GPIO Access

May 24, 2011, 12:29:08 PM

#0

lbeck

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GPIO Access

Hi All,

I've built a 2.6.30 kernel with GPIO sysfs support. Works well but there are a few pins I can't get to: PB16, PB17, PB18, PC4, PC5, PC9, PC10 and PC11. When I attempt to "export" to these pin addresses using the sysfs mechanism I get an error. I know that some are used by the sound device, which I have disabled in the kernel config. That didn't seem to free up the pins. Looking through the kernel sources trying to find out which I can use is proving exhausting.

Can anyone offer any hints here? I realize I probably won't be able to get to all of these pins but a few more would be nice.

Thanks,

Lance

May 26, 2011, 01:54:11 AM

#1

admin

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Re: GPIO Access

The best thing is to enable and disable the GPIO at driver level. But if necessary it is possible to just enable it from user space by writing to PIO enable register, for example using devmem2 utility,

devmem2 0xfffff600 w 0xc03f3fff

will enable PB0 ~ PB13, PB16~PB22, PB30~PB31 as GPIO.

This should work for kernel 2.6.30 but may not work for kernel 2.6.33 and up as kernel driver will rewrite the PIO enable register with its stored value at some point no matter what's been written to from user space.

September 29, 2011, 02:40:16 PM

#2

AwareWolf

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Re: GPIO Access

I have a similar desire as lbeck: to get at PB16, PB17, and PB18.

I would have thought finding the right kernel config element and turning it off was the right way to go. By simply writing to the PIO register at run time; is that really a good idea?