RE: ppi clearing of event flag

Susheel Nuguru — Fri, 03 Mar 2017 09:40:10 GMT

Good question Akbar,

Look at this Figure that shows you the internal of how Peripheral interface is (a peripheral can be a TIMERx , RTC, RADIO etc)

The event signal that goes to PPI is internal signal from the peripheral AND not the value of EVENT register itself. If you just connect the PPI to the event of the peripheral then

if you have not enabled the interrupts then EVENT register of the peripheral is always set to 1 since you are not clearing it explicitly. But this does not matter because the PPI is using internal signal of the peripheral and it gets only pulses of events.
if you have enabled interrupt for that event, then PPI will not clear the event register (since PPI is getting only a pulse of this event from the peripheral internal signal). The value of the EVENT register (not the internal signal) is the source for interrupt in ARM NVIC. Here you need to explicitly clear the EVENT register, else your interrupt handler will run forever (as long as its interrupt priority will allow it to run).

Is this clear?