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acd is composed of four procs
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wineventproc (win.c:/^wineventproc)
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reads acme window events, sends them along w->cevent.
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cdstatusproc (mmc.c:/^cdstatusproc)
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reads cd status once per second, sending
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status updates to d->cstatus.
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detects disk changes, sends new tocs to d->ctocdisp.
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cddbproc (cddb.c:/^cddbproc)
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reads tocs from d->cdbreq, if it finds
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translations in the cddb, sends new tocs to d->cdbreply.
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eventwatcher (main.c:/^eventwatcher)
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the main event loop.
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reads status from d->cstatus.
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reads events from w->cevent.
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reads new tocs to display from d->ctocdisp.
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sends new tocs to translate to d->cdbreq.
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reads new translated tocs from d->cdbreply.
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an interesting bug in the original design:
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both cdstatusproc and the eventwatcher proc
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issue scsi commands. (the eventwatcher responds to
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things such as Play, Stop, etc., as well as advancing the track.)
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the sd(3) driver did not expect overlapped commands,
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and crashed.
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this has been fixed by making the scsi(2) commands threadsafe,
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and making the sd(3) driver more robust.
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