Two SD card interfaces over SPI.

[Sreejit]

I have a working code to get FatFs running with SD card over SPI0 interface on a nRF52840 DK. I wanted to know if it is possible to add another SD card with FatFs on SPI2 interface and access the cards in the same firmware. The file, nrf_block_dev_sdc.h has the following at line 54.

/**
 * @brief Active SDC block device handle. Only one instance.
 * */
static nrf_block_dev_sdc_t const * m_active_sdc_dev;

Is it possible to work around this?

[Edvin]

Hello,

Due to summer holidays we are very short staffed these weeks. I have not had time to handle all my cases. I will get back to you as soon as possible. Hopefully tomorrow. 

A genera hint: Perhaps you need to use only one instance, but switch it between the two SD card readers?

Best regards,

Edvin

[Sreejit]

Alright. The spi instance is selected in the file app_sdcard.c. So I was thinking of duplicating this file and separating all the enums, structs and the functions.  Lemme know what you think.

[Edvin]

It is not certain you need to do this. Perhaps you should either use one instance of nrf_block_dev_sdc_t and switch it between the SD card readers that you are using?

I think I would start by expanding:

    // Initialize FATFS disk I/O interface by providing the block device.
    static diskio_blkdev_t drives[] =
    {
            DISKIO_BLOCKDEV_CONFIG(NRF_BLOCKDEV_BASE_ADDR(m_block_dev_sdc, block_dev), NULL)
    };

To contain twi DISKIO_BLOCKDEV_CONFIG().

Then, in order to use the other disk, you would e.g. call disk_initialize(1), which will point to the other disk.

But from there I am not certain. The fatfs is an external library, so I am not familiar with it. It looks like one instance of FATFS fs, which is used in f_mount(&fs, ...) mounts one drive, so you need to figure out how to make this mount drive 1 instead of drive 0. I see that FATFS has a member called drv, but I don't see how this opens drive 0 by default.

[Sreejit]

Hi Edvin.

Thanks for your answer. I went ahead and duplicated the files, app_sdcard.c/.h and nrf_block_dev_sdc.c/.h and other data structures in nrf_block_dev.h . It seems to work fine for now. This will need some thorough testing though.