• https://community.onion.io/topic/298/need-help-for-https-github-com-onioniot-gpio-test
• https://community.onion.io/topic/369/gpio-access-with-interrupts-and-sys-class-gpio
  I have been doing more work on trying to get interrupt handling of GPIO pins working.

Using build of relevant packages using information covered in:

• https://wiki.onion.io/Tutorials/Cross-Compile
• And also https://community.onion.io/topic/396/some-observations-on-https-wiki-onion-io-tutorials-cross-compile

I have built (and I believe successfully installed) .ipk packages for:

• gpio-irq - see: https://github.com/OnionIoT/gpio-irq
• gpio-test - see: https://github.com/OnionIoT/gpio-test

However, while I believe I have got further than before, I am still having some problems.
Specifically running gpio-test 0 (which should detect a change on GPIO pin 0) does not appear to work (even though I can independently verity that the input state on GPIO pin 0 does change appropriately). I get the output:

• Waiting GPIO 0 signals...

and no further output.

However, I do note the following possible issues in relation to gpio-irq:

1. There is the following comment in the README.md file for gpio-irq:
   • Needs kernel patch <a href="https://github.com/GBert/openwrt-misc/tree/master/gpio-test/src/patches-3.14">728-MIPS-ath79-add-gpio-irq.patch</a> by GBert to function.
     Does anyone know whether or not this patch is part of the kernel on the Omega?
2. The gpio-irq package needs to be installed using opkg -force-depends ... since it reports that a later version of the kernel is required - this may be related to the previous point
   Does anyone have any info on this too?

Thanks in advance for any responses

The code in gpio-test has the following:

• fd=open("/sys/kernel/debug/gpio-irq", O_WRONLY);
  if(fd < 0)
  {
  perror("open");
  return false;
  }

  sprintf(buf, "+ %d %i", gpio, getpid());

  if(write(fd, buf, strlen(buf) + 1) < 0)
  {
  perror("write");
  close(fd);
  return false;
  }

This code appears to run OK with no errors and should have written to the file /sys/kernel/debug/gpio-irq - this file exists and appears to have the correct access rights, yet after running the code, this file is empty.

This file should (once gpio-test is running) have the contents:

• + n p where n is the GPIO pin number and p is the process id

On termination of gpio-test it should have contents:

• - n p where n is the GPIO pin number and p is the process id

Yet the file appears to never change

For the record, I did the following:

1. Applied this patch to the OpenWrt sources (as in https://wiki.onion.io/Tutorials/Cross-Compile)
2. Built a release using these sources including gpio-irq (i.e. kmod-gpio-irq) and gpio-test packages
3. Copied the file openwrt-ar71xx-generic-onion-omega-squashfs-factory.bin from the
4. Installed the built release on my Omega using sysupgrade openwrt-ar71xx-generic-onion-omega-squashfs-factory.bin
5. Ensured gpio-irq (i.e. kmod-gpio-irq) and gpio-test were installed from the .ipk files generated above
6. Ran gpio-test N & (where N is the GPIO pin number) and observed that interrupts were detected and reported when the state of pin N was changed
7. Wrote a small amount of C code that used similar techniques to gpio-test and checked that it too correctly intercepted the interrupts.

The only relevant observation I can make is that because of this line:

• int err = request_irq(irq_number, gpio_edge_interrupt, IRQ_TYPE_EDGE_BOTH, "gpio_irq_handler", data);

in gpio-irq.c the interrupt is triggered on both the rising and falling edge. The specific case can be detected from the state of the pin when the interrupt code is called. I may consider a patch that allows setting for rising or falling edges specifically, but it is not a big deal.

As a consequence, I would HIGHLY RECOMMEND to the Omega people that, in the next (or relatively soon) release of the Omega code, the patch (https://github.com/GBert/openwrt-misc/blob/master/gpio-test/src/patches-3.18/739-MIPS-ath79-add-gpio-irq-support.patch) be applied and that package kmod-gpio-irq be included.
Then, GPIO interrupts will be standardly available in the Omega without additional work.

Thanks!

A relevant comment is that in playing with code based on gpio-test I have found:

• There is only a single irq handler that can be installed using the existing code

• BUT amongst the information passed to the irq handler is a structure that in one of its fields gives both the pin number for which the handler is called and the state of the pin - with this, it will be easy to write some code that:

  • Calls on to an additional handler specific for an individual pin
  • Can distinguish between rising and falling changes in the pin

  I will be updating my new-gpio code to incorporate GPIO pin interrupt handling capabilities based on this.

Some interesting information about how the kmod-gpio-irq code works is:

• It works by detecting writes (in user mode code) information about the pin number and the process id to /sys/kernel/debug/gpio-irq to enable and disable interrupt handling for the pin
• When interrupt handling for a pin is added by writting to /sys/kernel/debug/gpio-irq the following line is created in /sys/kernel/debug/gpio (e.g.for pin 6):
  • gpio-6 (GPIO IRQ handler ) in lo
• This line is removed when the interrupt handler for the pin is removed

As an aside, the default contents of /sys/kernel/debug/gpio are :

• gpio-8 (USB power ) out hi
  gpio-11 (reset ) in lo
  gpio-27 (onion:amber:system ) out lo

Of these:
a. I don't understand why gpio-8 is there (????)
b. gpio-11 makes sense since pin 11 is the reset pin
c. gpio-27 makes some sense since I understand that pin 27 is the Omega LED

This is NOT meant to be a complaint or hurry up, but do you have any rough idea when the updated with GPIO irq support as per the patch will be available?

The reason I ask is that I have now got some significant C/C++ code (as an extension to the new-gpio code I posted some time ago) that from my testing appears to work well in handling GPIO interrupts.

This includes a test program that in a very simple manner can be used to set a background program running that, on an interrupt (e.g. a button press), will run any shell command specified at the time the program was started. Thus allowing running of any command to be associated with a button push - multiple such instances can be set up - one for each GPIO pin if so desired.

However, this code is dependent upon:

1. A kernel version with the above patch
2. Installation of the kmod-gpio-irq package

I would like to post this code since I believe it would be of general use, but there is no point in doing so until the update is generally available.

The first issue is that there is no kmod-gpio-irq that I require - it is not available via opkg even after doing an opkg update - so I tried installing the version I had built using the OpenWrt cross compile environment (and which worked with the patched system image I had built and installed).

I think i have tracked the problem down to the fact that there is no /sys/kernel/debug/gpio-irq file. The GPIO irq handling works by writing to this file.

I am trying to track down what I had installed in my separately compiled image that would have created this file.

If you have any info on this, I would be interested to hear. meanwhile, I will try to keep working to track down what is different between the latest Omega build (for which GPIO irq does not work) and the system build that I produced (for which GPIO irq works)

I'm probably about to take a break (it's getting to be evening here) - if I don't here anything more from you on this, I will keep looking tomorrow.

Btw, I made the gpio-test package available in the Onion package repo.

Happy hacking!

I am currently on firmware b264 so will shortly upgrade and try again. Will report back when done

Have upgraded to b266 and everything works perfectly - including my GPIO IRQ and test program.

My IRQ code is basically an extension to the code I have previously posted for new GPIO access (https://community.onion.io/topic/143/alternative-c-code-for-gpio-access) with the addition of IRQ handling capabilities.

Because it may be of use to others, I will do the following:

1. Send the test program and needed library with some basic documentation on its use in a separate post
2. Later, update the package and details in https://community.onion.io/topic/143/alternative-c-code-for-gpio-access with the latest sources and full documentation