Add default 10MHz SD card frequency for SD SPI

[grantwilk]

Related area

SD SPI

Hardware specification

ESP32

Is your feature request related to a problem?

By default, ESP-IDF does not provide a default 10MHz SDMMC speed, even though there is a note about it in sdmmc_common.c. This means that using SD SPI with SD cards that do not support the 20MHz default speed requires additional steps and code modification to initialize.

/* Find highest frequency in the following list,
     * which is below card->max_freq_khz.
     */
    const uint32_t freq_values[] = {
            SDMMC_FREQ_52M,
            SDMMC_FREQ_HIGHSPEED,
            SDMMC_FREQ_26M,
            SDMMC_FREQ_DEFAULT,
            //NOTE: in sdspi mode, 20MHz may not work. in that case, add 10MHz here.
    };

Describe the solution you'd like

Please add a default SDMMC_FREQ_10M definition to sdmmc_types.h and add it to freq_values in sdmmc_common.c.

Describe alternatives you've considered

No response

Additional context

No response

I have checked existing list of Feature requests and the Contribution Guide

• I confirm I have checked existing list of Feature requests and Contribution Guide.

[VojtechBartoska]

Thanks for contributing @grantwilk. Can you please help with triage, @P-R-O-C-H-Y ?

[P-R-O-C-H-Y]

Hi @grantwilk,
This change needs to be made in ESP-IDF. I am in touch with them so once its available, I will let you know :)

[VojtechBartoska]

status update: This feature is now in Review in ESP-IDF.

[igrr]

The feature has been merged and is available on IDF master branch. Note that we don't plan to backport it to release/v4.4, so Arduino project can use it after upgrading to IDF v5.1 in the future.

[P-R-O-C-H-Y]

@grantwilk I have tested 10 Mhz SDMMC on esp-idf-v5.1-libs branch which uses IDF 5.1 and everything works :)
So I am closing this as it's already part of the esp-idf-v5.1-libs branch and will be in 3.0 version of Arduino-esp32.