Global Clock on nRF51822?

[Nick]

Seems like the timer API uses low priority interrupts. Now, I dont need the timer triggers to be exactly delivered so that is fine ... however, i do need to know the exact time between current and last timer trigger. Is there a way to query a clock tick counter or some kind of global counter which i can use to calculate the time elapsed between timer events?

Thanks!

[Håkon Alseth]

Hi,

Are you going to use a timer to track time? Like having a variable that shows minutes/seconds/ms/etc?

If you use the app_timer library, you can setup functions that are called every x millisecond. Using this you can setup a global variable that is incremented (in the app_timer callback function) each time it's called.

Best regards Håkon

[Bastiaan]

Hmm, not really, its for an integration of a gyroscope signal. I do 100 samples / millisecond so looking for something on the order of microseconds if possible.

The problem i see is that, if say the app_timer interrupt was pushed back due to a high priority interrupt (like BLE stack) it would cause delayed calls to the timer interrupt handler.

[Guest]

Hmm, not really, its for an integration of a gyroscope signal. I do 100 samples / millisecond so looking for something on the order of microseconds if possible.

The problem i see is that, if say the app_timer interrupt was pushed back due to a high priority interrupt (like BLE stack) it would cause delayed calls to the timer interrupt handler.

[Håkon Alseth]

You can use TIMER1 or TIMER2 for this. It's sourced by the 16M, so it should give you a good enough resolution.

One thing I'm a bit concerned about is the real-time requirements that you have. As you are already aware of it seems, the stack will block the main application for a given time based on how often and how much data you are sending.

How often is the gyro-sampling-routine called? I know you sample x samples each ms, but I assume it's not sampling every 10 us for eternity?