man/man2/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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DESCRIPTION     When arg\b\b\b___ is 0,
interrupts (ASCII DELETE) are ignored.
When arg\b\b\b___ is 1,
interrupts cause their normal result, that is, force an exit\b\b\b\b____.
When arg\b\b\b___ 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\b\b\b___ 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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SEE ALSO        quit(II)
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DIAGNOSTICS     --
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BUGS            --