GPIO INPUT FLOATING DEFAULT VALUE

Hi,

Please "cat" the following file and check what the output for pin46 is:

cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pins

It should be something like this:

pin 46 (44e108b8.0) 000000xx pinctrl-single

You would be interested in the two "xx" values. Please compare them versus Table 9-61. conf_<module>_<pin> Register Field Descriptions of the AM335x TRM.

Best regards,
Miroslav

Hi Miroslav,

Thank you for your reply.  I am using linux-3.12.10-ti2013.12.01from package am335x-evm-sdk-src-07.00.00.00.tar.gz,  But the directory 

 /sys/kernel/debug/

is empty. Do you know why?

desmond

Hi Desmond,

Please try this: mount -t debugfs none /sys/kernel/debug/

Best regards,
Miroslav

Hi Miroslav,

Your reply is very helpful. I get the following results, do you know how can I tell the input status of pin 46?

pin 46 (44e108b8.0) 0000002f pinctrl-single

Thank you so much.

desmond

2f means 00101111. If you check Table 9-61 from the TRM, you'll see that this means.

It seems like your GPIO is set as input with pullup/pulldown disabled.

Best regards,
Miroslav

Hi Miroslav,

The pin 46 is GPIO1_14 which is multipexed with pr1_pru0_pru_r31_14, I set the Pad control registers as following:

Bit: 31-7 ---->Reserved Reserved. Read returns 0.

Bit: 6 --->  SLEWCTRL Select between faster or slower slew rate.
0 Fast
1 Slow(1)

Bit: 5 ---->  RXACTIVE Input enable value for the Pad. Set to 0 for output only. Set to 1 for input or output.
0 Receiver disabled
1 Receiver enabled

Bit 4: ---->  PULLTYPESEL Pad pullup/pulldown type selection
0 Pulldown selected
1 Pullup selected

Bit: 3 ----> PULLUDEN Pad Pullup/pulldown enable
0 Pullup/pulldown enabled.
1 Pullup/pulldown disabled.

Bit: 2-0 ---->  MUXMODE Pad functional signal mux select

I set IN4, IN5, IN8 as value 0x37 which means

bit31~7    bit6    bit5  bit4   bit3  bit2-0
0              0        1      1      0     111

It indicates the input pullup resistor is enabled, could you please tell me where is wrong with it?

Thank you!

desmond

Desmond,

(PIN_INPUT_PULLUP | MUX_MODE7) should definitely set the pin configuration to 0x37. Check if you don't overwrite it somewhere else.

The value of 0x2f will be set if you use (PIN_INPUT | MUX_MODE7).

Best regards,
Miroslav

Hi Miroslav,

Thank you very much for your reply. It helps me a lot.

For GPIO 1_14, if I use

cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pins

I always get:

pin 46 (44e108b8.0) 0000002f pinctrl-single

and the value is always 0

Do you know how to check if this pin is overwritten by other staff?

desmond

Hi Miroslav,

I have set GPIO1_14 as 0x37, but I still get value 0(low) when GPIO1_14 is floating but internally pulled up, do you know why?

cat  /sys/kernel/debug/pinctrl/44e10800.pinmux/pins

pin 46 (44e108b8.0) 00000037 pinctrl-single

cat  /sys/class/gpio/gpio46/direction              
in

cat  /sys/class/gpio/gpio46/active_low             
0

cat  /sys/class/gpio/gpio46/value                  
0

Thank you!

desmond

Hi Miroslav,

Just adding info to Desmond's message hoping you can point us to the right direction.

All input GPIOs, including GPIO1_14, read the input voltage properly. The issue is that

the internal pullup resistors are not enabled. It seems to be set in the device tree. Do we need to change

something in the Kernel?

And what is the internal pullup resistance value?

Thanks,

Jose

Hi Miroslav,

Thank you!

Your reply makes me clear about GPIO control value.

Best regards,

desmond