tbillion:
i cobbled this together from online examples it works to an extent, but not well enough :
Why did you modify Robin's recvWithStartEndMarkers code?
I guess this is the problem:
Your parser sets commands[6]. The initial value of commands[6] is 0; this is not 87 and hence the parser will never be called from showNewData().
BTW, with a 1024 char buffer and a 200 byte buffer you're getting close to the limits of a 328 based board (Uno, Nano, ...); which board are you using?