How to set a GPIO as output in u-boot without glich?

Technical Support
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1

Hello,

I have modified u-boot to change the MUX for specific pins (44 and 91), there are set as GPIO output open drain from board_early_init_f.
Then in board_late_init, I also set these GPIO using gpio-request and gpio_direction_output(xx, 1).

My issue is that between MUX setting and gpio_direction_output, the PDOR bit for these gpio is set to 0 (default boot value), so the pad is driven to 0 for a short time.

What is the proper way to fix that glich?

  • Should I change mux after I have used gpio_direction_output?
  • Should I change PDOR in board_early_init_f?
  • Is there another cleaner way to set PDOR bit as the same time the IOMUX register is set?

Thanks in advance for your help

2

hi guillaume

what is duration of the glitch? What is connected at the output of these pins?

3

Hi,

The glitch is around 100ms. On the GPIO there is a 10K pull-up to 3V3.
If I let the GPIO in high impedance, there is no glitch.
I will try to set the PDOR value before changing the IOMUX register but I’m not sure what I have to use to do it. Is clr/setbits_le32 the right functions to use, or should I use raw_read or direct memory access in C?

Regards

4

Hi,

Sorry I just get it. The pull-up is missing … due to a disconnected board.
So everything work as expected.

Regards

5

Perfect, that it works. Thanks for the update.