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##################################################################

# TITLE: Boot Up Code

# AUTHOR: Steve Rhoads (rhoadss@yahoo.com)

# DATE CREATED: 1/12/02

# FILENAME: boot.asm

# PROJECT: Plasma CPU core

# COPYRIGHT: Software placed into the public domain by the author.

#    Software 'as is' without warranty.  Author liable for nothing.

# DESCRIPTION:

#    Initializes the stack pointer and jumps to main().

##################################################################

   #Reserve 512 bytes for stack

   .comm InitStack, 512

   .text

   .align 2

   .global entry

   .ent entry

entry:

   .set noreorder

   #These four instructions should be the first instructions.

   #convert.exe previously initialized $gp, .sbss_start, .bss_end, $sp

   la    $gp, _gp             #initialize global pointer

   la    $5, __bss_start      #$5 = .sbss_start

   la    $4, _end             #$2 = .bss_end

   la    $sp, InitStack+488   #initialize stack pointer

$BSS_CLEAR:

   sw    $0, 0($5)

   slt   $3, $5, $4

   bnez  $3, $BSS_CLEAR

   addiu $5, $5, 4

   jal   main

   nop

$L1:

   j $L1

   .end entry

###################################################

   #address 0x3c

   .global interrupt_service_routine

   .ent interrupt_service_routine

interrupt_service_routine:

   .set noreorder

   .set noat

   #Registers $26 and $27 are reserved for the OS

   #Save all temporary registers

   #Slots 0($29) through 12($29) reserved for saving a0-a3

   addi  $29, $29, -104  #adjust sp

   sw    $1,  16($29)    #at

   sw    $2,  20($29)    #v0

   sw    $3,  24($29)    #v1

   sw    $4,  28($29)    #a0

   sw    $5,  32($29)    #a1

   sw    $6,  36($29)    #a2

   sw    $7,  40($29)    #a3

   sw    $8,  44($29)    #t0

   sw    $9,  48($29)    #t1

   sw    $10, 52($29)    #t2

   sw    $11, 56($29)    #t3

   sw    $12, 60($29)    #t4

   sw    $13, 64($29)    #t5

   sw    $14, 68($29)    #t6

   sw    $15, 72($29)    #t7

   sw    $24, 76($29)    #t8

   sw    $25, 80($29)    #t9

   sw    $31, 84($29)    #lr

   mfc0  $26, $14        #C0_EPC=14 (Exception PC)

   addi  $26, $26, -4    #Backup one opcode

   sw    $26, 88($29)    #pc

   mfhi  $27

   sw    $27, 92($29)    #hi

   mflo  $27

   sw    $27, 96($29)    #lo

   lui   $6,  0x2000

   lw    $4,  0x20($6)   #IRQ_STATUS

   lw    $6,  0x10($6)   #IRQ_MASK

   and   $4,  $4, $6

   jal   OS_InterruptServiceRoutine

   addi  $5,  $29, 0

   #Restore all temporary registers

   lw    $1,  16($29)    #at

   lw    $2,  20($29)    #v0

   lw    $3,  24($29)    #v1

   lw    $4,  28($29)    #a0

   lw    $5,  32($29)    #a1

   lw    $6,  36($29)    #a2

   lw    $7,  40($29)    #a3

   lw    $8,  44($29)    #t0

   lw    $9,  48($29)    #t1

   lw    $10, 52($29)    #t2

   lw    $11, 56($29)    #t3

   lw    $12, 60($29)    #t4

   lw    $13, 64($29)    #t5

   lw    $14, 68($29)    #t6

   lw    $15, 72($29)    #t7

   lw    $24, 76($29)    #t8

   lw    $25, 80($29)    #t9

   lw    $31, 84($29)    #lr

   lw    $26, 88($29)    #pc

   lw    $27, 92($29)    #hi

   mthi  $27

   lw    $27, 96($29)    #lo

   mtlo  $27

   addi  $29, $29, 104   #adjust sp

isr_return:

   ori   $27, $0, 0x1    #re-enable interrupts

   jr    $26

   mtc0  $27, $12        #STATUS=1; enable interrupts

   .end interrupt_service_routine

   .set at

###################################################

   .global OS_AsmInterruptEnable

   .ent OS_AsmInterruptEnable

OS_AsmInterruptEnable:

   .set noreorder

   mfc0  $2, $12

   jr    $31

   mtc0  $4, $12            #STATUS=1; enable interrupts

   #nop

   .set reorder

   .end OS_AsmInterruptEnable

###################################################

   .global  OS_AsmInterruptInit

   .ent    OS_AsmInterruptInit

OS_AsmInterruptInit:

   .set noreorder

   #Patch interrupt vector to 0x1000003c

   la    $5, OS_AsmPatchValue

   lw    $6, 0($5)

   sw    $6, 0x3c($0)

   lw    $6, 4($5)

   sw    $6, 0x40($0)

   lw    $6, 8($5)

   sw    $6, 0x44($0)

   lw    $6, 12($5)

   jr    $31

   sw    $6, 0x48($0)

OS_AsmPatchValue:

   #Registers $26 and $27 are reserved for the OS

   #Code to place at address 0x3c

   lui   $26, 0x1000

   ori   $26, $26, 0x3c

   jr    $26

   nop

   .set reorder

   .end OS_AsmInterruptInit

###################################################

   .global   setjmp

   .ent     setjmp

setjmp:

   .set noreorder

   sw    $16, 0($4)   #s0

   sw    $17, 4($4)   #s1

   sw    $18, 8($4)   #s2

   sw    $19, 12($4)  #s3

   sw    $20, 16($4)  #s4

   sw    $21, 20($4)  #s5

   sw    $22, 24($4)  #s6

   sw    $23, 28($4)  #s7

   sw    $30, 32($4)  #s8

   sw    $28, 36($4)  #gp

   sw    $29, 40($4)  #sp

   sw    $31, 44($4)  #lr

   jr    $31

   ori   $2,  $0, 0

   .set reorder

   .end setjmp

###################################################

   .global   longjmp

   .ent     longjmp

longjmp:

   .set noreorder

   lw    $16, 0($4)   #s0

   lw    $17, 4($4)   #s1

   lw    $18, 8($4)   #s2

   lw    $19, 12($4)  #s3

   lw    $20, 16($4)  #s4

   lw    $21, 20($4)  #s5

   lw    $22, 24($4)  #s6

   lw    $23, 28($4)  #s7

   lw    $30, 32($4)  #s8

   lw    $28, 36($4)  #gp

   lw    $29, 40($4)  #sp

   lw    $31, 44($4)  #lr

   jr    $31

   ori   $2,  $5, 0

   .set reorder

   .end longjmp

###################################################

   .global   OS_AsmMult

   .ent     OS_AsmMult

OS_AsmMult:

   .set noreorder

   multu $4, $5

   mflo  $2

   mfhi  $4

   jr    $31

   sw    $4, 0($6)

   .set reorder

   .end OS_AsmMult

###################################################

   .global OS_Syscall

   .ent OS_Syscall

OS_Syscall:

   .set noreorder

   syscall 0

   jr    $31

   nop

   .set reorder

   .end OS_Syscall