GPIO Always High!

Derek Dosterschill

I am trying to use the expansion header to control a couple motors and auxiliary task mechanism. For this I am using the appropriate pins as GPIO and merely attempting to send high or low signals as needed by the robot. (For instance, I might need the robot to move forward and so I'd send high signals on both sets of pins, whereas if I needed the robot to turn I'd send a high signal to one pin and a low to the other.)

However, the problem is that the pins will only stay high! I've followed the conventions for sysfs just via the terminal, and, although I'm able to set the "values", "active_lows", etc. to 0 or 1, I can't actually get the pins to send 0V. After checking the beagle.h file I used for u-boot it looks like the multiplexer mode is configured correctly. This is also reflected when I get the info from sys/class/gpio/gpio%/% and sys/kernel/debug/gpio. Furthermore I don't get any errors or indication from anywhere that there is something wrong...it just doesn't work!

What should I do? For the first time in my life I have seemingly exhausted the internet...

details:

Beagleboard xm rev c1

ubuntu 12.04

kernel 3.6.8-x4

over 12 years ago

0 Cvetolin Shulev-XID over 12 years ago

TI__Guru 65405 points

Hi Derek,

If you wish to use some pin as gpio the thing which you must to do is to set this pin as gpio in the board file to your board. You could find it the the folder: /u-boot/board/omap3xxx_your_board/omap_your_board.c . Then you must add configuration for the used gpio in the pin mux table. There is an example:

........

MUX_VAL(CP(YOUR_GPIO), (IEN | PTD | EN | M4))

........

then you should use the functions: gpio_pin_init, gpio_pin_write and gpio_pin_read.

Tsvetolin Shulev

0 Derek Dosterschill over 12 years ago in reply to Cvetolin Shulev-XID

Prodigy 30 points

Tsvetolin,

Thank you very much for your reply! Unfortunately, as is explained here, the Beagleboard's pins are controlled via a file called beagle.h, and I've already checked my configuration file to ensure that the pins are in the correct mux mode. Furthermore, I'm using the gpio-sysfs interface for controlling the pins as described here.

The gpio-sysfs files all indicate that it "should" be working, meaning i call0 cat /sys/kernel/debug/gpio and get the appropriate information back. But the voltage (as read by a voltmeter) continues to be 1.8V!

Thanks again,

Derek

0 Cvetolin Shulev-XID over 12 years ago in reply to Derek Dosterschill

TI__Guru 65405 points

Derek,

A given pin may appear in more than one place. Changing the first occurrence may not make the change you want.

The other way is to manage the gpio via console. Look at link which you already read (Getting access to a GPIO and Getting and Setting Direction):

http://www.avrfreaks.net/wiki/index.php/Documentation:Linux/GPIO#gpio-sysfs

The problem seems little bit strange. Let me know if you find a solution.

Tsvetolin Shulev

0 Derek Dosterschill over 12 years ago in reply to Cvetolin Shulev-XID

Prodigy 30 points

Tsvetolin,

Although I appreciate your help very much, it seems that I was indeed using the wrong expansion pins. See, the beagleboard expansion connectors are numbered as depicted here. I had no idea!

Thanks again!

Derek

0 Cvetolin Shulev-XID over 12 years ago in reply to Derek Dosterschill

TI__Guru 65405 points

Hi Derek,

There is a link to the documentation of beagleboard. You should select document according the revision of your board and could check the gpios going to the expansion connector J3.

http://beagleboard.org/hardware/design

Tsvetolin Shulev

Processors

Processors forum

GPIO Always High!