Radio events clock

[Davide]

Hi, I'm doing some measurement on the radio peripheral of the nRF52840 using the generated events and a timer which is set to run at 16MHz. Radio events and Start/Capture Tasks of the timer are managed through the PPI. With such configuration can I expect to measure the time interval between radio events with 1/16MHz accuracy? From some preliminary evaluation I only get a granularity of 8MHz. Any idea?

PS: If useful I'm using SD140 with a connection established.

Thank you, Davide.

[Davide]

I'm quite sure the timer is working properly because on another RADIO event I get odd values, but this is not the event I'm interested in.

I don't have any problem in giving you the source code, but I don't know how to do it.

[Hung Bui]

You can create a case in support portal (my page) and note my name/ link to the case there. Or u can send me a PM with the link to your file on dropbox or google drive.

As I understand , u can see both odd and even value if u test with a simple delay and gpio or other radio event. But u never get odd on that partocular READY and ADDRESS event ? Could that be the nature of the radio ? Can u change the address size and test ?

[Davide]

Yes, I get odd and even values out of the timer in the general case, but the interval between RXREADY and ADDRESS is even 99% of the times: the measurement noise, which is there, doesn't make odd values. I cannot change the address size because I'm working with Bluetooth and softdevice s140, I don't think I can change address size keeping the softdevice working.

I don't know if it can be the nature of the radio, I'm not into CMOS radio design actually...but it wouldn't surprise me if it is (symbol rate is 1Mbit, clock is 16MHz, there may be some rounding somewhere, I don't know).

[Hung Bui]

Hi Davide, Sorry that I haven't got chance to test yet, but I got some information that the radio runs on 4MHz clock (not 100% sure) so the event throwing out is actually on that resolution. This could explain why you only see even value. Could you post some of the counter values you got ?

[Davide]

For what I see in the data I collected, it may be that the radio works mainly at 16MHz (because the interval between RADIO->EVENTS_TXREADY and RADIO->EVENTS_ADDRESS is always 627 ticks), but some time delays or some events seems to be clocked at 8 MHz (the interval between RADIO->(TX)EVENTS_END and RADIO->(RX)EVENTS_ADDRESS it is always even).

Here I copy some of the results for the the interval between RADIO->(TX)EVENTS_END and RADIO->(RX)EVENTS_ADDRESS. Keep in mind that: the values represent 16MHz ticks, and I selected the samples among all the collected ones because the last one is odd.

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