Do spi_xfer and SPI_read/write play well with each other?

[JerryR]

I have a project that is attempting to use both SPI_xfer AND SPI_read/write commands with their own setup_spi and #use spi. They don't appear to work together. Should they?

Thanks group

[jeremiah]

"Should they" is more of a philosophical question. They aren't designed to work together at all. spi_write() and spi_read() are intended to only work with designs that use the setup_spi() method to configure the SPI. spi_xfer() is used for both reads and writes and is intended to only work with designs that use the #use spi() directive. Generally you pick one or the other but do not mix them.

[JerryR]

jeremiah:

Thanks for your reply and interest in my question. OK, that's what I thought. I'll have to modify my code to use only one or the other SPI communications method.

Many thanks!

[Ttelmah]

The key is if you look at the manual, #use spi, only refers to spi_xfer. spi_read/write, both only refer to setup_spi.

The older method only offered setup_spi, and only supported hardware SPI.

The newer method is #use, which supports a lot more options with spi_xfer, including multi byte support, streams, and hardware/software.

There shouldn't be any problem converting code that uses spi_read/write to spi_xfer. A search and replace should be able to change the code in a few seconds.

[JerryR]

Ttelmah:

Yes, already doing the search and replace dance. Had a lot of code using both methods, Using hardware SPI.

Thanks and best regards

[oxo]

The help file isn't clear on how to do multibyte transfers using spi_xfer.

It doesn't look like I can pass an array of 8 bytes to it. Presumably the way to do this is with 8 x calls to spi_xfer.

[Ttelmah]

Why would you expect it to be able to access an array?.
Functions that do this, need pointers rather than simple variables.
spi_xfer can do 4 bytes at a time if you work using int32's.

Just create a wrapper function, but remember you are then also going to have to handle the returns if you want to read as well.