Just after I spent 30 minutes documenting the crashing problem here, the following baffling sequence occurred. It is mindblowing that TinyG would repeatedly think Z0 was an arc command, over and over. Then it had a complete meltdown. Note at the bottom, when I manually enter a "G0Z0", and TinyG responded by sending my cutter to x5y11 at high speed, breaking the bit! WTF?
I was wrong about the problem being related to cancelling CoolTerm. What follows is all manually typed. I am not sending a file, and I didn't cancel anything.
tinyg [mm] ok>
z5
tinyg [mm] err: Arc specification error: z5
tinyg [mm] ok>
z5
tinyg [mm] err: Arc specification error: z5
tinyg [mm] ok>
Z5
tinyg [mm] err: Arc specification error: Z5
tinyg [mm] ok>
g0z0
tinyg [mm] ok>
tinyg [mm] ok>
posx:-8.905,posy:-9.592,vel:0.277,stat:5
posx:-8.760,posy:-9.374,vel:179.823
posx:-7.829,posy:-7.972,vel:691.362
posx:-5.575,posy:-4.580,vel:1242.308
posx:-2.458,posy:0.111,vel:1462.507
posx:0.773,posy:4.974,vel:1350.714
posx:3.370,posy:8.883,vel:906.929
posx:4.688,posy:10.867,vel:310.353
posx:4.994,posy:11.328,vel:22.401
posx:5.000,posy:11.336,vel:0.000,stat:3`