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?

[manikandan]

Hello,

I can able to do connection with custom PSM as I have asked in my question I want to make l2cap connection with random PSM (PSM value should genrate after discovery) not custom one 

[Hung Bui]

Hi, 
Have you tried use test with fixed custom PSM ? 
Have you managed to establish a L2CAP connection with that. 
I would suggest to make sure everything is working before you test with dynamic random PSM. 

I found this in the spec: 

My understanding is that you can choose the PSM value from the initiator side. 
Try something like 0x1001.

[manikandan]

yes, i have tested with custom psm that is working fine.. but if i give value in  the range of >0x1000 i am getting unknown error while making l2cap channel connection with bt_l2cap_chan_connect .. that is where i am stuck 

[Hung Bui]

Hi Manikandan,
Could you show how exactly you assign the value ? 
I think I have confused between PSM and SPSM. It more likely that what we use as psm in our code is actually SPSM. 
You can find this : 

It's matched with the SPSM in the spec: 

So please try using psm value = 0x80, or better set it to 0 and let it dynamically assigned. 

[manikandan]

hello thanks for your reply  that is also not working my steps

1)initaiting a discovery service with static uuid ABDD3056 28FA 441D A470 55A75A52553A

2)after making ble connection initaiting a l2cap register using this register_l2cap_server

3)and making l2cap connection using bt_l2cap_ecred_chan_connect

4)and sending the data using this bt_l2cap_chan_send

but i still could not be able to mkq the l2cap connection 

regards

manikandan V

[Hung Bui]

Hi, 
I'm sorry that the issue has been dragging for so long. 
But can you clarify that even if you use BT_GATT_OTS_L2CAP_PSM 0x0025 like in ots_l2cap you still can't make it work ? 
I don't see why it worked for the OTS but not for you ? 
At which step the OTS works , but not your own l2cap channel ? 

[manikandan]

i too want to close this as soon  as possible OTS default sample working fine..my l2cap gets stuck at bt_l2cap_ecred_chan_connect getting unknown error in central

regards

manikandan v

[Hung Bui]

Hi, 
Can you step into the code and check why it didn't return. 
Could you explain why you want to do credit based L2CAP ? 
What's the limitation of the ots that you decide to make the change ? 
Have you enabled CONFIG_BT_L2CAP_ECRED=y ? 
Have you studied the sample in \zephyr\tests\bsim\bluetooth\host\l2cap ? 
I saw that they use bt_l2cap_ecred_chan_connect in credits_seg_recv and credits