l2cap implementation with static uuid and randm channel in nrf5340

[manikandan]

hello,

i am using nrf5340 in sdk 2.4 i want to implement l2cap on our customised firmware i  need  PSM value to be received from characteristic with custom uuid but most of the example uses static value for PSM which is 0x80 is there any example or link i can refer externelly for me to test this?

NOTE: i know there is no default example is there for this so any git hub links/blog would be helpful

regards

manikandan v

[Hung Bui]

Hi Manikandan, 

I'm afraid that we don't have further material compare to what I have discussed with your in the last ticket. 

 l2cap implementation on nrf5340 

You need to dig into  central_otc and peripheral_ots samples. 

[manikandan]

yes, i have refered this examples now i can be able use l2cap but only thing i am missing is how to perfrom gatt service discovery from central after establishing a connection want to know how to make central to send a request to peripheral device to set up anl2cap channel using the specfic gatt characteristic or how can i set any custom gatt characteristic?

[Hung Bui]

Hi Manikandan, 
Have you looked at the central_otc sample ? 
In the sample, the central does service discovery (discover_func() called in connected() ) then subscribe to notification (subscribe_func () ) and then write to the ots service in otc_btn_work_fn) function. 

If you are not familiar with BLE I would suggest to get started with our sample in the SDK and our Bluetooth Academy. 

[manikandan]

Yes I have seen that but what I am not getting is why they are specifing PSM value as

#define BT_GATT_OTS_L2CAP_PSM   0x0025 in ots_l2cap.c 

[Hung Bui]

I'm not so sure why BT_GATT_OTS_L2CAP_PSM has anything to do with service discovery and sending request. 
The reason BT_GATT_OTS_L2CAP_PSM has the value 0x0025 because it's a standard PSM service in the spec and it has the value 0x0025: 
https://btprodspecificationrefs.blob.core.windows.net/assigned-numbers/Assigned%20Number%20Types/Assigned_Numbers.pdf

If you are doing custom PSM you can choose anything above 0x80.