AM572x VDDSHV8 and SD card boot

Hein Thet Aung

Hi,

I have a custom board designed by following the GP EVM. When I tried to boot from the SD card, vddshv8 goes to 2.98V and the board cannot boot.

Could you advise me what could be a possible problem?

I could run Hello World program on A15_0 using Jtag in CCS.

Thanks,

over 8 years ago

0 Biser Gatchev-XID over 8 years ago

TI__Guru**** 393215 points

Hi,

What is the SD card power supply? Where is VDDSHV8 taken from?

0 Hein Thet Aung over 8 years ago in reply to Biser Gatchev-XID

Intellectual 280 points

Hi Biser,

Thank you for your quick response.

VDDSHV8 is powered by LDO1 of TPS6590376ZWSR PMIC and the power for the SD card is taken from the 3.3V swich which is also turned on by the PMIC according to the power up sequence.

Regards,
Hein

0 Biser Gatchev-XID over 8 years ago in reply to Hein Thet Aung

TI__Guru**** 393215 points

Do you have anything else powered by LDO1 besides VDDSHV8?

0 Hein Thet Aung over 8 years ago in reply to Biser Gatchev-XID

Intellectual 280 points

No, I don't have.

Regards,
Hein

0 Biser Gatchev-XID over 8 years ago in reply to Hein Thet Aung

TI__Guru**** 393215 points

I'm sorry, I can't help on this. Suggest you check your schematic and layout very carefully.

0 Biser Gatchev-XID over 8 years ago in reply to Biser Gatchev-XID

TI__Guru**** 393215 points

Especially check if the VDDSHV8 trace on the PCB is wide enough.

0 Hein Thet Aung over 8 years ago in reply to Biser Gatchev-XID

Intellectual 280 points

Thank you for your time and advise.

Regards,
Hein

0 Ahmad_Rashed over 8 years ago

TI__Genius 13567 points

Hi Hein,

The MMC driver in Linux is setting the VDDSHV8 line to 3.0V intentionally. What you are experiencing is the SD card speed negotiation failure - it boots at default and then the MMC driver negotiates speed and voltages. Since you are using a UHS-1 card then VDDSHV8 goes from 3.3V to 1.8V. For some reason during the negotiation it fails so the correct behavior is to power off/on the SD card and negotiate again (our GP EVM doesn't have this hardware so it just doesn't boot). I'm don't know why but the MMC driver sets VDDSHV8 back to 3.0V after failing instead of 3.3V. Actually it goes to 0V first temporarily then to 3.0V and this signal could be used to enable/disable a load switch connected to the SD card's VDD.

The easiest work around is to try another UHS card or try a non-UHS card. Internally the SW team has a list of SD cards tested.

You could also disable other UHS modes so the MMC driver won't attempt to negotiate to them. This is done in the device tree (dts) file.
&mmc1{
/delete-property/ sd-uhs-sdr104
/delete-property/ sd-uhs-sdr50
/delete-property/ sd-uhs-ddr50
/delete-property/ sd-uhs-sdr25
/delete-property/ sd-uhs-sdr12
};

0 Hein Thet Aung over 8 years ago in reply to Ahmad_Rashed

Intellectual 280 points

Hi Ahmad,

Thank you for your explanation. The SD Card can boot with the GP EVM. That explains the problem could also be within the layout and routing of my custom board which cause the speed negotiation problem. I will try to disable the other UHS modes and also try with a non-UHS card.

Regards,
Hein

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AM572x VDDSHV8 and SD card boot