Subversion Repositories mips32r1

###############################################################################
# TITLE: Boot Up Code
# AUTHOR: Grant Ayers (ayers@cs.utah.edu)
# DATE: 19 July 2011
# FILENAME: boot.asm
# PROJECT: University of Utah XUM Single Core
# DESCRIPTION:
#   Initializes the global pointer and stack pointer.
#   Zeros BSS memory region and jumps to main().
#
###############################################################################


        .text
        .balign 4
        .global boot
        .ent    boot
        .set    noreorder
boot:
        la      $t0, _bss_start         # Defined in linker script
        la      $t1, _bss_end
        la      $sp, _sp
        la      $gp, _gp

$bss_clear:
        beq     $t0, $t1, $cp0_setup    # Loop until BSS is cleared
        nop
        sb      $0, 0($t0)
        j       $bss_clear
        addiu   $t0, $t0, 1

$cp0_setup:
        la      $26, $run
        mtc0    $26, $30, 0             # ErrorEPC gets address of $run
        mfc0    $26, $13, 0             # Load Cause register
        lui     $27, 0x0080             # Use "special" interrupt vector
        or      $26, $26, $27
        mtc0    $26, $13, 0             # Commit new Cause register
        mfc0    $26, $12, 0             # Load Status register
        lui     $27, 0x0fff             # Disable access to Coprocessors
        ori     $27, $27, 0x00ee        # Disable all interrupts,
        and     $26, $26, $27           #   and set kernel mode
        mtc0    $26, $12, 0             # Commit new Status register
        eret                            # Return from Reset Exception

$run:
        jal     main
        nop

$done:
        j       $done
        nop
        .end boot