Shortest preamble of a packet, nRF51 can receive.

[Chinook]

What is a minimal length of preamble, such that nRF51 is able to safely receive a packet with? Can it be made (via some magic registers) to be as small as 4 bits? Then it would be possible to implement software support for classic Bluetooth on nRF51 chip. Of course all that pretty hardware for packet encoding/decoding etc would be useless, but anyway it would be a nice possibility.

[Matthias Ringwald]

Thanks a lot for the detailed answer and sharing the nifty trick of using part of the sync word to "create" an 8-bit preamble! The 'treat data with high RSSI as connect response' is a clever hack as well!

I didn't see something related to a 4-bit preamble in the latest nRF52840 SoC either :(

How long did it take to get this to work? Would you share your test code?

[Chinook]

Thanks for your interest.

I can't now say how long it took to get it work, perhaps two weeks. Sure it won't take you much if you are familiar with the corresponding part(s) of the Bluetooth spec and do everything right from the first attempt. That's not my case :). Concerning code I wouldn't publish it in its current form but I may send it to you via email, just give me your email address in a private message. Nevertheless I have to forewarn you the code was intended for testing only and is ugly, contains no comments, contains some C++ metaprogramming templates and assembly. You will have to struggle through it keeping Bluetooth spec in one hand, nRF51 reference in another, and the Cortex-M0 reference in the third. Feel free to ask if you are in a dead end.