jsr     r0,swap / swap out process that needs to sleep
       mov     (sp)+,cdev / restore device
       jsr     r0,isintr / check for interrupt of new process
               br      2f / yes, return to new user
       movb    (sp)+,r1 / no, r1 = old process number that was originally
                        / on the wait channel
       beq     1f / if 0 branch
       mov     $runq+4,r2 / r2 points to lowest priority queue
       mov     $300,*$ps / processor priority = 6
       jsr     r0,putlu / create link to old process number
       clr     *$ps / clear the status; process priority = 0
1:
       rts     r0 / return
2:
       jmp     sysret / return to user

isintr:
       mov     r1,-(sp) / put number of wait channel on the stack
       mov     r2,-(sp) / save r2
       mov     u.ttyp,r1 / r1 = pointer to buffer of process control
                         / typewriter
       beq     1f / if 0, do nothing except skip return
       movb    6(r1),r1 / put interrupt char in the tty buffer in r1
       beq     1f / if its 0 do nothing except skip return
       cmp     r1,$177 / is interrupt char = delete?
       bne     3f / no, so it must be a quit (fs)
       tst     u.intr / yes, value of u.intr determines handling
                      / of interrupts
       bne     2f / if not 0, 2f. If zero do nothing.
1:
       tst     (r0)+ / bump r0 past system return (skip)
4:
       mov     (sp)+,r2 / restore r1 and r2
       mov     (sp)+,r1
       rts     r0
3: / interrupt char = quit (fs)
       tst     u.quit / value of u.quit determines handling of quits
       beq     1b / u.quit = 0 means do nothing
2: / get here because either u.intr <> 0 or u.qult <> O
       mov     $tty+6,r1 / move pointer to tty block into r1
1: / find process control tty entry in tty block
       cmp     (r1),u.ttyp / is this the process control tty buffer?
       beq     1f / block found go to 1f
       add     $8,r1 / look at next tty block
       cmp     r1,$tty+[ntty*8]+6 / are we at end of tty blocks
       blo     1b / no
       br      4b / no process control tty found so go to 4b
1:
       mov     $240,*$ps / set processor priority to 5
       movb    -3(r1),0f / load getc call argument; character llst
                          / identifier
       inc     0f / increment
1:
       jsr     r0,getc; 0:.. / erase output char list for control
               br 4b / process tty. This prevents a line of stuff
                     / being typed out after you hit the interrupt