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RTOS/CC2640: Connection Events Length

Steffen Rentz
Intellectual 370 points
Part Number: CC2640

Tool/software: TI-RTOS

Hi,

On our CC2640 hardware we did some power measurements with connection events and observed 2 things:

1. The length of a connection event increases if there is a slave latency. With a Connection Intervall of 4000 ms and Slave Latency of 2 a Connection Events takes about 3,69 ms.

With a Connection Intervall of 1000 ms and Slave Latency of 0 a Connection Events only takes about 1,83 ms.

Can anyone explain if this is a normal behaviour and why?

2. An empty Connection Event takes the same time as an event carrying data of the temperature sensor. I have implemented that sensor data is only updated via BLE if it changed (compared with the last measurement). On the first sensor measurement the data is sent with the next connection event. In room conditions the temperature stays very constant and so on the next measurement there is nothing to update and the next Connection Event is empty. The Packet Sniffer shows the expected result: packet length of 0x15 for a Connection Event with sensor data and packet length of 0x0c for an empty PDU.

However power & time measurements of these Connection Events show the both events need the same time and consume the same power. This is not what I had expected as my code change was supposed to save power.

Does anyone know why this is so?

Regards

Steffen

  • 0
    TI__Guru** 105180 points
    Hello Steffen,

    The increase in time can be attributed to sleep clock accuracy requirements. This will accumulate during longer effective connection intervals requiring an earlier wake up.

    What equipment are you using to measure power? If you are not using a DC power analyzer such as the one used in app note SWRA478 for measuring power consumption, you might not be able to see the 1us / bit increase in time. Note that the overhead for a CE is also a factor and may further explain your results.

    Best wishes
  • 0 in reply to JXS
    Intellectual 370 points
    Hi JXS,

    Thanks for your reply. We are using exactly the same Keysight Power Analyzer as in SWRA478.
    Can you explain why an empty Connection Event has almost the same length as one that is sending sensor data?
    Analyzing a CE with the Keysight Software and a resolution of 2ms shows that its the RX time that increased so much.

    Regards Steffen