Advanced users • Is everyone happy with the quality of libgpiod?

Foreword: Not sure this belongs under Advanced Users (apologies if inappropriate choice).

And so, after experimenting briefly with libgpiod and its spawn (the gpiod collection) 18-24 months ago, and reading more frequently about the impending demise of sysfs w linux 6.6 - I decided to take libgpiod out for another spin. And not wanting to invest much time in writing a C app, I used the gpiod collection as a proxy.

So far, my impression is that libgpiod is "lacking". Following are a few simple examples:

From the command line:
1. Apparently the developer still has issues with persistence:

• $ gpioset gpiochip0 25=1
  $ gpioget gpiochip0 25
  0
  $
  < OK, no surprises here, and I get that not everyone feels that when something is "set", it should remain set until it is cleared. >

2. Let's go on...

• $ gpioset --background gpiochip0 25=1
  gpioset: can't daemonize in this mode
  < ?? No mention of this in man gpioset, but turns out 'signal' is the correct mode for using 'background' >
  $ gpioset --mode=signal --background gpiochip0 25=1
  $ gpioget gpiochip0 25
  gpioget: error reading GPIO values: Device or resource busy
  < ?? it seems the way this must be done is as follows: >
  $ ps -aux | grep gpioset
  pi 2212 0.0 0.0 1980 84 ? Ss 04:30 0:00 gpioset --mode=signal --background gpiochip0 25=1
  $ kill 2212
  < but of course now, this should be obvious >
  $ gpioget gpiochip0 25
  0
  $

3. But it turns out that what seemed to be going on - may not be what's actually happening in the hardware... Let's connect an LED from GPIO24 (pin 18) to GND (pin 20) & see what happens:

• $ gpioset gpiochip0 24=1
  < LED comes ON, and stays on !! >
  $ gpioget gpiochip0 24
  0
  < LED turns OFF immediately after gpioget command >
  < sorry, but this doesn't quite make sense to me >
  < also fairly sure this is not how it worked last time I tried (~18-24 mos ago) >
  $ gpioset --mode=time --sec=3 gpiochip0 24=1
  < LED comes ON, and stays on indefinitely >

Maybe I'm thick... is there something going on here that I'm missing - or does this behavior seem strange to others?

Statistics: Posted by irishmonk-57 — Mon Dec 18, 2023 7:12 am

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