##################################################################
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##################################################################
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# TITLE: Boot Up Code
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# TITLE: Boot Up Code
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# AUTHOR: Steve Rhoads (rhoadss@yahoo.com)
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# AUTHOR: Steve Rhoads (rhoadss@yahoo.com)
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# DATE CREATED: 1/12/02
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# DATE CREATED: 1/12/02
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# FILENAME: boot.asm
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# FILENAME: boot.asm
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# PROJECT: Plasma CPU core
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# PROJECT: Plasma CPU core
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# COPYRIGHT: Software placed into the public domain by the author.
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# COPYRIGHT: Software placed into the public domain by the author.
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# Software 'as is' without warranty. Author liable for nothing.
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# Software 'as is' without warranty. Author liable for nothing.
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# DESCRIPTION:
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# DESCRIPTION:
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# Initializes the stack pointer and jumps to main2().
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# Initializes the stack pointer and jumps to main2().
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##################################################################
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##################################################################
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.text
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.text
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.align 2
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.align 2
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.globl entry
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.globl entry
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.ent entry
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.ent entry
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entry:
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entry:
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.set noreorder
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.set noreorder
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#These eight instructions must be the first instructions.
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#These eight instructions must be the first instructions.
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#convert.exe will correctly initialize $gp
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#convert.exe will correctly initialize $gp
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lui $gp,0
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lui $gp,0
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ori $gp,$gp,0
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ori $gp,$gp,0
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#convert.exe will set $4=.sbss_start $5=.bss_end
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#convert.exe will set $4=.sbss_start $5=.bss_end
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lui $4,0
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lui $4,0
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ori $4,$4,0
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ori $4,$4,0
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lui $5,0
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lui $5,0
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ori $5,$5,0
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ori $5,$5,0
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lui $sp,0
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lui $sp,0
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ori $sp,$sp,0xfff0 #initialize stack pointer
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ori $sp,$sp,0xfff0 #initialize stack pointer
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$BSS_CLEAR:
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$BSS_CLEAR:
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sw $0,0($4)
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sw $0,0($4)
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slt $3,$4,$5
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slt $3,$4,$5
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bnez $3,$BSS_CLEAR
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bnez $3,$BSS_CLEAR
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addiu $4,$4,4
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addiu $4,$4,4
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jal main2
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jal main2
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nop
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nop
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$L1:
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$L1:
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j $L1
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j $L1
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#address 0x3c
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#address 0x3c
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interrupt_service_routine:
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interrupt_service_routine:
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#registers $26 and $27 are reserved for the OS
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#registers $26 and $27 are reserved for the OS
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ori $26,$0,0xffff
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ori $26,$0,0xffff
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ori $27,$0,46
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ori $27,$0,46
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sb $27,0($26) #echo out '.'
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sb $27,0($26) #echo out '.'
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#normally clear the interrupt source here
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#normally clear the interrupt source here
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#return and re-enable interrupts
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#return and re-enable interrupts
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ori $26,$0,0x1
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ori $26,$0,0x1
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mfc0 $27,$14 #C0_EPC=14
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mfc0 $27,$14 #C0_EPC=14
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jr $27
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jr $27
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mtc0 $26,$12 #STATUS=1; enable interrupts
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mtc0 $26,$12 #STATUS=1; enable interrupts
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.set reorder
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.set reorder
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.end entry
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.end entry
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###################################################
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###################################################
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.globl isr_enable
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.globl isr_enable
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.ent isr_enable
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.ent isr_enable
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isr_enable:
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isr_enable:
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.set noreorder
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.set noreorder
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jr $31
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jr $31
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mtc0 $4,$12 #STATUS=1; enable interrupts
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mtc0 $4,$12 #STATUS=1; enable interrupts
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.set reorder
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.set reorder
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.end isr_enable
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.end isr_enable
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###################################################
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###################################################
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.globl putchar
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.globl putchar
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.ent putchar
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.ent putchar
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putchar:
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putchar:
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.set noreorder
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.set noreorder
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li $5,0xffff
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li $5,0xffff
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#Uncomment to make each character on a seperate line
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#Uncomment to make each character on a seperate line
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#The VHDL simulator buffers the lines
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#The VHDL simulator buffers the lines
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# sb $4,0($5)
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# sb $4,0($5)
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# ori $4,$0,'\n'
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# ori $4,$0,'\n'
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jr $31
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jr $31
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sb $4,0($5)
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sb $4,0($5)
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.set reorder
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.set reorder
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.end putchar
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.end putchar
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###################################################
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###################################################
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.globl puts
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.globl puts
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.ent puts
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.ent puts
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puts:
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puts:
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.set noreorder
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.set noreorder
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ori $5,$0,0xffff
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ori $5,$0,0xffff
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PUTS1:
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PUTS1:
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lb $6,0($4)
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lb $6,0($4)
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beqz $6,PUTS2
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beqz $6,PUTS2
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addiu $4,$4,1
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addiu $4,$4,1
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b PUTS1
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b PUTS1
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sb $6,0($5)
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sb $6,0($5)
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PUTS2:
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PUTS2:
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jr $31
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jr $31
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ori $2,$0,0
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ori $2,$0,0
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.set reorder
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.set reorder
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.end puts
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.end puts
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