1:
       bit     $22000,(r5) / check bits 10, 13 (read, waiting to read)
       	                   / of I/O queue entry
       beq     1f / branch if 10, 13 zero (i.e., not reading, or waiting
       	          / to read)
       jsr     r0,idle; s.wait+2 / if buffer is reading or writing to read,
       	                         / idle
       br      1b / till finished
1:
       bis     $101000,(r5) / set bits 9, 15 in 1st word of I/O queue
                            / (write, inhibit bits)
       clr     *$ps / clear processor status
       add     $8,r5 / r5 points to first word in data area for this
       	             / block
       rts     r0

dskwr:
       bic     $100000,*bufp / clear bit 15 of I/O queue entry at
                             / bottom of queue

ppoke:
       mov     $340,*$ps
       jsr     r0,poke
       clr     *$ps
       rts     r0
poke:
       mov     r1,-(sp)
       mov     r2,-(sp)
       mov     r3,-(sp)
       mov     $bufp+nbuf+nbuf+6,r2 / r2 points to highest priority I/O
                                    / queue pointer
1:
       mov     -(r2),r1 / r1 points to an I/O queue entry
       bit     $3000,(r1) / test bits 9 and 10 of word 1 of I/O queue
                          / entry
       beq     2f / branch to 2f if both are clear
       bit     $130000,(r1) / test bits 12, 13, and 15
       bne     2f / branch if any are set
       movb    (r1),r3 / get device id
       tstb    deverr(r3) / test for errors on this device
       beq     3f / branch if no errors
       mov     $-1,2(r1) / destroy associativity
       clrb    1(r1) / do not do I/O
       br      2f
3:
       cmpb    r3,$1 / device id = 1; device is disk
       blt     prf / device id = 0; device is drum
       bgt     ptc / device id greater than or equal to 1; device is
       	           / dec tape
       bit     $2,active / test disk busy bit
       bne     2f / branch if bit is set
       bis     $2,active / set disk busy bit
       mov     r1,rkap / rkap points to current I/O queue entry for disk
       mov     2(r1),mq / put physical block number in mq
       mov     $12.,div / divide physical block number by 12.