BLE Long write

[darren]

My Setup: Nordic is the Server, Android is the client.

I have read many, many forum posts about doing long reads/writes. Virtually everyone says you cannot do long writes. Instead you have to do a sequence of 20 byte writes.
devzone.nordicsemi.com/.../

I've also looked into Android API, and found that they do long read under the hood but do not support long write. I can only send 20 byte at a time. This is just what the forum posts have said.

HOWEVER, what I don't understand is how Noric Master Control Panel successfully executes long write. I can load up a 50 byte message and pass it over the Android App version of MCP. Is there something utilized in the MCP that I have missed, or cannot get access to in Android?

I cannot believe there is no way to write large streams of data from a phone to a BLE chip. It must be that I've missed something.

Thanks for your help!

[shibshab]

Have you seen the link layer packets that the MCP app generates when it sends the 50 byte message?

Could it be that it divides the message into smaller packets without you noticing?

[darren]

To be fair, I only have access to the Android side, but i do know there is prepareReliableWrite() type methods in android: link. Perhaps this is what is going on. I will go see if I can implement something with this.

Why is there not a longer write to be able to do data dumps? Is this a design decision of BLE?

[Matthias]

Darren, I tried to test the MCP long write while sniffing with the PCA10000, but my custom device crashes with messages greater than 20 bytes. Could you tell me the service you have tested it with?

[shibshab]

20 bytes is the limit of data packets in BLE 4.0 specification yes.

[Matthias]

That is true. But long write is a concept where the splitting and reassembly is handled by the api. Sorry, I converted this comment to an answer by mistake. It is a pitty there is no mobile Support for this site :(