bic     $!3000,r3 / clear all bits except 9 and 10
       bic     $3000,(r1) / clear only bits 9 and 10
       rol     r3
       rol     r3
       rol     r3
       bis     r3,(r1) / or old value of bits 9 and 10 with bits 12
       	               / and 13
2:
       cmp     r2,$bufp / test to see if entire I/O queue has been
                        / scanned
       bhi    1b
       mov    (sp)+,r3
       mov    (sp)+,r2
       mov    (sp)+,r1
       rts    r0

bufaloc:
       mov    r2,-(sp) / save r2 on stack
       mov    $340,*$ps / set processor priority to 7
1:
       clr    -(sp) / vacant buffer
       mov    $bufp,r2 / bufp contains pointers to I/O queue entrys
                       / in buffer area
2:
       mov    (r2)+,r5 / move pointer to word 1 of an I/O queue entry
                       / into r5
       bit    $173000,(r5) / lock+keep+active+outstanding
       bne    3f / branch when any of bits 9,10,12,13,14,15 are set
       	         / (i.e., buffer busy)
       mov    r2,(sp) / save pointer to last non-busy buffer found
       	              / points to word 2 of I/O queue entry)
3:
       cmpb   (r5),cdev / is device in I/O queue entry same as current
                        / device
       bne    3f
       cmp    2(r5),r1 / is block number in I/O queue entry, same as
       	               / current block number
       bne    3f
       tst    (sp)+ / bump stack pointer
       br     1f / use this buffer
3:
       cmp    r2,$bufp+nbuf+nbuf
       blo    2b / go to 2b if r2 less than bufp+nbuf+nbuf (all
                 / buffers not checked)
       mov    (sp)+,r2 / once all bufs are examined move pointer to
       	               / last free block
       bne    2f / if (sp) is non zero, i.e., if a free buffer is
       	         / found branch to 2f
       jsr    r0,idle; s.wait+2 / idle if no free buffers
       br     1b
2:
       tst    (r0)+ / skip if warmed over buffer
1:
       mov    -(r2),r5 / put pointer to word 1 of I/O queue entry in r5
       movb   cdev,(r5) / put current device number in I/O queue entry
       mov    r1,2(r5) / move block number into word 2 of I/O queue