How to find GPIO number to enable from user space

bhagya raja90

Part Number: PROCESSOR-SDK-AM437X
Other Parts Discussed in Thread: AM4378, SN75HVD12

Tool/software: Linux

Hi friends,

I am working on a custom board based on AM4378. I am using SDK ti-processor-sdk-linux-am437x-evm-02.00.00.00. UART5 is using for RS485 communication in half duplex mode and D24 pin for rts and dts pins..

I am trying to enable /disable the gpio0-19(D24) from user space, with the following commands

echo 19 > /sys/class/gpio/export

echo "out" > /sys/class/gpio/gpio19/direction

echo "in" > /sys/class/gpio/gpio19/direction

echo 1 > /sys/class/gpio/gpio19/value

echo 0 > /sys/class/gpio/gpio19/value.

I could see the GPIO19 toggling (from terminal), but the voltage levels at pin D24 pin is still low only even if i set high.

I have used the formula( (32*M+N)) to calculate gpio number for gpio0-19, so i tried with echo 19 > /sys/class/gpio/export. Is that formula correct ? if so why i amunable to see voltage changes at D24 pin.? I have changed the dts files also

....

gpio0_pins_default: gpio0_pins_default {

pinctrl-single,pins = <

0x270 (PIN_OUTPUT_PULLUP | MUX_MODE7) /*(D24) xdma_event_intr0.gpio0[19]*/

};

gpio0_pins_sleep: gpio0_pins_sleep {

pinctrl-single,pins = <

0x270 (PIN_OUTPUT_PULLUP | MUX_MODE7) /*(D24) xdma_event_intr0.gpio0[19]*/

};

.......

........

&gpio0 {

status = "okay";

pinctrl-names = "default","sleep";

pinctrl-0 = <&gpio0_pins_default>;

pincntrl-1 = <&gpio0_pins_sleep>;

gpios = <&gpio0 19 GPIO_ACTIVE_HIGH>;

};

....

Thanks in advance.

over 7 years ago

0 Cvetolin Shulev-XID over 7 years ago

TI__Guru 65405 points

Hi Bhagya,

When a pin (D24 for example) is configured for MUX_MODE7 (UART5) it is not correct to try to use it as GPIO.

BR
Tsvetolin Shulev

0 bhagya raja90 over 7 years ago in reply to Cvetolin Shulev-XID

Prodigy 60 points

Hi Tsvetolin Shulev,
Thank you so much for your quick reply.
D24 pin is used as gpio only to send 1 or 0 to the converter SN75HVD12(rs485) where RTS and CTS pins are connected together to operate it in half duplex mode. if we send 1 from D24 , then its acts as transmitter and 0 as receiver. so what i want here is how can i set 1 or 0 for D24 which i have configured as GPIO. in mode7 its name is gpio0-19. I would like to know its equivalent gpio number so that i can use this commands from userspace.
echo XX > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpioXX/direction
echo "in" > /sys/class/gpio/gpioXX/direction
echo 1 > /sys/class/gpio/gpioXX/value
echo 0 > /sys/class/gpio/gpioXX/value.

what is XX value for gpio0-19 signal ???

0 Prabhakar Lad over 7 years ago in reply to bhagya raja90

Guru 11260 points

Hello,

If you are setting the pin as input you wont see a transition you need to supply voltage levels.
Firstly set the GPIO pin as output and when you set value 0/1 scope the pins and you should see it.

echo 19 > /sys/class/gpio/export
echo "out" > /sys/class/gpio/19/direction
echo 1 > /sys/class/gpio/19/value
After doing this scope value
echo 0 > /sys/class/gpio/19value
After doing this scope value

Cheers,
--Prabhakar Lad

0 bhagya raja90 over 7 years ago in reply to Prabhakar Lad

Prodigy 60 points

Hi Prabhakar,
Thanks for you time. I want to know gpio number for GPIO0_19 pin for am437x board. I have seen the formula to calculate the gpio number for (GPIOm_n = 32*m+n) for am437x. Thats y i have used "19" for GPIO0_19. i set it in output and send 1.But i could not see the voltage changes on the board. Is that formula correct? or do i need to change anything on pinmux and device tree files in am437x-gp-evm.dts file ??

0 Prabhakar Lad over 7 years ago in reply to bhagya raja90

Guru 11260 points

Hello,

Yes the gpio numbering is correct GP0[19] if what you want. even from the formulae you can get (GPIOm_n = 32*m+n) ((GPIO0_19 = 32*0+19) = 19). Yes you need to configure the pinmux to behave the pin as GPIO.

Cheers,
--Prabhakar Lad

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How to find GPIO number to enable from user space