What is correct way to reassign PPI channel?

[TomWS]

I have a case where I'm using a timer/counter as a counter with one PPI channel routing a GPIO rising edge to the COUNT task. Another GPIO rising event controls the counting in the following way: The first GPIO event STARTS the counter. A GPIO event interrupt handler counts the number of GPIO events and after 'n' of these, I want the next GPIO event to STOP the counter (or, at least, CAPTURE the counter value).

Can I initialize the second PPI channel to connect the GPIO event to the counter START and then, after I've reached 'n' events, simply reassign the PPI channel to connect the GPIO event to the counter STOP (or CAPTURE) task?

Do I need to have an intervening channel disable/enable sequence?

Update: I am using the nrf_drv_ppi driver.

Thanks in advance. Tom

[Susheel Nuguru]

You can do it, just use nrf_drv_ppi_channel_free and allocate the freed channel to the STOP task using nrf_drv_ppi_channel_alloc again. I would suggest you to use an already free channel just to keep the design simple.

[TomWS]

Thanks for the fast reply! I'm surprised that I need to free the channel and go through the allocation process again. Can I do this within the GPIOTE handler (which is where I'm counting the second GPIO pin transitions)?

The simplified schematic of the PPI makes me think that I only need to replace the TEP address in the channel control.

Tom Update: I missed your second suggestion. I like this suggestion as it does keep the design cleaner. I presume in this case, I would allocate and assign both channels at initialization, one to START and one to STOP and then selectively enable/disable depending on where I am in the process.

[Susheel Nuguru]

i am sorry, you were right, looking at the implementation it shows that it is just enough to use nrf_drv_ppi_channel_assign and change the end points for this channel.