What is the fastest way to manage slave select manually when trying to send 32 bit data over 16 bit SPI with DMA (STM32WB55)?

[SStoy.1]

Hi,

I'm trying to send 32 bit data with DMA over SPI to a slave device with the STM32WB55 which can only be configured to use hardware NSS with 16 bit transfers at most. I understand that I will likely have to pull the chip select down manually, send 16 bits twice consecutively, and then pull the chip select up and repeat. I would have liked to be able to do this automatically without wasting any time as I will be sending a continuous stream of data. However, if I understand correctly, this cannot be done by hardware for the 32 bit case. I am wondering if there is a fast way to do this without constantly polling a flag or something like that as I also want to send the data received back over bluetooth. Any advice/ thoughts would be much appreciated.

Thanks,

SS

[TDK]

If you initiate each transfer, set up a timer in one pulse mode and use one channel to act as the CS signal. Activate the timer just prior to sending data on SPI. If configured correctly (right period/polarity/settings), it will deactivate at the end of the transfer.

To send 32 bits of data, since there is a TXFIFO which can accommodate 32 bits, set it to 8-bit or 16-bit word mode and then write all 32-bits to the DR register. The FIFO will send them out automatically one after the other. (Even if there wasn't a FIFO, you could write 2 16-bit words immediately since the first would be immediately sent to the shift register, generate TXE, and free up the register.)