usr/src/sys/vax/mdec/mttoggle.s

/*
 * Copyright (c) 1980 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 */

#ifndef lint
_sccsid:.asciz  "@(#)mttoggle.s 6.2 (Berkeley) %G%"
#endif not lint

/*
 * Prototype toggle in bootstrap code for mt type tapes.
 * If on anything but a 780 with a tape at drive 0 of mba 1
 * this will have to be repaired by patching mba and mt.
 */
        movl    mba,r10
        mull3   mt,$0x80,r11
        addl3   r11,r10,r11
        addl2   $0x400,r11
        movzbl  $1,4(r10)
        movzbl  $4,8(r11)               /* drive zero, one record */
        clrl    12(r10)                 /* set address to zero */
        movl    $0x80000000,0x800(r10)  /* validate map register */
        cvtwl   $-512,16(r10)           /* set byte count */
        movzwl  $512,20(r11)            /* set byte count */
0:
        movl    0x44(r11),r0
        bbc     $15,r0,0b
        movzbl  $071,(r11)              /* read forward, go */
        halt
        .align  2
mba:    .long   0x20012000
mt:     .long   0