topic Re: i.MX28 Bootstrapping GPIOs in i.MX Processors

i.MX28 Bootstrapping GPIOs

ChristophG_Baum — Thu, 16 Apr 2015 07:55:02 GMT

Hi all,

on a custom board I use the pin SSP0_DATA4__GPIO_2_4 as a reset pin for some external devices. For this purpose the bootloader (U-Boot) initializes this pin as output with level '0'.

Checking with a scope showed that the pin is pulled high right from the start for about 400 ms and the gets low as soon as U-Boot kicks in.

I know that this pin can belong to the SD card interface. But my board boots from SPI NOR.

Could it be that the boot ROM initializes any possible boot interfaces and then checks the bootstrapping pins which one it should actually use?

Regards,

Christoph

Re: i.MX28 Bootstrapping GPIOs

art — Thu, 16 Apr 2015 09:18:05 GMT

The reason of such behaviour is that, by default (immediately after reset), this pin (as well as many other pins) is configured as GPIO input with 47kOhm on-chip pull-up enabled.

Have a great day,
Artur

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Re: i.MX28 Bootstrapping GPIOs

ChristophG_Baum — Thu, 16 Apr 2015 09:38:46 GMT

But wouldn't this be represented by the appropriate bit in HW_PINCTRL_PULL2? The reference manual states that this register is all zero on reset.