How does radio behave if HFXO is not stable?

RE: How does radio behave if HFXO is not stable?

Hung Bui — Mon, 17 Jul 2017 11:49:56 GMT

Yes, my typo again. Really sorry for that :(

You are correct, it varies that's why Stian have to make an assumption of 1.5ms as of worse case. If you start the radio before the HFXO is ready, of course it's high chance that the signal from the radio will be corrupted, deviated. If in your application, the radio need to be turned on at an exact point in time, my suggestion is to setup the timer to wake CPU up before the radio needs to be on about 1.5ms. Then start HFXO, then put the CPU back to sleep. Wake up again when the radio need to be on, check if HFXO is running, if yes then start the radio, if not, skip that event (or wait longer if there is not real time requirement). You need to have the rough estimation of worse case scenario on how long the HFXO takes to start.

RE: How does radio behave if HFXO is not stable?

Turbo J — Sun, 16 Jul 2017 09:17:54 GMT

Not tested, but it will probably just ramp up to the wrong frequeny that may be even outside the 2.4-2.5GHz range.

RE: How does radio behave if HFXO is not stable?

butch — Fri, 14 Jul 2017 15:01:11 GMT

Thanks. You mean "the radio will proceed even if the HFXO is not started." (I think you have a typo, you said "even if the radio")? I have found that the HFXO startup time DOES vary among boards, as much as 1.2msec. In my low-power application, I need to schedule the radio for a certain time, and must wake up before that to start the HFXO. So I need to know what the radio will do if I start the HFXO but for any reason it is not running stably when I start the radio. You have answered that the radio will proceed, but not what the likely errors are. I suppose I can test that myself.

RE: How does radio behave if HFXO is not stable?

Hung Bui — Fri, 14 Jul 2017 14:30:20 GMT

Sorry, my typo, please read as NRF_CLOCK->EVENTS_HFCLKSTARTED = 1.

The thread you point to is not "Most examples from Nordic " :)

In that thread Stian had to use an assumption of 1.5ms because he was doing estimation for power consumption.

The Radio doesn't care about the crystal if it's stable or not, it's the application who have to take care of that.

It will proceed even the HFXO is not started.

RE: How does radio behave if HFXO is not stable?

butch — Fri, 14 Jul 2017 13:48:13 GMT

This post in this forum is an example that discusses that the SD waits 1.5ms devzone.nordicsemi.com/.../

My question is about the HFXO clock, not the LF clock. Another way of phrasing my question: does the radio wait for the HFXO to be stable, or does it proceed anyway but probably not perform as well (CRC errors).

RE: How does radio behave if HFXO is not stable?

Hung Bui — Fri, 14 Jul 2017 10:54:38 GMT

Hi butch,

Could you point to which example that we use a delay for fixed amount of time ?

Usually we stay in a loop waiting for NRF_CLOCK->EVENTS_HFCLKSTARTED = 1. Please have a look at the examples\peripheral\radio example.

Of course the waiting loop can be replaced by CPU sleeping waiting for the interrupt (that's what we do in our softdevice).