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CC2642R: Scanning multiple peripherals with low connection interval

jerome d.
Expert 1355 points

Part Number: CC2642R

Hi All
I'm following up this previous thread https://e2e.ti.com/support/wireless-connectivity/bluetooth/f/538/t/959539.

My app requires latency as low as possible, as it exchanges MIDI over BLE, in addition to this, my central should be able to connect to 4 peripherals at the same time.
In order to follow my latency specification, the central is set with conn interval min 7.5ms and conn interval max 15ms, peripheral latency = 0

Any connection update from the peripheral is rejected, and central sends connection update requests to peripherals.

I played with scan interval/window/duration in order to find the best strategy to scan new peripherals while already in connection with other peripherals.
What I found is as follow :

I'm using scan window = 2.5ms, scan interval = 5ms, scan duration of 2,5sec, if no peripheral is found, and if there is room to add one more peripheral, the scan is restarted.
I can connect easily to 4 peripherals when they are all advertising while the central is switched on.
Once all 4 connections are active, if I switch off one peripheral, then switch on again, my central has some difficulties to find it again.

What I observe in the above situation is, sometimes the MR_EVT_SCAN_DISABLED is not received after the scan duration has passed, or it is received much later than expected.
Any idea what could cause this issue ?

Also, in my special case (keep latency as low as possible, support up to 4 peripherals), what would be the best strategy regarding scan interval/window/duration ?
Thanks to all.
 

  • 0
    TI__Guru** 101490 points

    Hi Jerome,

    To begin, it would be interesting for you to see how much free time the radio has. To do so you can map the RF output to a pin (please see the debugging guide for details).

    jerome d. said:
    What I observe in the above situation is, sometimes the MR_EVT_SCAN_DISABLED is not received after the scan duration has passed, or it is received much later than expected.
    Any idea what could cause this issue ?

    This is probably because the stack does not manage to schedule the scan command (because the radio is not available)

    jerome d. said:
    Also, in my special case (keep latency as low as possible, support up to 4 peripherals), what would be the best strategy regarding scan interval/window/duration ?

    What is the advertisement interval on the peripheral side? Could you try to decrease it?

    Best regards,