GPIO Am335x SDK7

Rainer Berns

I set a gpio pin to mux7 and high level output in u-boot. During the kernel start (between message "Starting kernel ..." and "booting Linux") the level changes to low and input. Later on I can modify it with sysfs (mux stay at 7).

I have checked the dts and dtsi files but the gpio pin is not manipulated. Is there any function in the kernel which sets all gpios to a default setting ?

Is it possible to set the output level inside the dts files.

Thanks in advance

Rainer

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi Rainer,

Speaking of "low and input" are you referring to the padconf register for this pin, or the GPIO registers?

0 Rainer Berns over 9 years ago in reply to Biser Gatchev-XID

Prodigy 190 points

Hi Biser,

I check the level at the pin with an multimeter and osciloscope and with the sysfs gpio registers. After changing direction to "out" in sysfs i can set the level to high.

Rainer

0 Ivan Matrakov over 9 years ago in reply to Rainer Berns

TI__Expert 4475 points

Hi Rainer,

The u-boot finishing with reading an device tree file am335x-evm(xx).dtb from a boot partition. When the kernel start booting the setting from am335x-evm(xx).dtb file are applied. Are you sure that in the am335x-evm(xx).dtb file this gpio not changing his setting. Please see the configuration in the corresponding am335x-evm(xx).dts file.

BR
Ivan

0 Rainer Berns over 9 years ago in reply to Ivan Matrakov

Prodigy 190 points

Hi Ivan,

I have checked it. Do you kown which function in the kernel sets the gpio settings defined in the dts files ?

Is it correct that gpios which are not defined in the dts files are normally not touch by the kernel ?

Regards

Rainer

0 Ivan Matrakov over 9 years ago in reply to Rainer Berns

TI__Expert 4475 points

Hi Rainer,

No one place for manipulating with device tree. Every device use this information when is needed. But it is very likely, the kernel when booting to make a software reset of all drivers and this gpio to stay in a default state. For that reason could you test with a other gpio (if it's possible).

BR
Ivan

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GPIO Am335x SDK7