BCM20736S slow and inconsistent operation of the fast timer callback

[Anonymous]

I am running a simple application on the BCM20736S, and I am hoping for a fast startup. I am not using BLE at all in my application for  now. It is a long story, but for the moment I am just using the fast timer callback, I2C, PUART and a some simple logic in the code.

My problem is that I see slow and inconsistent operation of the fast timer callback, especially at startup. It gets called a few times a second, sometimes once every few seconds. The rate is currently set to 10ms, which should give me 80Hz call rate for the best case. Here is my debug output where I simply print a counter value from the fast timer interrupt.

Hours:Minutes:Seconds - Counter

15:30:49 - 29

15:30:49 - 30

15:30:49 - 31

15:30:49 - 32

15:30:50 - 33

15:30:53 - 34

15:30:53 - 35

15:30:54 - 36

15:30:54 - 37

15:30:54 - 38

15:30:55 - 39

15:30:55 - 40

15:30:55 - 41

15:31:08 - 42

After I run for awhile, this slow behavior will sometimes go away, and sometimes not. When it is working well, I see a consistent 80Hz rate of timer callbacks. I am hoping for this behavior all the time.

My questions are:

1. Is there a way to turn off the BLE tasks (or other processor hungry tasks) that are keeping the fast timer callback from running? I have a simple application, so do not need BLE at this point.

2. Is this normal behavior for this part? Is there a way to improve it?

Thanks in advance,

     Aaron

[Anonymous]

Hello Aaron,

1.  The BLE Tasks cannot be turned off.

2.  Which application did you start from in your test?

Thanks

JT

[Anonymous]

Hi JT,

Thanks for your quick response.

My application was based on an I2C application, on the I2C temperature sensor, I think.

1. Is it possible to turn off the BLE receiver, so that it does not get any input over wireless?

2. Is it normal for the timer callbacks (fine and 1 second) to be inconsistently called during startup? I am seeing this behavior every time I startup, but sometimes it improves and sometimes it does not.

Thanks,

     Aaron

[Anonymous]

I am still interested in an answer to my question #1 above, but as for question #2:

The timer callbacks seem to be coming much more consistently now that I turned off sleep by the recommended method as:

    // Setup sleep control callback

    devlpm_registerForLowPowerQueries(preventSleep); // Where preventSleep() is a callback that returns 0

I am now getting consistent callbacks! This is critical for my application, and I can live with the greater draw on the battery.

-Aaron

[JacobT_81 · Accepted solution]

If you keep your fine timeout above 12.5ms, you will maintain much more consistency in addition to the ability to enter sleep. You were likely experiencing issues as a result of contention between sleep and the timer. A possible second option is to utilize the patch called bt_clock_based_timer.h which allows for a much lower smaller interval than 12.5ms. Please see the patch for details of its use.

Jacob