How to receive characteristics more than 20 bytes?

[PapoKarlo]

in micropython off docs

Characteristics and descriptors have a default maximum size of 20 bytes. Anything written to them by a client will be truncated to this length. However, any local write will increase the maximum size, so if you want to allow larger writes from a client to a given characteristic, use gatts_write after registration. e.g. gatts_write(char_handle, bytes(100))

how can i send gatts_write(char_handle, bytes(100)) ?

[b3b]

This is is from another library, this project is not related to micropython.

[PapoKarlo]

im trying to connect android kivy app with your lib to ESP32 with micropython on board, then i connect directly i get limit 20 bytes. if i at same time connecting with Bluetooth Terminal (app from play market) limit got off

i think Bluetooth Terminal send some command to gatt server to insrease limit,

[b3b]

It is necessary to negotiate on the MTU value with the server device. Negotiation could be started by calling requestMTU function of the BluetoothGatt ( https://developer.android.com/reference/android/bluetooth/BluetoothGatt#requestMtu(int) ) BluetoothGatt Java object is accessible via the able.BluetoothDispatcher.gatt attribute

# ble: BluetoothDispatcher object
ble.gatt.requestMtu(103)  # Need to request 3 extra bytes for ATT packet header

# wait for the MTU response from the server ...

# Now it is possible to send 100 bytes at once
# characteristic: BluetoothGattCharacteristic Java object
ble.write_characteristic(characteristic, range(100))

There is no onMtuChanged callback in able, I think it is worth to add it. Thanks for raising this.

[b3b]

on_mtu_changed callback is added. Usage example: https://able.readthedocs.io/en/latest/#change-mtu

[PapoKarlo]

thanks, it work :)