GPIO in the kernel: an introduction [LWN.net]

GPIO in the kernel: an introduction

Posted Dec 15, 2016 11:07 UTC (Thu) by bla (guest, #112986)
In reply to: GPIO in the kernel: an introduction by nybble41
Parent article: GPIO in the kernel: an introduction

Ok, you c a n set a combined interrupt mask and query the pin state in the ISR on an RPi, but gpio_get_value seems to have latency, which makes this approach pretty much useless in conjunction with switch bounce and the ISR time constraints.
For implementing long button presses, detecting the first flank and reading the level with a thread after some delay seems to be the better approach, it also doesn't require a state change to trigger the long press signal.

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GPIO in the kernel: an introduction

Posted Dec 15, 2016 20:05 UTC (Thu) by BlueLightning (subscriber, #38978) [Link] (2 responses)

Surely the answer to switch bounce is to do the debouncing in hardware?

GPIO in the kernel: an introduction

Posted Dec 15, 2016 20:32 UTC (Thu) by pizza (subscriber, #46) [Link] (1 responses)

But hardware debounce would require adding extra $0.02 worth of components and growing your board size by 2 square millimeters.

Why spent that money on every unit when it can be done once, "for free" in software?

GPIO in the kernel: an introduction

Posted Dec 17, 2016 6:44 UTC (Sat) by flussence (guest, #85566) [Link]

Fun trivia: this is exactly what the NES Classic does. In their GPL code dump there's a kernel driver for the controller - it has the same wire protocol the Wiimote uses (internally!), but leaves the kernel to deal with all that hardware-related insanity and more.