Is there any documentation on the SDMMC_STA_STBITERR bit?

[JKiel.1]

We are using an eMMC Card with the STM32l476VE MCU.

I don't think it is relevant, but the eMMC is the Micron MTFC8GAKAJCN-4M IT TR.

We are having intermittent failures in HAL_MMC_ReadBlocks() in which SDMMC_CmdReadSingleBlock() returns SDMMC_ERROR_CMD_RSP_TIMEOUT(4).

If we check the SDMMC_STA register (hmmc->Instance->STA) before the call to SDMMC_CmdReadSingleBlock(), the SDMMC_STA_STBITERR bit (bit 9) is set.

According to the Reference Manual (RM0351 rev 9.0 2021-06-29), bit 9 of the SDMMC status register is reserved.

This bit is not mentioned in the datasheet for the STM32l476VE.

The only documentation is the comment in the Header file "/*!<Start bit not detected on all data signals in wide bus mode */".

The code was generated with STM32CubeMX V6.4.0 using STM32Cube FW_L4 V1.17.1

At no place in the code is the SDMMC_STA_STBITERR bit checked.

Is there any documentation on the SDMMC_STA_STBITERR bit?

When does this bit in SDMMC_STA get updated?

Is there any way in software to recover from this error?

If this *MUST* be fixed in hardware, what should we be looking for?

Does it make sense that this condition is causing SDMMC_CmdReadSingleBlock() to return SDMMC_ERROR_CMD_RSP_TIMEOUT?

We just found out that a similar error is happening very intermittently with SDMMC_CmdWriteSingleBlock() returning SDMMC_ERROR_CMD_RSP_TIMEOUT(4).

[Amel NASRI]

Hi @JKiel.1​ ,

I confirm that the bit 9 in SDMMC_STA is reserved as described in the reference manual so SDMMC_STA_STBITERR needs to be removed from stm32l476xx.h.

Internal ticket number: 125969 (This is an internal tracking number and is not accessible or usable by customers).

-Amel

[gfuehrer]

I recently experienced this bit being set, and I came here to learn about it, but this is all I could find searching for SDMMC_STA_STBITERR.

It would be nice if someone knowledgeable about the SDMMC peripheral in the L4xx series would answer the OP's questions, since I have the same ones. Is that possible?

It was never a question whether or not it is considered reserved. And we know that it does something in this peripheral, possibly even matching it's name Start Bit Error. The headers in STM32Cube_FW_L4_V1.18.0 have already changed the #define for SDMMC_STA_STBITERR to be in a separate section commented as "Legacy", but not the matching SDMMC_ICR_STBITERRC.

My feeling is that this bit on the L4xx should be documented and, if there's a problem with it, discuss that in the errata.

Thanks for listening,

-Gary