Sharing a SPI bus with an SD card (FATFS) and another SPI Slave

[jgvillap]

Hello, 

I am having a few issues with getting the SD card FATFS example code to share the same bus as another slave I transfer data to. 

I have a few questions:

1) Since, I don't need the two slaves to transfer simultaneously, should I have them use the same SPI instance?

2) What part of the FATFS example needs to be done only once? I want to write to the SD card every 1 second or so, so I split the example code into two functions: sd_spi_start() containing the initializing and the mounting, and sd_write() containing the directory reading, file opening, file writing and file closing. So I was planning on calling sd_spi_start() once and the sd_write() multiple times... is this the correct approach?

3) Right now I am stuck where I write to SD card using sd_write() (Channel 6), write to the other slave using nrf_drv_spi_transfer() , then try to write to SD card again and it just gets stuck (the CS pin just stays low):

Do you have any idea to why this is happening?

[jgvillap]

So I can get it to work if I uninitialize SPI in between SD card SPI transfers and other slave SPI transfers. Since it works I'll move forward with this but if someone has an idea why I have to do this let me know so that I can optimize this further.

[wpaul]

I know that the Nordic SPI controller has a feature where you can tell it what chip select pin to use and it will toggle it automatically when issuing transfers. Are you using this feature?

Having the SPI controller assert the chip select line automatically is handy in that it saves you from having to manually toggle the GPIO pin yourself (there's some savings in code), however it really only works well if there is one slave, because the SPI controller can only control one chip select pin at a time, and each slave has a different chip select line.

If you are using the automatic chip select handling feature, then I could see how you'd have to reconfigure the SPI controller each time you decide to switch from using one slave to another. In that case, I would suggest that you stop doing it that way and manually toggle the chip select lines instead.

If you're not using that feature, then I'm not sure what could be wrong. For my current project I have an SD card and resistive touch controller on the same bus, and I can access both of them without needing to reconfigure the SPI bus in between. I do manually toggle the chip selects though.

-Bill

[jgvillap]

How do I disable automatic CS handling? Do I give config a null Chipselect pin when initializing SPI?