About the behavior of the nRST signal at SD Boot with i.MX6UL

[yuuki]

Dear all,

We made a board using i.MX6UL.
We use SD Boot.

However, after Bootloder started, the system stops.

We confirmed each signals.
After Bootloader started, nRST signal becomes Low when Kernel starts.
Therefore we found that SD_3V3 became OFF.

We confirmed each signals in SD Boot with EVK board.
In EVK board, similarly, nRST signal becomes Low.

However, SD_3V3 does not become Low because there is C1706.

Therefore I understand that EVK board does not have a problem.

When Kernel starts, why does nRST signal become Low?

Would you tell me the method avoiding this?

Best Regards,
Yuuki Murasato

[igorpadykov · Accepted solution]

Hi Yuuki

seems this is caused by uboot (please check attached mx6ul_14x14_evk.c) codes:

#define USDHC1_PWR_GPIO    IMX_GPIO_NR(1, 9)

..

int board_mmc_init() :

..

gpio_direction_output(USDHC1_PWR_GPIO, 0);

udelay(500);

gpio_direction_output(USDHC1_PWR_GPIO, 1);

C1706 helps to distinguish between power cycle (long ~5ms pulse)

and short -RST card hardware reset signal (equivalent to cmd0 command).

In general one can try to comment these codes.

Best regards

igor

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