SD card library speed selection

[Alexandre Desgagne]

Hi, 

I'm developing a project that requires to write GPS data to an SD card. I'm using Nordic SD card library.

I'm able to initialize and interact with the SD card only if I'm setting both APP_SDCARD_FREQ_INIT and APP_SDCARD_FREQ_DATA to 536870912 (2 MHz). I'd like to reduce this speed, but when I do so, I'm not able to initialize or interact with the SD card. Even the library documentation recommends to reduce the SPI frequency to 250kHz during initialization.

Here's my settings:

#define APP_SDCARD_ENABLED 1
#define APP_SDCARD_SPI_INSTANCE 0
#define APP_SDCARD_FREQ_INIT 536870912
#define APP_SDCARD_FREQ_DATA 536870912

SDK version: 16.0.0

I'm using an nRF52832 and SPI0 instance.

Do you have an idea of what could cause this issue?

Alexandre

[Alexandre Desgagne]

Note that the SD card communication is also working when setting both init and data frequencies to 4MHz.

[Alexandre Desgagne]

I tried setting the INIT frequency to 2Mhz and DATA frequency to 500kHz and this is working too. It feels like the problem is only at initialization.

[Turbo J]

Use oscilloscope.

Note that SD card init requires a pullup on MISO, or that you enable the internal one in the NRF chip. The card powers up in open drain mode.

Careful: Cards from different manufacturers can vary in SPI mode behaviour

[Alexandre Desgagne]

Hi, 

I tried setting NRFX_SPIM_MISO_PULL_CFG to 3 (Pull up) and setting init speed at 125Khz, 250kHz, etc. but still working only at 2Mhz and 4Mhz.

This setting is used in nrfx_spim.c (266 to 276).

// - MISO (optional) - input,
if (p_config->miso_pin != NRFX_SPIM_PIN_NOT_USED)
{
    miso_pin = p_config->miso_pin;
    nrf_gpio_cfg_input(miso_pin, (nrf_gpio_pin_pull_t)NRFX_SPIM_MISO_PULL_CFG);
}
else
{
    miso_pin = NRF_SPIM_PIN_NOT_CONNECTED;
}
p_cb->miso_pin = p_config->miso_pin;

I found that post that looks pretty much like my issue too.

 SD Card FATFS example not working at low init frequency, but does work at higher frequencies 

Do you think I need to configure MOSI and CS pull up too?

Thanks, 

[Einar Thorsrud]

Hi,

I am wondering what is actually happening in the communication here. Can you share a logic analyzer trace of the SPI lines in a working and non working case (for isntance 2 MHz and 250 kHz)?