Re: GPIO and interrupt
Ahmad Fatoum <[email protected]>
| Newsgroups | org.kernelnewbies.kernelnewbies |
|---|---|
| Message-ID | <[email protected]> |
Hello Tony, On 26.07.23 12:10, Tony He wrote: > Hi, > > I'm writing button driver. The button is based on GPIO.When the button > is pressed or released, the interrupt is generated. According to the > GPIO value(1 or 0) , I can know which action is taken(pressed or > released). > However, a question occurred to me. Do I need to consider when to get > the GPIO value? I mean is it possible that GPIO value will be changed > caused by another interrupt when I get the GPIO value in top or bottom > half > of first interrupt? I know the CPU is fast and pushing/releasing > button is slow, so it should not happen in practice. But let's just > consider this case in theory. You can assume the button is pushed or > released very very fast. This is not only a theoretical issue. The transition from button being pressed to unpressed and back is not noise free, so a naive translation of IRQ/GPIO state to input events may not be sufficient. Dealing with this is called debouncing and involves taking multiple samples before signalling the input event. > Seems that GPIO interrupt is special comparing with other device with > cache. There is no cache to store data(GPIO value) for GPIO. Right? > Can someone help to clarify this question? Thanks a lot. IRQ handlers have a second argument with a pointer to device specific data. You can store information there and many drivers do so. You need to take care that the data isn't accessed concurrently though, e.g. via a spinlock. You can see how all this is implemented in the Linux gpio_keys driver. Cheers, Ahmad > > Tony > > _______________________________________________ > Kernelnewbies mailing list > [email protected] > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ Kernelnewbies mailing list [email protected] https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies