CC2652R: More info on LL_CHANNEL_MAP_IND PDU

Hi Rahul,

I have assigned an expert to comment on this.

Best Regards,

Jan

Hi Rafael,

Thanks for the update. The connections module of the simplelink academy tells how to set connection parameters such as min, max and timeout parameters, but not about channel selection algorithm. However, I have read the below information from the BLE stack user guide related to channel selection algorithm.

https://software-dl.ti.com/lprf/simplelink_cc26x2_latest/docs/ble5stack/ble_user_guide/html/ble-stack-5.x/channel-selection-algorithm-number-two.html

The information in the above link gives an idea on how to disable CSA 2, which is enabled by default in the stack. When CSA 2 is disabled by the user then CSA 1 will be used by default. I totally get this point. But let me recall my question again.

1) Can I completely switch off the channel map update (Both CSA 1 and CSA 2) during a connection ?. If yes please let me know how can it be done ?.

2) If I cannot turn off channel map update during a connection then is it possible to control the frequency with which master device updates the channel map with slave during a connection ?. If yes then please let me know the procedure to do the same.

Thanks for your time and help.

Regards

Rahul

Please find some additional information for your understanding.

I have conducted a test case where master is a samsung note 20 ultra mobile and slave is LAUNCHXL-CC26x2R1 launchpad. Below connection parameters were set on the slave side.

Connection Update Request Params

Parameter Update Delay (ms)                  :             2000

Requested Min Conn. Interval (ms)         :             50

Requested Max Conn. Interval (ms)         :             100

Requested Slave Latency                           :             140

Requested Conn. Timeout (ms)                :             32000

Conn. Int selected by master (ms)           :             87.5

Actual conn. Int with slave latency (ms)  :             12250

Notification interval (ms)                          :             12250

Please find the below sniffer output captured using another LAUNCHXL-CC26x2R1 running sniffle_cc26x2r.out firmware. For example, the frame 736 corresponds to connection interval as well as notification interval since both are same in this case. Ideally I would expect just empty PDU at this instant from slave if there is no actual data. But, notification data was exchanged as we have notification data. Right after this in the frame pair 738-739 channel map update happened. Again we have empty PDU exchange in the frame pair 740-741. I understood from the parent issue that this additional empty PDU is due to some handshaking procedure. However, this empty PDU exchange did not stop here. Further, If we look at the next connection event at 38.270214 sec notification data has been exchanged. Again, two more empty PDU exchanges can be observed right after this in 882-883 and 888-889 message pairs. This scenario is really uncertain because slave latency is completely ignored and it is raising lot of concerns about the products battery life. Hope this explanation gives clear idea about our concerns.Sniffer output.zip 

Rahul,

I consulted with colleagues that confirmed that you can arbitrarily send the channel map updates from a central device when requested by a peripheral - i.e., our implementation of central does not send periodic LL_CHANNEL_MAP_IND packets arbitrarily during a connection but only during its establishment.

I think that solves both questions 1) and 2), right? If you want to issue a channel map update, you can use the HCI API as shown below:

HCI_LE_SetHostChanClassificationCmd()

I also send attached a simple_central file with the API call and some of the support code - just a test, but at every disconnect it arbitrarily sends a connection map update.

As for the Android, I suspect there might be a way to configure that but a search could not return anything solid.

Hope this helps,

Rafael

2210.simple_central.c

Hi Rafael,

Thanks for the solid update. Now, I will conduct the test with two TI BLE boards and check the behavior. If it is not going to happen periodically as per your update then we would have good progress. However, I will come back with an update in a day. 

Regards

Rahul

Hi Rafael,

I have conducted the test and there is no periodic channel map update between two LAUNCHXL-CC26x2R1 launchpads as you suggested. This is really helpful to us. I have another query on this. What would be the situation during BLE interference ?. Does the central perform automatic channel mapping (which I believe Adaptive frequency hopping (AFH)) when it observes interference during a connection with peripheral ?. If yes, please let me know how to enable this in the application or is it by default enabled in the TI BLE stack ?. 

Regards

Rahul Chowdary

Hi Rafael,

Thanks for your reply and it really helps. I have one final question. Using the command HCI_EXT_PacketErrorRateCmd() on my slave I can figure out good and bad channels. From master it is possible to send this channel information using  LL_CHANNEL_MAP_IND PDU and this PDU cannot be sent from slave as per specification. Therefore, I would like to know how can I send this channel information from slave to master ?. Is there a specific PDU to send channel information from slave to master or should it involve some user logic ?.

Thanks for your reply.

Regards

Rahul

Hi Rafael,

Alright. Thanks for your support. This issue can be closed. 

Regards

Rahul Chowdary