tests/functional: fix MCS-51 idle wakeup race - #37
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The MCS-51 ISA functional test starts Timer 0 immediately before entering idle. If the host is descheduled long enough, the timer can expire and its handler can stop it before PCON.IDL executes. The firmware then enters idle with no remaining wake source and Meson eventually times out. Keep Timer 0 running in the handler and stop it only after IDL returns. Remove the 180-second timeout workaround because the failures were hangs rather than slow test runs. Signed-off-by: Chao Liu <chao.liu@processmission.com>
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Summary
PCON.IDL.Root cause
The reported CI job did not run slowly; it hung. The idle firmware starts Timer 0 immediately before entering idle. If the runner is descheduled long enough, Timer 0 can overflow first, and the interrupt handler stops it before
PCON.IDLexecutes. The firmware then enters idle with no remaining wake source, so the console wait lasts until Meson kills the test.A deterministic icount fault injection forced Timer 0 to expire before the idle instruction. Before this change it timed out in 5/5 runs. The trace showed the interrupt being taken and returned before
PCON.IDL, with no active timer left. Keeping Timer 0 active in the handler let a later overflow wake the CPU; the same fault injection then passed in 5/5 runs.Validation
ninja -C builds/build-mcs51-ci-flakepython3 -m py_compile tests/functional/mcs51/test_isa.pyscripts/checkpatch.pl --no-strict origin/devel..HEAD(0 errors, 0 warnings)