Is CONFIG_BT_SMP mandatory if CONFIG_BT=y ?

[kfcube]

Hi,

I have several questions:

1. Is CONFIG_BP_SMP mandatory if CONFIG_BT=y?  If I don't need pair devices, can I disable it? If I disable it, what consequences could have?

2. If CONFIG_BP_SMP=y, will it increase the notification packet size?

The reason I am asking is I found the CONFIG_BT_L2CAP_TX_MTU will become 65 once CONFIG_BP_SMP=y. By default its 23.

3. How to calculate CONFIG_BT_L2CAP_TX_MTU? I need to notify 24 bytes data 100 times per second. With this load, how to calculate the following three configurations:

CONFIG_BT_L2CAP_TX_BUF_COUNT=10
CONFIG_BT_BUF_ACL_TX_SIZE=39
CONFIG_BT_CTLR_DATA_LENGTH_MAX=39

Thanks,

[Kazi Afroza Sultana]

Hello,

CONFIG_BT_SMP enables support for the Security Manager Protocol (SMP), so you can pair devices over LE. You can disable this configuration of you do not need to peer the device. 

Usually, controller packet size needs to be 7 bytes larger than the amount of data we want to send for keeping place for a 4-byte L2CAP header and a 3-byte ATT header. This is the reason the BLE data length is 27, and the payload size is 20 bytes. 

So, in order to notify 24 bytes , the length of CTRL DATA LENGTH should be 31. 

[kfcube]

Got it. Thanks Kazi. You have a great day!