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Annotation of xinu/sys/ctxsw.s, revision 1.1.1.1

1.1       root        1: /* ctxsw.s - ctxsw */
                      2: 
                      3: #include <procreg.h>
                      4: 
                      5: /*------------------------------------------------------------------------
                      6:  * ctxsw  --  actually perform context switch, saving/loading registers
                      7:  *------------------------------------------------------------------------
                      8:  *  Upon entry to this routine, the current stack is assumed to be the kernel
                      9:  *  stack.  The stack contains:
                     10:  * 
                     11:  *     AP+4 => address of save area with new registers, etc.
                     12:  *             Size of save area is PNREGS * sizeof (longword).
                     13:  *
                     14:  *  Assumes interrupts are disabled.
                     15:  *  See proc.h for a description of the saved state (process control block).
                     16: */
                     17:        .text
                     18:        .align  1               /* location counter lowest bit is 0     */
                     19:        .globl  _ctxsw          /* declare the routine name global      */
                     20: _ctxsw:                                /* entry point to context switch        */
                     21:        .word   0x0             /* entry mask -- save no registers      */
                     22:        movpsl  -(sp)           /* push psl                             */
                     23:        pushal  ctxswend        /* push address at which old process    */
                     24:                                /* should resume when re-started        */
                     25:        svpctx                  /* save old process' context in proctab */ 
                     26:                                /* The values to save for PC & PSL are  */
                     27:                                /* popped off the kernel stack.         */
                     28:        mtpr    4(ap), $PCBB    /* move address of new process' save    */
                     29:                                /* area to Process Control Block Base   */
                     30:        ldpctx                  /* load new process' context, push PSL  */
                     31:                                /* & PC on kernel stack.                */
                     32:        rei                     /* start executing new process          */
                     33: ctxswend:
                     34:        /* the OLD process returns here when resumed. */
                     35:        ret

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