This is a continuing story from https://billgrundmann.wordpress.com/2009/03/18/sniffing-canons-ettl-protocol-2/ and previous posts.
Good news! I found out today that the drop of CLK to ground (after command message 0xb4 0x3d) before the “X” pin drops is exactly 4.00 msec. This has been measured several times. This is good as we now have a leading indicator when the flash is requested to do its job! This is sufficient time for even wireless modes. Of course I don’t really have the data of the shutter curtain positions relative to the “X” pin.
I’m working on a collective document that describes everything that I’ve found so far. This would be easier for people to look at than these piece-meal postings.