About MTU

[xandros6]

Hi, can you give more information about auto sending multiple chunk of data with MTU=20byte?

Thanks.

[mikolak]

Hi!

What do you mean auto sending?

iOS by default tries to negotiate MTU to ~186 bytes, on Android you have to specify it manually, either by passing optional argument to peripheral.connect(), or by calling peripheral.requestMtu() after connecting.

[xandros6]

Yes ok, but if I need to send more than MTU bytes, I need to manage it manually or there is some feature of the lib that automates the sending of the chunk of bytes.

In native Android implementations there are 3 options how you can achieve it:

• You may request higher MTU from the phone using this method.
• If you are using Write With Response (write type WRITE_TYPE_DEFAULT in Android), and your device supports Long Write (that means it reserves more bytes in a buffer for each writes), you may just write longer packet despite having shorter MTU. Android will automatically chunk data into at-most-MTU-size packets and will send it to the peripheral. For you, it will be transparent. This, however, does not work with Write Without Response (WRITE_TYPE_NO_RESPONSE).
• If your device does not support higher MTUs, or you are using Write Without Response, or Long Write is not possible, you have to split your data into at most 20-bytes chunks.

[mikolak]

We're not handling it automatically and do not support long write.

peripheral.requestMtu() returns the negotiated mtu and you can use that info for splitting chunks of data.

[xandros6]

Ok, thanks!