#################################################################################
#   File : reset.s
#   Author : Alain Greiner
#   Date : 15/09/2010
#################################################################################
#   This is an improved boot code :
#   - It initializes the Status Register (SR)
#   - It defines the stack size  and initializes the stack pointer ($29)
#   - It initializes the interrupt vector with two ISR addresses.
#       - It configurates the ICU : IRQ_IN[0] & IRQ_IN[1] activated.
#   - It initializes the EPC register, and jumps to the main in user mode.
#################################################################################

    .section .reset,"ax",@progbits

    .extern seg_stack_base
    .extern seg_data_base
    .extern main
    .extern _interrupt_vector
    .extern _isr_tty_get_task0
    .extern _isr_timer

    .globl  reset               # makes reset an external symbol
    .ent    reset
    .align  2

reset:
    .set noreorder

# initializes stack pointer
    la      $29,    seg_stack_base
    addiu   $29,    $29,    0x4000

# initializes interrupt vector
    la      $26,    _interrupt_vector   # $26 <= interrupt_vector address
    la      $27,    _isr_timer          # $27 <= isr_timer address
    sw      $27,    0($26)              # interrupt_vector[0] <= _isr_timer
    la      $27,    _isr_tty_get_task0  # $27 <= isr_tty_get_task0 address
    sw      $27,    4($26)              # interrupt_vector[1] <= _isr_tty_get_task0

# initializes ICU
    la      $26,    seg_icu_base
    li      $27,    0x3             # IRQ_IN[0] & IRQ_IN[1] enabled
    sw      $27,    8($26)          # ICU_MASK_SET 0x3

# initializes SR register
    li      $26,    0x0000FF13      # IRQ activation
    mtc0    $26,    $12

# jump to main in user mode
    la      $26,    main
    mtc0    $26,    $14
    eret

    .end    reset
    .size   reset, .-reset

    .set reorder