Enable >20 bytes on BLE

[microbuilder]

By default, BLE and the nRF52 are limited to transmitting 20 bytes per packet, but there is a mechanism to transfer more data for higher throughput on supporting devices (on both ends of the connection).

An optional command should be added to the Bluefruit class to enable extended packets.

See the following thread for details: https://devzone.nordicsemi.com/question/95745/what-is-the-max-data-throughput-with-s132-v3/?answer=95750#post-id-95750

This should allow up to 244 bytes per transfer.

[hathach]

SD132 v3.0.0 is required for negotiating MTU. Currently we only have S132 v2.0.1 with legacy bootloader

[microbuilder]

Deferring this to a future release where we can update to the secure bootloader at the same time. 20 bytes per packet still gives about 4KB/s from local testing, which is better than the nRF51, and is consistent with user expectations.

[microbuilder]

Bluefruit52 Throughput Example
Connected
Connected. Send a key and press enter to start test
Sending 61440 bytes ...
Sent 61440 bytes in 15.66 seconds.
Speed 
3.92 KB/s.

Connected. Send a key and press enter to start test

This is sending 60 bytes packets, just to have an idea of throughput. ~4KB/s is pretty decent for BLE UART (sending to Bluefruit LE Connect on OS X 10.11.6 in this case).

[TauqirH]

@hathach , was this feature ever implemented ? I think it's still 20 bytes.

[vChavezB]

was this problem solved ?

nvm. seems I forgot to add before bluefruit.begin() the call

Bluefruit.configPrphBandwidth(BANDWIDTH_MAX);

also the characteristic must be changed with

setMaxLen before begin()