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Why isn't UART TX interrupt being called from within another ISR?

Question asked by Alexander Farley on Jan 29, 2018
Latest reply on Jan 29, 2018 by Alexander Farley

MCU: K22F

 

I have one interrupt (generated by a Processor Expert ExtInt component) configured as Low priority. Inside the low-priority interrupt I want to send some serial port data.

 

I have UART0 configured in interrupt-mode with TX interrupt priority High.

 

Each is working independently: I can send and receive bytes on UART0, and the ExtInt is triggering as expected. However, when I attempt to transmit some bytes inside the ExtInt ISR, I don't see the bytes actually being transmitted until after the ExtInt ISR has completed. Basically, it's working as if the UART0 TX interrupt is actually a *lower* priority than the ExtInt priority. 

 

How is this possible?

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