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Can CC2540 achieve 30ms latency?

Lihong
Prodigy 100 points
Other Parts Discussed in Thread: CC2540, CC2541

We need to communicate biderectional from our device to iPad through bluetooth with minimum acceptable latency of 30-50ms (4 Byte MIDI message from our device to iPad every time, message can occur at any time) at all time. 

It is said on the web that the latency can be adjust by tuning baud rate and connection interval at the cost of more power consumption. More power consumption is OK to us, and realtime response is our major focus. I wonder if CC2540 can get the 30ms latency. What is the minimum latency of CC2540 under this circumstance?

And I was told that Bluetooth 2.1+ EDR or Bluetooth 3.0+ HS achieve lower latency than BLE 4.0. Is that true?

  • 0
    TI__Guru 57865 points

    Hi Lihong,

    The minimum connection interval for Bluetooth low energy is 7.5 ms. I would however recommend at least 10ms, either way you are good to go :)

    Best Regards.

  • 0 in reply to J Lindh
    Intellectual 440 points

    Hi Joakim,

    As I understood Lihong have meant another thing and I also interesting in this question. The thing is not in latency between two packets it's in the hole system latency. For example on BLE CC2541 device you have a button and on iPad you have a light on the screen, if button is pressed the light on the screen will blink. So what is the latency of system response between button press and blink? The latency I assume will be = OSAL time + TI BLE stack processing time + data transition + Apple BLE stack processing time + iOS response. Of course we want to know here the "OSAL time + TI BLE stack processing time + data transition" part, it's minimum possible time and how to obtain it. I assume some low level stack commands can help? Thank for advice.

    |---------------------|                                                                          |------------|
    | CC2541 Device |      <------ Response time? --------->      |     iPad     |
    |---------------------|                                                                          |------------|

    Regards

  • 0 in reply to Dmitry Cheremisin
    TI__Guru 57865 points
    Hi Dmitry,
    Much have happened since this thread got updated the last time. Generally, 30ms is the minimum connection interval for iOS interaction unless MIDI or HID is the intended connected device (special rules apply to that, which allows shorter connection intervals). The added processing time you refer to will impact the latency and it's very dependent on the system design.

    The button press will not transmitted OTA until the connection event. This means that throughout the connection interval, the packet could be queued up at any point. However, if the interrupt comes close to the connection event, it may be saved for the next connection event which introduces an added latency equivalent to the value of the connection interval.

    Either way, from the CC2541 perspective, connection interval is the crucial parameter. For the iOS side, it's more complex as it's a black box ....unfortunately.

    Best Regards
    Joakim