can you clarify some of the documentation eg SPI size parameter doesnt specify bytes or words

[mmalex]

This is a documentation bug/request really, but I recently was trying out the HAL_SPI functions for the first time, and had set up the peripheral for 16 bit transfers.

The documentation for HAL_SPI_TransmitReceive and related functions, for several of the families, across several documents and pdfs found on the internet and ST's site, all simply say that the size parameter 'Size: amount of data to be sent and received'

I found a number of erroneous exmaples that use sizeof(buffer), as well as several question on this forum with incorrect information; for the record, from reading the HAL code, the size is measured in units of 16 bits (or whatever your SPI is configured for). while that makes total sense, I wish the docs made this clearer as it tripped me up - and many others. I was overrunning my buffer by a factor of 2, leading to bizarre behaviour, faults etc.

took a while to unpick.

For the DMA functions, I dont know yet if the size of the DMA transfer configuration (half word or word) matters... I will find out the hard way I guess, as the docs are silent on the matter 🙂

I hope this helps someone - SPI_Transmit size is measured in words, not bytes 🙂

(The same documentation scarcity is true for I2S and SAI peripherals also, for what it's worth... I haven't stumbed into other areas yet)

[S.Ma · Accepted solution]

Actually there are at least 4 versions of the SPI IP.

The original is 8 or 16 bits

The V2 has programmable bit size

The V3 has 32 bit FIFO, and that's where the way to write the DR has meaning, if SPI is 8 bit, writing 16 bit result in 2x8 bit sent.

Only when focusing at performance (lowest clock frequency or lowest bus congestion) these things become under the vision range.

[mmalex]

interesting! thanks for the extra information. I think that increases even more the need for more documentation around what the 'size' parameter means 🙂 since it doesnt specify any detail at all at the moment.

thanks!

[RMcCa]

Another good reason to ditch hal and deal with the peripheral registers yourself. In the F7, one specifies the source and destination data width and the number of dma transfers. I don't know about how it behaves when the 2 data widths are different but in my code 8 half word(16 bit) dma spi reception works exactly as one might expect.​