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               # Load the address of $run into

        mtc0    $26, $30, 0             #   the ErrorEPC

        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, 0xffff

        and     $26, $26, $27

        lui     $27, 0xffff             # Enable, but mask all interrupts

        ori     $27, $27, 0x00ff

        and     $26, $26, $27

        ori     $27, $0, 0x0001         # Base operating mode is Kernel

        or      $26, $26, $27

        mtc0    $26, $12, 0             # Commit new Status register

        #lui    $26, 0x0000             # 1ms timer (50 MHz)

        #ori    $26, $26, 0xc350

        lui     $26, 0x0007             # 10ms timer (50 MHz)

        ori     $26, $26, 0xa120

        #lui    $26, 0x004c             # 100ms timer (50 MHz)

        #ori    $26, $26, 0x4b40

        #lui    $26, 0x00be             # 250ms timer (50 MHz)

        #ori    $26, 0xbc20

        #lui    $26, 0x017d             # 500ms timer (50 MHz)

        #ori    $26, 0x7840

        #lui    $26, 0x02fa             # 1 sec timer (50 MHz)

        #ori    $26, $26, 0xf080

        mtc0    $26, $11, 0             # Set Compare register to timer value

        eret                            # Return from Reset Exception

$run:

        jal     kernel

        nop

$done:

        j       $done

        nop

        .end boot