Max MTU size for BLE (NRF51 series)

[Chocol8]

Hello,

I do know that it is a lot of information here in dev zone about this topic but I need a confirmation from a Nordic employee. We had a disscusion at workplace wheter it is possibile to send packets which size exceeds 20B for user using nrf51822 or nrf51422 while using one of it's stacks e.g. s110 or s130? I do not see that this would be possibile. Moreover, I was offered to use s132 which supports up to 512B MTU. I have tried to search why this stack can not be used with NRF51 unfortunately I could not find any information about this. I do know that they are incompatible. Could you, please, explain this? 

Best regards

[Håkon Alseth]

Hello,

 

The MTU_SIZE is changed based on a negotiation between the master and slave device (ATT Exchange MTU Request/Response), where the lowest value is chosen. If the master can do 158 bytes, and the slave can do 23 bytes, 23 bytes will be chosen for this link.

The Softdevices for nRF51-series devices, S110/S120/S130, supports a MTU_SIZE of 23, which limits the user data to 20 bytes.

This is documented in this section, under "ATT Features"

Best regards,

Håkon

[Chocol8]

 In addition to this, I would like to ask: is there a way to send a packet larger than 23 B MTU using NRF51 series?