I'm attempting to mount an SD card to my STM32F407 with Elm Chan's FATFS using SDIO and f_mount returns FR_DISK_ERR.

The following sequence of functions is called from there:

mount_volume() > check_fs() > move_window() > disk_read()

Ultimately, my error resides in disk_read, more specifically where the SDIO_STA_RXDAVL bit of SDIO->STA never gets raised, meaning there is no data avaialbe in the FIFO to be read, as commented below:

cmd = (count > 1) ? 18 : 17;
t = msTicks;
rd = 0;

SDIO->DCTRL = ((0b1001 << 4) | SDIO_DCTRL_DTDIR);
SDIO->DLEN = (512 * count);
SDIO->DTIMER = (400000);

sta = 0;
if (!send_cmd(cmd, sector, RESP_SHORT, &resp) || (resp & 0xc0580000))   /*!MOD REG?*/
    return RES_ERROR;
SDIO->ICR = (0xFF);
                SDIO_DCTRL_RWSTART  |
                SDIO_DCTRL_DTDIR    |

while (elapsed(t) < 1000) {

    sta = SDIO->STA;

        err("%s SDIO_STA: 0x%08X\n", __func__, (uint)sta);

    if (sta & SDIO_STA_RXFIFOE)

    if (rd == 0 && !(sta & SDIO_STA_RXDAVL))
        continue;      //<<---No data available, so can't get to FIFO

    data = SDIO->FIFO; //<<---Never gets here

    buf[rd++] = data;
    buf[rd++] = data >> 8;
    buf[rd++] = data >> 16;
    buf[rd++] = data >> 24;

    if (rd == 512 * count)

if (rd < 512 * count || cmd == 18)
    send_cmd(12, 0, RESP_SHORT, &resp);

return SDIO->DCOUNT ? RES_ERROR : RES_OK; //<<---Returns ERROR

I think my SD cards are responding alright, especially since the code returns what kind of SD it is (SD2) and the OCR (0x0080FFC0). I also checked CLK and CMD with the scope and they seem to be alright. There is no activity in any of the D[0:3] lines, though.

Why am I getting stuck?


  • \$\begingroup\$ Is there a reason you are not using the driver stack provided by ST? It basically includes FATFS. \$\endgroup\$
    – Justme
    Aug 23, 2022 at 20:23
  • \$\begingroup\$ You mean the HAL library @Justme ? If so, project requires bare-metal \$\endgroup\$
    – mgmussi
    Aug 23, 2022 at 20:44
  • \$\begingroup\$ If so, maybe it also requires re-inventing the wheel? The HAL exists so you can use it or use it as an example for your own code. \$\endgroup\$
    – Justme
    Aug 23, 2022 at 21:37
  • \$\begingroup\$ @Justme I mean, I'm not re-inventing the wheel necessarely. I'm using the FATFS library and Aurelio's code. Also, I know that HAL uses Elm's implementation of the FATFS \$\endgroup\$
    – mgmussi
    Aug 24, 2022 at 10:57

1 Answer 1


My problem was with the hardware. Although I cannot put a finger on what was the problem, I'll guess that the SD adapter was broken or had a weird pinout. Also, having only the internal GPIOs pull-ups (30k to 50k Ohms) was enough and I didn’t need the physical resistors I was adding to the circuit.

Moreover, my breaking points were generating weird results since the SD is a microprocessor itself. Therefore, every breakpoint would influence clocks and couters from the SD and the were messing up my debugging. Once I got them out of the way, the response came out positive using the embedded SD slot that came with my board.

Another problem that I found was that only the FAT32 card was accepted. ExFAT cards did not get recognized, always returning FR_NO_FILESYSTEM. Below the output of all my testing conditions:

Card Type Circuit Type GPIO_PUPDR Response
FAT32 Embedded Circuit Pull-Up FR_OK
FAT32 Embedded Circuit *Pull-No FR_NOT_READY
FAT32 *SD Adapter Circuit Any FR_DISK_ERR
*ExFAT Embedded Circuit Any FR_NO_FILESYSTEM

* The main factors that caused errors on each combination


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