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?

[awneil]

In general (not specific to Nordic), I would always try to avoid sharing an SD-Card with any other SPI device.

I don't really that SD-Cards are designed to share their SPI interface.

jgvillap said:

What part of the FATFS example needs to be done only once?

I don't know if the FatFs design assumes that it has exclusive control of the SPI lines.

You'd probably have to check that with ChaN: 

http://elm-chan.org/fsw/ff/00index_e.html

http://elm-chan.org/fsw/ff/bd/

[jgvillap]

Damn, I didn't know that SD-cards were designed to have its own SPI bus. It's kind of too late now though since my custom board has space for only one bus. I will take note of that for future revisions.