PCF8575 GPIOs

Ganesh Tenka

Other Parts Discussed in Thread: PCF8575

My aim is to access the port pins of PCF8575 I/O Expander or GPIO from userspace .. In the code, in order to write a value i am using system command like this :

sprintf("ucaa_buf","%s %d %s","echo > 0 /sys/class/gpio/gpio",gpionum,"/value");
system(ucaa_buf);

And i dont have any idea, how to read a value from the port pin using the system command as above..

Is there any alternative other than system command??

How to read value of a port pin from userspace??

over 10 years ago

0 Yanko Todorov-XID over 10 years ago

TI__Mastermind 29520 points

Hello Ganesh,

Could you specify your Hardware platform?

PCF8575 driver is in drivers/i2c/chips/pcf8575.c

To see the state of I/O registers in PCF use i2cget command - linux.die.net/.../i2cget

github.com/.../i2cget.c

Best regards,
Yanko

0 Titusrathinaraj Stalin over 10 years ago

TI__Guru** 116100 points

Hi Ganesh,

You can use "cat" linux command to get the value of particular GPIO pin.

I hope, we don't have any other command like "system" and though "system" command is good one.

processors.wiki.ti.com/.../Linux_PSP_GPIO_Driver_Guide

www.ridgerun.com/.../How_to_use_GPIO_signals

0 Ganesh Tenka over 10 years ago in reply to Titusrathinaraj Stalin

Expert 1770 points

Hii Titus,

Actually we can use cat command, but i want to do this from user application program that's why i am asking you for alternative..
I want to toggle an LED connected to GPIO, so what i am trying to do is read that GPIO value into a variable and then if it is 0, i will write 1, if 1 i will write 0...
Also from user application program, for writing the value into a GPIO i can manage that by using
sprintf("ucaa_buf","%s %d %s","echo > 0 /sys/class/gpio/gpio",gpionum,"/value");
system(ucaa_buf);
how can i poll the value of a GPIO??

Thanks in anticipation,

Regards,
Ganesh

0 Ganesh Tenka over 10 years ago in reply to Ganesh Tenka

Expert 1770 points

Hii Titus,
I am able to access from userspace by using the functions in Gpio-int-test.c ..
Thank You

Regards,
Ganesh

0 Titusrathinaraj Stalin over 10 years ago in reply to Ganesh Tenka

TI__Guru** 116100 points

Sounds good.
Thanks for your update.

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PCF8575 GPIOs