[riot-notifications] [RIOT-OS/RIOT] sys/stdio_uart: Add warning about use in ISR (#13985)
notifications at github.com
Sat May 2 22:42:25 CEST 2020
I'm not sure I agree on this.
To me, even simple outputs from UART are an extremely often used tool.
IMO debugging alone makes stdio from ISR an important use case.
```An UART implementation might choose to not guard an atomic sequence of
interactions with the hardware by disabling IRQs but using a mutex, e.g.
because the sequence takes long. Locking a mutex from interrupt
context will result in a deadlock, if the mutex is already locked.```
If some implementations do this, can they be changed?
```If an ISR is triggered from a power saving mode, some peripherals or
clock domains might still be offline during that ISR; including the UART
peripheral. This is a valid implementation choice to allow time critical
low power scenarios being covered by RIOT.```
They might still be offline *after* the interrupt that caused a wakeup.
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