFO.. Valid threshold values are from 0 to 3. When threshold is set to 0, event is generated once first element is filled in the FIFO. When threshold is set to 3, event is generated when all 4 elements are filled in the FIFO.
In the case of dual mono or stereo configuration with 8-bit sample size, both channel FIFOs operate independently and each channel FIFO provide 6 entries to store the samples. Valid threshold values are from 0 to 5. When threshold is set to 0, event is generated once first element is filled in the FIFO. When threshold is set to 5, event is generated when all 6 elements are filled in the FIFO.
In the case of dual mono or stereo configuration with 16-bit or 24-bit sample size, both channel FIFOs operate independently and each channel FIFO provide 2 entries to store the samples. Valid threshold values are 0 and 1. When threshold is set to 0, event is generated once first element is filled in the FIFO. When threshold is set to 1, event is generated when both the elements are filled in the FIFO.