Undestanding BOSSAC's SAM-BA protocol implementation

[theyd]

Hi,

I have to implement the SAM-BA protocol to flash an ATSAMD21 by another embedded system. In order to do that i would like to extract the essence of BOSSA to build a minimal version of it.

Additionally i would like to understand the SAM-BA protocol, i don't like "blind-copying" :)

What i found is this: https://sourceforge.net/p/lejos/wiki-nxt/SAM-BA%20Protocol/

Reading the sourcecode of BOSSA i noticed that it reads a file bytewise and writes it in the Flasher::write(..) method, which basically calls Flash::loadBuffer(..) and Flash::writeBuffer(..) in sequence.

Digging deeper into the code you can see that loadBuffer results in sending S<address><size># and writeBuffer results in sending Y<address>,0#

My questions regarding to this are:

1. What does the "Y" command do? In the document above there is only the "S" command described
2. Is there an official specification of that protocol?

Thank you for your help!