MSP430F6747A: Communication with eMMC MTFC8GAM through SPI interface

I have never used an eMMC card but I have used a 64MB MMC card. A long time ago. The protocol for that was different than for an SD card. While it was similar, unless the SD card code had been specifically written to fall back to an MMC setup, it would fail.

We've compared both SD and MMC standard, while the response format does differ indeed it looks like the command format is similar for the master (6 bytes command, with command index and CRC7 for the last byte).

Issue is the eMMC is not responding at all, it would have been nice to at least get an response from it that tells the command we sent was invalid.

Another difference with MMC is that they really leaned into that multi-drop bit. Their outputs begin in an open collector/drain mode so  you must have a pullup resistor.

Looking at some of my old code, you should get a response to CMD0.

Yes we've got pull-up resistor on all the eMMC data lines and CMD line as well.

Your code look very similar to ours, here what our command sending function looks like :

static void sdSpiSendCommand(unsigned char *res, unsigned bufferLength)
{
    unsigned tries = 0;
    unsigned char crc = 0;
    unsigned i;

    // sdCardCommand.command is the command id, 0 for init, 24 for write block etc
    // sdCardCommand.params is an uint32_t containing the command arguments
    const unsigned char rawCommand[5] = {
        0x40 | sdCardCommand.command,
        (sdCardCommand.params >> 24) & 0xFF,
        (sdCardCommand.params >> 16) & 0xFF,
        (sdCardCommand.params >> 8) & 0xFF,
        sdCardCommand.params & 0xFF};

    pinClear(SDCARD_CS); // Assert CS line to low level

    for (i = 0; i < sizeof(rawCommand); i++) {
        crc = crc7Tab[(crc << 1) ^ rawCommand[i]];

        // sdSSpiSendByte() both write a byte then read one which is returned
        sdSpiSendByte(rawCommand[i]);
    }

    sdSpiSendByte((crc << 1) | 0x01); // send CRC-7 followed by end bit

    do {
        if (++tries > SD_CMD_RESPONSE_TIMEOUT) {
            pinSet(SDCARD_CS);
            sdStatus |= SDCARD_CMD_TIMEOUT;
            return;
        }
        res[0] = sdSpiSendByte(0xFF);
    } while (res[0] == 0xFF); // There is a pull-up on DAT0, which means 0xFF is read if nothing is sent by the eMMC

    // Usually for MMC format, command response is 6 bytes
    for (i = 1; i < bufferLength; ++i) {
        res[i] = sdSpiSendByte(0xFF);
    }

    pinSet(SDCARD_CS);
}

When this function is called, it never reaches past the do-while loop, we're not getting anything back and we end up with an error.
On the oscilloscope the DAT0 line is constantly at logic level high due to the pull-up.

Do you see anything wrong with this code ? (This used to work with SD card)