source: rtems/c/src/lib/libbsp/mips/jmr3904/start/start.S @ b335c503

/*
 * start.S -- startup file for JMR3904 BSP based upon crt0.S from
 * newlib-1.8.2/libgloss/mips and adapted for RTEMS.
 *
 * crt0.S -- startup file for MIPS.
 *
 * Copyright (c) 1995, 1996, 1997 Cygnus Support
 *
 * The authors hereby grant permission to use, copy, modify, distribute,
 * and license this software and its documentation for any purpose, provided
 * that existing copyright notices are retained in all copies and that this
 * notice is included verbatim in any distributions. No written agreement,
 * license, or royalty fee is required for any of the authorized uses.
 * Modifications to this software may be copyrighted by their authors
 * and need not follow the licensing terms described here, provided that
 * the new terms are clearly indicated on the first page of each file where
 * they apply.
 */

#include <asm.h>
#include "regs.S"

#ifdef __mips16
/* This file contains 32 bit assembly code.  */
        .set nomips16
#endif

/* This is for referencing addresses that are not in the .sdata or
   .sbss section under embedded-pic, or before we've set up gp.  */
#ifdef __mips_embedded_pic
# ifdef __mips64
#  define LA(t,x) la t,x-PICBASE ; daddu t,s0,t
# else
#  define LA(t,x) la t,x-PICBASE ; addu t,s0,t
# endif
#else /* __mips_embedded_pic */ 
# define LA(t,x) la t,x
#endif /* __mips_embedded_pic */ 

        .text
        .align  2

/* Without the following nop, GDB thinks _start is a data variable.
 * This is probably a bug in GDB in handling a symbol that is at the
 * start of the .text section.
 */
        nop

        .globl  _start
        .ent    _start
_start:
        .set    noreorder
        # Get the address of start into $5 in a position independent fashion.
        # This lets us know whether we have been relocated or not.
        
        $LF1 = . + 8
        bal     $LF1
        nop
_branch:
        move    $5, $31                         # $5 == where are we
        li      $6, 0x8800000c                  # $6 == where we want to be
        #la      $6,_branch
        beq     $5, $6, _start_in_ram
        nop
        # relocate the code from EEPROM to RAM
        la      $7, _edata
relocate:
        lw      $8, ($5)                        # $8 = *EEPROM
        addu    $5, $5, 4                       # EEPROM++
        sw      $8, ($6)                        # *RAM = $8
        addu    $6, $6, 4                       # RAM++
        bne     $6, $7, relocate                # copied all the way to edata?
        nop
        la      $6, _start_in_ram
        jr      $6
        nop
        .end _start

        
        .globl  _start_in_ram
        .ent _start_in_ram
_start_in_ram:
        nop

#ifdef __mips_embedded_pic
        PICBASE = .+8
        bal     PICBASE
        nop
        move    s0,$31
#endif

        li      v0, SR_CU1|SR_PE|SR_FR|SR_KX|SR_SX|SR_UX
        mtc0    v0, C0_SR
        mtc0    zero, C0_CAUSE

/* Check for FPU presence */
#ifndef __mips_soft_float
/* This doesn't work if there is no FPU.  We get illegal instruction
   exceptions.  */
        li      t2,0xAAAA5555
        mtc1    t2,fp0          /* write to FPR 0 */
        mtc1    zero,fp1        /* write to FPR 1 */
        mfc1    t0,fp0
        mfc1    t1,fp1
        nop
        bne     t0,t2,1f        /* check for match */
        nop
        bne     t1,zero,1f      /* double check */
        nop
#ifndef __mips64  /* Clear the FR bit */
        li      v0, SR_CU1|SR_PE|SR_KX|SR_SX|SR_UX
        mtc0    v0, C0_SR
#endif
        j       2f
        nop
#endif
1:
        li      v0, SR_PE|SR_FR|SR_KX|SR_SX|SR_UX
        mtc0    v0, C0_SR
2:
/* Fix high bits, if any, of the PC so that exception handling 
   doesn't get confused.  */
        LA (v0, 3f)
        jr      v0
        nop
3:
        LA (gp, _gp)                            # set the global data pointer
        .end _start

/*
 * zero out the bss section.
 */
        .globl  __memsize
        .globl  zerobss
        .ent    zerobss
zerobss:
        LA (v0, _fbss)
        LA (v1, _end)
3:
        sw      zero,0(v0)
        bltu    v0,v1,3b
        addiu   v0,v0,4                         # executed in delay slot

        la      t0, _stack_init                 # initialize stack so we 
        /* We must subtract 24 bytes for the 3 8 byte arguments to main, in
           case main wants to write them back to the stack.  The caller is
           supposed to allocate stack space for parameters in registers in
           the old MIPS ABIs.  We must do this even though we aren't passing
           arguments, because main might be declared to have them. 

           Some ports need a larger alignment for the stack, so we subtract
           32, which satisifes the stack for the arguments and keeps the
           stack pointer better aligned.  */
        subu    t0,t0,32
        move    sp,t0                           # set stack pointer
        .end    zerobss

        .globl  exit .text
        .globl  init
        .ent    init
init:

        move    a0,zero                         # set argc to 0
        jal     boot_card                       # call the program start function
        nop

        # fall through to the "exit" routine
        jal     _sys_exit                       # call libc exit to run the G++
                                                # destructors
        move    a0,v0                           # pass through the exit code
        .end    init
        
/*
 * _sys_exit -- Exit from the application. Normally we cause a user trap
 *          to return to the ROM monitor for another run. NOTE: This is
 *          the only other routine we provide in the crt0.o object, since
 *          it may be tied to the "_start" routine. It also allows
 *          executables that contain a complete world to be linked with
 *          just the crt0.o object.
 */
        .globl  _sys_exit
        .ent _sys_exit
_sys_exit:
7:
#ifdef GCRT0
        jal     _mcleanup
        nop
#endif
        # break instruction can cope with 0xfffff, but GAS limits the range:
        break   1023
        nop
        b       7b                              # but loop back just in-case
        nop
        .end _sys_exit

/* EOF crt0.S */