SD card library speed selection

RE: SD card library speed selection

Einar Thorsrud — Fri, 22 Aug 2025 12:53:05 GMT

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)?

RE: SD card library speed selection

Alexandre Desgagne — Tue, 19 Aug 2025 13:50:57 GMT

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,

RE: SD card library speed selection

Turbo J — Tue, 19 Aug 2025 12:54:34 GMT

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

RE: SD card library speed selection

Alexandre Desgagne — Tue, 19 Aug 2025 12:37:04 GMT

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.

RE: SD card library speed selection

Alexandre Desgagne — Tue, 19 Aug 2025 12:33:02 GMT

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