[riot-notifications] [RIOT-OS/RIOT] [GPIO] - External interrupt (#16801)

Jean Pierre Dudey notifications at github.com
Thu Sep 16 15:04:54 CEST 2021

Hello  @ksadura !

>Is there any infinite loop implemented in this method, that makes a program working constantly? After I put this method into the int main() function, my programme was kept alive.

Depends on the board/cpu you're using, sometimes using a pin that is not supported to be initialized as an interrupt will an `assert` checking for that will be reached.

>Second question, I think more crucial to me, is whether a callback function (passed as an argument to this method) executes on the different thread than the rest of code or not. I had a case, when in the callback function I was sending an IPC message - msg_t to the another thread, let's call it THREAD2. When my pin was interrupted for the first time, callback function executed on the thread with proccess ID (kernel_pid_t) equaled 1. Then, after second thread received IPC message and executed its code on the thread with ID = 2, any next pin interruption caused, that callback function always executed on the same thread as THREAD2 with ID = 2. Why there was no thread disitinction between those two processes?

The callback function is executed on an ISR context which is a good idea to keep these callbacks simple enough to not introduce any latency into the system and keep real-time guarantees.

The PID for messages sent from an ISR is [`THREAD_PID_ISR`](https://api.riot-os.org/group__core__msg.html#gadba0f57bc141ce3a7ec95fbd4bf26429) which is calculated at compile time, however if you try to get the pid of an ISR with `thread_getpid` you'll probably get the PID of the last scheduled thread (I'm not sure though).

To send a [`msg_t`](https://api.riot-os.org/structmsg__t.html) from an ISR you can use [`msg_send_int`](https://api.riot-os.org/group__core__msg.html#ga2762c096056c5eac7ffe38c8727e033a).

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