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