SD card via SDMMC instead of SPI?

[perlix]

Grüezi Phil,

Triggered by the wiki page about SPI and I2C, I wondered if you ever considered to access the SD card over the fast SDMMC bus instead of SPI. The Audiokit datasheet suggests that the SD slot is connected to all 6 pins of ESP32's SDMMC_HOST_SLOT_1 (2, 4, 12, 13, 14 and 15, all with pullup resistors).

Using the SD_MMC library, I verified that SDMMC 1-bit mode (using GPIO 2, 14 and 15) is almost twice as fast as SPI. (Couldn't get the even slightly faster SDMMC 4-bit mode working, so GPIO 4 and/or 12 may not actually be connected on my kit).

This is just an idea. I don't even know if SD speed could ever become a bottleneck for audio projects, but if a board's internal wiring allows it, I always prefer using the SDMMC bus.

[pschatzmann]

Yes, I confirm that this is working and nothing is stopping you to use this: Maybe I should add a chapter in the Wiki. Will you share you the setPins() settings that you used, so that I can add them to the documentation ?

I developed this project as an 'add on' to my AudioTools library for which I prefer solutions that work across different microcontrollers.

So far I was not running into any performance issues that made me reconsider my approach...

[perlix]

Thanks, that makes sense.

SDMMC pins are fixed (cannot be remapped). For 1-bit mode: 2 DATA0 14 CLK 15 CMD

So I changed your sdbegin.ino example to:

#include "AudioKitHAL.h"
#include "SD_MMC.h"

AudioKit kit;

void setup(){
    pinMode(2, INPUT_PULLUP);
    pinMode(15, INPUT_PULLUP);
    Serial.begin(115200);
    if(!SD_MMC.begin("/sdcard", true)){    // 1-bit mode
        Serial.println("Card Mount Failed");
        return;
    } else {
        Serial.println("Card Mount Success");
    }
}

void loop() {

}

[pschatzmann]

I thought thats what the following methods are for:

• bool setPins(int clk, int cmd, int d0);
• bool setPins(int clk, int cmd, int d0, int d1, int d2, int d3);

But if I got you right this is not needed because the AudioKit uses the correct default pins...

[perlix]

Correct. SD_MMC.begin doesn't accept pin specifications anyway (because they're fixed).

[pschatzmann]

added example