Unable to receive notifications at correct frequency

An update on the status.

I've tried restoring everything to the default  simpleBLEPeripheral.c and only modified SBP_PERIODIC_EVT_PERIOD to 200, 500, 1000. Everything works as expected. What I mean is that I'm getting a notification every 200, 500 and 1000 ms respectively.

So, I decided to try increasing the frequency. I've simply increased the frequency of the periodic event to 20Hz (by setting SBP_PERIODIC_EVT_PERIOD to 50).This means that 2 notifications will be sent in every connection interval, and this is fine.

However, according to the timestamps in btool (and my own btool like java program), I'm only getting 13/14 notifications per second instead of the expected 20. Surely, I can't have exceeded the amount of CPU time? I mean, what is happening in the periodic event is simply read 1 byte from SIMPLEPROFILE_CHAR3 and then writing that same byte to SIMPLEPROFILE_CHAR4, causing a notification to be sent.

I've disabled power savings, so I don't think this is a factor. Also, I've tried the same experiment with connection interval as 50 ms and am getting the same results.

I would really appreciate some help on this!

Hi guys,

I would really appreciate some help on this issue.

Perhaps a simpler question would help.

How do I change simpleBLEPeripheral such that SIMPLEPROFILE_CHAR4 is sending its notifications at 20 times per second? Currently it is only sending 10 notifications per second.

Try using the osal_start_reload_timer() API just once in the SBP_START_DEVICE_EVT and you don't need to touch it in the SBP_PERIODIC_EVT.

 

Sorry, but that didn't help. I am still only receiving 15 notifications per second instead of the expected 20.

In fact, I've tried decreasing the timer interval to only 20ms (for a 50Hz rate) and am also getting 15 notifications per second.

Is there something wrong with the BLE stack?

These are the changes that I made to simple BLE to make use of the osal_start_reload_timer() API. Please advice if I am wrong.

if ( events & SBP_START_DEVICE_EVT )
{
// Start the Device
VOID GAPRole_StartDevice( &simpleBLEPeripheral_PeripheralCBs );

// Start Bond Manager

VOID GAPBondMgr_Register( &simpleBLEPeripheral_BondMgrCBs );

// Set timer for first periodic event
//osal_start_timerEx( simpleBLEPeripheral_TaskID, SBP_PERIODIC_EVT, SBP_PERIODIC_EVT_PERIOD );
osal_start_reload_timer(simpleBLEPeripheral_TaskID, SBP_PERIODIC_EVT, 50);

return ( events ^ SBP_START_DEVICE_EVT );
}

if ( events & SBP_PERIODIC_EVT )
{
// Restart timer
/*if ( SBP_PERIODIC_EVT_PERIOD )
{
osal_start_timerEx( simpleBLEPeripheral_TaskID, SBP_PERIODIC_EVT, SBP_PERIODIC_EVT_PERIOD );
}*/

// Perform periodic application task
performPeriodicTask();

return (events ^ SBP_PERIODIC_EVT);
}

Unfortunately, it is still not working. This is extremely frustrating because it is supposed to be very simple!

  

1. Periodic update task isn't running at the expected rate

I've checked this by incrementing a variable in the periodic event and checking the value after 30s. Bluetooth notifications are enabled after the first few seconds (need time to press the buttons on btool). I am getting the correct result for 10Hz, 20Hz and even 100Hz.

  

2. BLE connection interval isn't what I expect

I don't have an additional board right now to act as a packet sniffer (I can get it next week). So, I've used the GAPRole_GetParameter() to read GAPROLE_CONN_INTERVAL and the result is exactly what I had set it to be.

  

3. Unsychronized interaction between the periodic task and the BLE connection interval

I'm setting my connection interval to 6, which is the minimum. So, hopefully, this isn't an issue.

  

4. Aren't going to get any more than one notification on this characteristic per connection interval

Actually, I've asked in this thread and was told that 3 max-size notifications can be sent in each connection interval. 

  

Just to recap, the current situation is as follows:

I can only get around 15 notifications per second despite setting the periodic event to 20Hz or even 100Hz. Connection interval is set at 6, and I am using the simpleBLEPeripheral sample program that is given. 

Is your problem that you only see around 15 notifications per second reported by BTool, even though you think you are sending them faster? The problem may be that your situation is limited by the dongle and BTool itself. There is a virtual COM port link between the dongle and BTool, and you may just be seeing the effect of bandwidth limitation on this link, or the speed of BTool itself. I think this topic has come up before and I seem to remember this being a limiting factor.

Here is an update on the situation.

I've updated everything to the 1.3 stack and am getting better results.

I can achieve frequencies of 30 Hz reliably.

40Hz is unreliable, it works for the first few seconds and then will start to have a lower and lower rate in which notifications are being received. If I power down the transmitting device, btool would continue to show many notifications. 

I suppose Matthew Kendall is right and that this is a limit of the dongle. I am fairly certain that this is not a problem with btool because I have my own program to parse the received notifications and am getting similar results.

Can I check whether the HostTestApp project that is given is actually the firmware that is loaded onto the usb dongle? I might take a look at it when I have time to see if there is anything that could be done to boost the notification rate.