Today I started first work with STM3F0 series (F030, in 20 pin tssop. Should be useful for small things, and very cheap).
After setting SPI to 8 bit mode, a single uint8_t write to the SPI_DR will write *two* bytes. (first your byte, and then a blank byte). Looking into this a bit, the SPI controller works somewhat differently on these, and seems to ignore what it is set to if you write 16 bits to it. If that makes sense. So, for reference, spi_send function: void spi_send <https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#ga1fcf7661af69bcf8999ae3f6d102fd8b>(uint32_t spi, uint16_t data) { /* Wait for transfer finished. */ while (!(SPI_SR <https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#gae14de4e25f63b18a43dc0f20bdc4fe8e>(spi) & SPI_SR_TXE <https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#ga5bd5d21816947fcb25ccae7d3bf8eb2c> )); /* Write data (8 or 16 bits, depending on DFF) into DR. */ SPI_DR <https://libopencm3.github.io/docs/latest/stm32f1/html/group__spi__defines.html#ga9e95e2b653dfa3add622205d9cb0ddb5>(spi) = data; } Since data is a uint16_t, it writes 16 bits to the SPI_DR, which it interprets as two 8bit transfers on a 'F0, apparently. Doesn't matter if you pass a uint8_t to spi_send(); nor does the following work: uint8_t data = 0x55; SPI_DR(spi) = data; as SPI_DR() must return a _16 bit_ pointer. I guess GCC then promotes your 8 bit uint to a 16 bit one. The only thing that seems to work, is to have an 8 bit pointer to SPI_DR, something like this: uint8_t *spi_8ptr; spi_8ptr = (uint8_t *) &SPI_DR(spi); while (SPI_SR(spi) & SPI_SR_BSY); *spi_8ptr = data; Though that will break 16bit transfers... Not sure what the best way to fix this is? Anyone else work with SPI on F0? I guess there could be SPI_DR8(); and SPI_DR16(); but that's a little hokey... as all the higher level functions will need to be either duplicated in 8/16 versions, or have a 8/16 bit argument breaking everything. Anyway, that is all for now mark
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