Andy pointed me to this problem on the forum:
https://forum.linuxcnc.org/forum/38-general-linuxcnc-questions/30276-run-from-line-and-v-2-7-3
Thanks for the heads-up, Andy, and thanks to Paul for providing enough
information to figure out what's happening. Here's the forensics
report, which points to a bug.
When the operator sets a start line and runs the program, task runs the
interpreter through the g-code file as usual, generating canonical
commands and queueing those up on the NML_INTERP_LIST. But once the
start line is reached, the list is cleared, and those commands are never
issued. After the start line, execution continues as usual. This
breaks when the interpreter reaches a queue buster before the start line.
In general, when the interpreter hits a queue buster, it can't go any
further because it can't know the machine state following the code. So,
task issues any commands queued up in the NML_INTERP_LIST, and once the
queue buster finishes, its result is known and the interpreter can
continue on.
In the case of the start line, a queue buster prior to the start will
still trigger this behavior. In Paul's case, the G38.1 forced task to
clear the queue, issuing all codes in the interp list, causing the
behavior he reported.
Unfortunately, there's no trivial fix to make this work properly. It's
pretty easy to see how a probe operation's result can't be predicted
without actually running it, and the interpreter can't know whether the
codes after Paul's start line will be affected by the earlier probe.
The proper fix may be to throw an error if a queue buster is encountered
before any start line, and let the operator decide what to do.
As for Paul's question about downgrading, this isn't a regression in
LinuxCNC. His previous successful use of the start line must not have
followed a queue buster.
John
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