Can't set modes 1 and 3 in Auxillary SPI(1)

Question

The auxiliary SPI will not accept modes 1, or 3. I’ve enabled spi1-1cs, and /dev/spidev1.0 is created. I can send and receive data but only SPI_MODE_2 and SPI_MODE_0. Setting to mode 3 produces a file error within spidev. The modes work with SPI0, but those chip selects are already occupied and I'd like to try and solve this with software if it's possible.

Does anyone know if this is a limitation with the hardware itself, or is it just a software issue that can be bypassed?

I've posted this question in https://www.raspberrypi.org/forums/viewtopic.php?f=44&t=257145, and am posting it here for some additional eyeballs.

I'm using a pizero with the latest version of raspbian-lite.

Answer 1

Those modes do not work on the Pi's auxiliary SPI peripheral. This was determined by experiment, I don't know if it is documented.

I have not checked to see if it is still the case for the Pi4B (but I doubt the peripheral has been altered).

See my note at http://abyz.me.uk/rpi/pigpio/cif.html#spiOpen

Warning: modes 1 and 3 do not appear to work on the auxiliary SPI

Why not just set chip select yourself?

Answer 2

I confirm that Pi4B has still the same limitation, i.e. modes 1 & 3 are invalid parameters, thus SPI1 can't work in these modes.

Answer 3

I've switched to using SPI6 to use the same pins as SPI1 with less limitations. The only downside is when you enable SPI6 you also have to enable the other SPI channels which can cause conflicts with SPI0 since SPI4 and SPI0 use the same chip enable pins.