mmc0 stops working after burning boot mode fuses

[brian11]

Hello!

I am working on a board based on the i.MX8MM EVK. Everything was working correctly until I burned the fuses, then the SDIO Wi-Fi module on mmc0 stopped working.

I reproduced the same behaviour on a second board. As with the first board, the Wi-Fi was working fine, until burning the fuses.

The fuses were burned through uuu with this command.

fuse prog -y 1 3 0x1EF02A00

When booting, I usually see this message.

mmc0: Tuning failed, falling back to fixed sampling clock
mmc0: error -84 whilst initialising SDIO card

Before burning the fuses, it would print this instead.

mmc0: new ultra high speed SDR104 SDIO card at address 0001

On one board, it sometimes can start communicating with the Wi-Fi module. The debug output is different every boot. The Wi-Fi module never works in the end though.

Do you have any suggestions of what could cause this?

Thank you,

Brian

[brian11 · Accepted solution]

Hi Brian. We finally managed to fix this! The fuse values were the root cause.

[Binh_Hoang]

Hi Brian11, 

Could you tell me which bit is incorrect? I'm facing the same problem.

Thank you

[brian11]

Hello Brian,

Thank you for your reply. When burning those fuses, I am trying to:

• Set the boot source
• Configure the device to boot from fuses
• Disable JTAG, etc.

Since my initial post, I've compared the SDIO signals. I believe the problem may be a difference in SDIO configuration after burning the fuses.

• Communication only seems to be at 3V3
• There is no change on SD_VSEL

In the oscilloscope screenshot, you can see the first difference. WL_REG_ON is in yellow. The left side is before burning the fuses. The right side is after. I don't know what is happening, but I think this is the first difference in any of the signals.

[brian14]

Hi @brian11, 

I'm working on this case, could you please help me to clarify what you are trying to do burning these fuses?

Based on your errors it seems there are problems with the clocks for the different peripherals.

Have a great day!

Best regards, Brian.