Linux/AM3359: GPIO0_20 always low when configured to be input

oren zvuluni

Intellectual 325 points

Part Number: AM3359

Tool/software: Linux

Hi,

I am using beaglebone black with kernel 4.1.12-ti-r29.

i configure gpio 20(gpio0_20) to be input but the value is always 0.

i configured it from the user space with the next commands:

1. $ echo 20 > /sys/class/gpio/export

2. echo in > /sys/class/gpio/gpio20/direction

and when i check the gpio's status, its the output:

gpio-20 (sysfs ) in lo

the state of gpio 20 is always low....why??

thanks,

Oren

over 8 years ago

0 Yordan Kovachev over 8 years ago

TI__Guru**** 161600 points

Hi Oren,

What are you connecting to this gpio? Do you drive it from an external device?

Best Regards,
Yordan

0 oren zvuluni over 8 years ago in reply to Yordan Kovachev

Intellectual 325 points

Now its not connected to anything.

i will connect button but first i need it to be with high value.

Thanks

0 oren zvuluni over 8 years ago in reply to Yordan Kovachev

Intellectual 325 points

Yordan,

I appreciate if you can help me....i am stuck with it for two days...

Thanks

0 Yordan Kovachev over 8 years ago in reply to oren zvuluni

TI__Guru**** 161600 points

Hi,

This depends on which device ball are you using to mux gpio0_20. You should have a look at its reset release state from the Data Manaul.

You can configure this device pad to have its internal pull-up enabled. This will keep the gpio0_20 high, but, depending on your application, you may need to configure the gpio0_20 to active low in your .dts file.

Best Regards,
Yordan

0 oren zvuluni over 8 years ago in reply to Yordan Kovachev

Intellectual 325 points

i already made all of this.

in the device tree i set it as input with internal pullup and i set to mux mode 7 as you can see below:

0x1b4 (PIN_INPUT_PULLUP | MUX_MODE7)

and its still low after i export the GPIO and configure it to input.

0 Yordan Kovachev over 8 years ago in reply to oren zvuluni

TI__Guru**** 161600 points

Can you share your dts?

Best Regards,
Yordan

0 Yordan Kovachev over 8 years ago in reply to Yordan Kovachev

TI__Guru**** 161600 points

Hi,

I tested this on my side. I connected gpio0_26 of my BeagleBone Black to gpio0_26 of my Beaglebone (white).
On BBB settings are:
echo 26 > export
cd gpio26
echo in > direction

On BeagleBone White:
echo 26 > export
cd gpio26
echo out > direction

When I toggle gpio26 value on BeagleBone White (which transmits 0 or 1) the value gets reflected on BeagleBone Black (cat value returns the corresponding 0 or 1). So gpio works when configured as input (I am able to read values on gpio26).

Can you verify that you don't have any pulls on the gpio line that hold it constantly low? Have you verified your pinmux?
Can you test with a different GPIO pin?

Best Regards,
Yordan

0 oren zvuluni over 8 years ago in reply to Yordan Kovachev

Intellectual 325 points

Hey Yordan

I was out of office until today, sorry about the delay in the response.

My Colleague her show me my mistake in the device tree and its working now...

sorry and a lot of thanks about the responses.

Thanks,

Oren

0 Yordan Kovachev over 8 years ago in reply to oren zvuluni

TI__Guru**** 161600 points

Hi Oren,

Glad to hear you've overcome this issue.

Best Regards,
Yordan

Processors

Processors forum

Linux/AM3359: GPIO0_20 always low when configured to be input