start.S

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/* start.S - start, bzero */

#include <armv7a.h>

/*------------------------------------------------------------------------
 * start  -  Initial entry point for a Xinu image (ARM)
 *------------------------------------------------------------------------
 */
   .text
   .globl  start           /* Declare entry point global   */

start:
   /* Load the stack pointer with end of memory */

   ldr sp, =MAXADDR

   /* Enable the Instruction Cache */

   mrc p15, 0, r0, c1, c0, 0
   orr r0, r0, #ARMV7A_C1CTL_I
   mcr p15, 0, r0, c1, c0, 0

   /* Use bzero (below) to zero out the BSS area */

   ldr r0, =edata
   ldr r1, =end
   bl  bzero

   /* Call nulluser to initialize the Xinu system  */
   /*    (Note: the call never returns)        */

   bl  nulluser

   /* Function to zero memory (r0 is lowest addr; r1 is highest)   */

bzero:
   mov r2, #0          /* Round address to multiple    */
   add r0, r0, #3      /*   of four by adding 3 and    */
   and r0, r0, #0xFFFFFFFC /*   taking the result module 4 */
bloop: cmp r0, r1          /* Loop until last address  */
   bhs bexit           /*   has been reached       */
   str r2, [r0]        /* Zero four-byte word of memory*/
   add r0, r0, #4      /* Move to next word        */
   b   bloop           /* Continue to iterate      */
bexit: mov pc, lr          /* Return to caller     */