PDM microphone driver for PSoC 6 on Zephyr
Finished 2026
A driver that gets the PDM microphones on Infineon's CY8CKIT-062S2-AI kit working under Zephyr, using the vendor's low-level library instead of ModusToolbox.
The problem
Zephyr 4.3 has no upstream PDM or DMIC driver for the PSoC 6 audio block, so I wrote one. It builds with plain west: no ModusToolbox, no proprietary IDE, no cyhal.
The trick is that Zephyr already ships Infineon’s lower-level library (the PDL) as a west module. I call cy_pdm_pcm, cy_gpio and cy_sysclk from it directly and add the PDL source file to the CMake build.
How it works
The kit has two IM72D128V01XTMA1 microphones. The clock pin is P10.4 and the data pin is P10.5, both muxed to the PDM function (HSIOM 21), and the data pin needs a pull-down, not high-impedance.
The clock chain is in the diagram below. The 100 MHz FLL feeds HFCLK1, which doesn’t run unless you turn it on: Zephyr’s devicetree leaves it off, so a board overlay enables it from the FLL. Three divide-by-4 stages take it down to a 1.5625 MHz mic clock, which is inside the microphone’s 1.0 to 3.072 MHz range, and a sinc decimation filter turns the bit stream into about 16 kHz of 16-bit PCM. The audio block’s clock gate also has to be enabled by hand.
The code reads back the pin mux at boot and logs it, and it dumps a few raw FIFO words so you can tell a floating line from a live one. The demo loop takes 100 ms frames (1600 samples), logs the minimum, maximum, average and energy of each, flags a frame as TRIGGERED when the energy goes over a threshold, and toggles an LED.
Build and flash:
west build -p always -b cy8ckit_062s2_ai/cy8c624abzi_s2d44 .
west flashIt’s about 400 lines in total and Apache-2.0 licensed. It’s mono, since only the left microphone is read, and it polls the FIFO instead of using DMA, throwing the frame away if the FIFO overflows. It isn’t a Zephyr DMIC-API driver: it has its own small init and read functions. The repo has no saved capture, so there are no plots here, but it does run on the board.