MTU Exchange sub-procedure on s130_1.0.0

[Aymen Rejeb]

Hello Nordic Team,

As I'm worrying about the max payload lengh that I can notify using soft device s130.1.0.0 on nrf51822 (256 Kb Flash/ 16KB RAM, SDK10), I thought about the MAX ATT_MTU that we can use.

Actually after take a look on SoftDevice Specification S130 SoftDevice v2.0 document, I can see that the Exchange MTU sub-procedure (BLUETOOTH SPECIFICATION Version 4.2 [Vol 3, Part G] section 4.3.1) is not implemented by the s130 stack which mean that the default ATT_MTU (23 bytes) is used.

Also, as mentioned in (BLUETOOTH SPECIFICATION Version 4.2 [Vol 3, Part G] section 4.10.1), notifications sub-procedure does not support the long characteristic values notion! which mean that using notifications we can only notify 20 bytes (ATT_MTU-3) at a time!

Am I right ? or there is an other way to send more than 20 bytes using the notifications sub-procedure (sd_ble_gatts_hvx) using s130_1.0.0 on nRF51822 ?

Many thanks in advance,

Ayman.

[run_ar]

Long ATT MTU exchange was introduced in S132 v3. So this feature is not supported on the nR51 series. This means you have to use a 20 byte characteristic, divide the data into 20 byte chuncks and then combine them again on the receiving end. If you need longer than 20 byte attributes you can use the read/write long procedures.

[Aymen Rejeb]

Thanks a lot :)