V4/man/manx/intr.2

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NAME		intr  --  set interrupt handling
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SYNOPSIS	sys intr; arg  / intr = 27.
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intr(label)
int *label;
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DESCRIPTION	When arg___ is 0,
interrupts (ASCII DELETE) are ignored.
When arg___ is 1,
interrupts cause their normal result, that is, force an exit____.
When arg___ is a location within the program, control is
transferred to that location when an interrupt occurs.
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After an interrupt is caught, it is possible to resume
execution by means of an rti___ instruction; however, great
care must be exercised, since
all I/O is terminated abruptly upon an interrupt.
In particular, reads of the typewriter tend to return
with 0 characters read, thus simulating an end of file.
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From C, the interface is slightly different.
An argument of 0 or 1 has the
afore-mentioned effect of suppressing and forcing termination on
interrupts respectively.
An argument which is a label causes control
to be sent to the label when an interrupt occurs;
however the stack is set to have the same value
as it did when intr____ was called;
thus control returns to the complete execution environment
pertaining at the time of the call to intr____.
It is an error to call intr____ in a subroutine
and return from that subroutine, since
if an interrupt occurs
control will be returned
to a non-existent
environment.
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It is not possible (with the C version of this call)
to resume execution after an interrupt.
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SEE ALSO	quit(II)
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DIAGNOSTICS	--
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BUGS		--