start.s

MIPS YAMON, a famous monitor inc. source, make file and PDF manuals.

/************************************************************************
 *
 *  start.S
 *
 *  Startup code
 *
 * ######################################################################
 *
 * mips_start_of_legal_notice
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 ************************************************************************/

/************************************************************************
 *  Include files
 ************************************************************************/

#include <regdefs.h>
	
/************************************************************************
 *  Definitions
 ************************************************************************/

#ifdef EL
#define END_SWAP(addr)	(addr)
#else
#define END_SWAP(addr)  ( ((addr) & ~0x3) | (3 - ((addr) & 0x3)) )		
#endif

/* Number of cycles through delay loop */
#define DELAY		50000  
	
/************************************************************************
 *  Public variables
 ************************************************************************/

/************************************************************************
 *  Static variables
 ************************************************************************/

/************************************************************************
 *  Implementation : Static functions
 ************************************************************************/
	
/************************************************************************
 *  Implementation : Public functions
 ************************************************************************/


#ifdef __ghs__
      .section .reset
#else
      .text
#endif


/************************************************************************
 *
 *                          _start
 *  Description :
 *  -------------
 *
 *  Function linked to reset vector
 *
 *  Return values :
 *  ---------------
 *
 *  None
 *
 ************************************************************************/
	
      .globl _start
      .ent   _start
	
_start:	

      .set noreorder

      /*  Address 0xBfc00010 is reserved for boardID, so
       *  branch to 0xBfc00018 (registers on CBUS are 64
       *  bit aligned).
       */
      b	    1f		/* 0xBfc00000 */
      nop		/* 0xBfc00004 */
      nop		/* 0xBfc00008 */
      nop		/* 0xBfc0000C */
      .word 0xffffffff  /* 0xBfc00010 - illegal board if not intercepted */
      .word 0xffffffff  /* 0xBfc00014 -               expanded to 64 bit */
1:
				
      /* write 0xA5 to LED */	
      lui   t0, 0xbf00
      li    t1, 0xA5
      sb    t1, END_SWAP(0x210)(t0)
      nop

      /* Base address used in the following loop */
      lui   k0, 0xbf00

      /* Forever, write "* " followed by " *" in ASCII display */
loop :

      /* Write Asterisk (ascii 42) to ASCII display pos 0 */
      li    k1, 42
      sb    k1, END_SWAP(0x5c0)(k0)

      /* Write space (ascii 32) to ASCII display pos 1    */
      li      k1, 32
      sb    k1, END_SWAP(0x5c8)(k0)

	
      /* Delay */
      li    t0, DELAY
1:
      sub   t0, t0, 1
      bne   t0, zero, 1b
      nop

	
      /* Write space (ascii 32) to ASCII display pos 0    */
      li    k1, 32
      sb    k1, END_SWAP(0x5c0)(k0)

      /* Write Asterisk (ascii 42) to ASCII display pos 1 */
      li    k1, 42
      sb    k1, END_SWAP(0x5c8)(k0)

	
      /* Delay */
      li    t0, DELAY
1:
      sub   t0, t0, 1
      bne   t0, zero, 1b
      nop

	
      /* Loop */
      b     loop
      nop

	
      .set reorder

      .end   _start