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