What turns on the 'working' icon on PC7300?

[Bill Mayhew]

Hi,

Does anybody know what situations cause [apparently] the kernel to
display the working icon on the console terminal.  Casual
observation seems to indicate that that the icon is displayed
whenever the foreground task of the console process group has not
been in keyboard wait for mote than about 500 mS.

I noticed that when I run a P/D basic interpreter that I compiled
on the 3b1 assuming only generic Sys V, that the working icon is
off while basic is in immediate mode.  The icon pops up about 1/2
second after RUN has been invoked.  Basic is nothing more than a
big C program -- no assembly language subroutines, etc.  Looks like
scanf keeps the icon turned off, while beginning RUN allows the
icon to pop back up.

I don't have anything special in mind for the working icon; I'd
just like to know more about what it is really telling me about
what is going on.  I am a bit curious about the CPU overhead eaten
by the icon; it would seem that the kernel must have to keep
looking at the process table to see if the task is blocked waiting
for input .. or is it implemented as part of the console tty
driver?...

Bill
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