# SPIM S20 MIPS simulator.
# The default trap handler for spim.
#
# Copyright (C) 1990-2003 James Larus, larus@cs.wisc.edu.
# ALL RIGHTS RESERVED.
#
# SPIM is distributed under the following conditions:
#
# You may make copies of SPIM for your own use and modify those copies.
#
# All copies of SPIM must retain my name and copyright notice.
#
# You may not sell SPIM or distributed SPIM in conjunction with a commerical
# product or service without the expressed written consent of James Larus.
#
# THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
# PURPOSE.
#

# $Header: $


# Define the exception handling code.  This must go first!

	.kdata
__m1_:	.asciiz "  Exception "
__m2_:	.asciiz " occurred and ignored\n"
__e0_:	.asciiz "  [Interrupt] "
__e1_:	.asciiz	""
__e2_:	.asciiz	""
__e3_:	.asciiz	""
__e4_:	.asciiz	"  [Unaligned address in inst/data fetch] "
__e5_:	.asciiz	"  [Unaligned address in store] "
__e6_:	.asciiz	"  [Bad address in text read] "
__e7_:	.asciiz	"  [Bad address in data/stack read] "
__e8_:	.asciiz	"  [Error in syscall] "
__e9_:	.asciiz	"  [Breakpoint] "
__e10_:	.asciiz	"  [Reserved instruction] "
__e11_:	.asciiz	""
__e12_:	.asciiz	"  [Arithmetic overflow] "
__e13_:	.asciiz	"  [Inexact floating point result] "
__e14_:	.asciiz	"  [Invalid floating point result] "
__e15_:	.asciiz	"  [Divide by 0] "
__e16_:	.asciiz	"  [Floating point overflow] "
__e17_:	.asciiz	"  [Floating point underflow] "
__excp:	.word __e0_,__e1_,__e2_,__e3_,__e4_,__e5_,__e6_,__e7_,__e8_,__e9_
	.word __e10_,__e11_,__e12_,__e13_,__e14_,__e15_,__e16_,__e17_
s1:	.word 0
s2:	.word 0

# This is the exception handler code that the processor runs when
# an exception occurs. It only prints some information about the
# exception, but scan server as a model of how to write a handler.
#
# Because we are running in the kernel, we can use $k0/$k1 without
# saving their old values.
	.ktext 0x80000080
	.set noat
	move $k1 $at		# Save $at
	.set at
	sw $v0 s1		# Not re-entrent and we can't trust $sp
	sw $a0 s2		# But, we need to use these registers

	mfc0 $k0 $13		# Cause register
        srl $a0 $k0 2		# Extract ExcCode Field
	andi $a0 $a0 0xf

        blez $a0 int_ret	# Don't print interrupts
        nop

	# Print information about exception.
	#
	li $v0 4		# syscall 4 (print_str)
	la $a0 __m1_
	syscall

	li $v0 1		# syscall 1 (print_int)
        srl $a0 $k0 2		# Extract ExcCode Field
	andi $a0 $a0 0xf
	syscall

	li $v0 4		# syscall 4 (print_str)
	lw $a0 __excp($k0)
	syscall

	bne $k0 0x18 ok_pc	# Bad PC exception requires special checks
        nop

	mfc0 $a0, $14		# EPC
	andi $a0, $a0, 0x3	# Is EPC word-aligned?
	beq $a0, 0, ok_pc
        nop

	li $v0 10		# Exit on really bad PC
	syscall

ok_pc:
	li $v0 4		# syscall 4 (print_str)
	la $a0 __m2_
	syscall

	mtc0 $0, $13		# Clear Cause register

# Return from exception. Skip offending
# instruction to avoid infinite loop.
#
ret:	lw $v0 s1		# Restore regs
	lw $a0 s2
	mfc0 $k0 $14		# EPC
	addiu $k0 $k0 4		# Return to next instruction
	.set noat
	move $at $k1		# Restore $at
	.set at
	rfe			# Return from exception handler
	jr $k0
        nop

# Return from interrupt. Don't skip instruction
# since it has not executed.
#
int_ret:lw $v0 s1		# Restore regs
	lw $a0 s2
	mfc0 $k0 $14		# EPC (return to EPC)
	.set noat
	move $at $k1		# Restore $at
	.set at
	rfe			# Return from exception handler
	jr $k0
        nop


# Standard startup code.  Invoke the routine "main" with arguments:
#	main(argc, argv, envp)
#
	.text
	.globl __start
__start:
	lw $a0, 0($sp)		# argc
	addiu $a1, $sp, 4	# argv
	addiu $a2, $a1, 4	# envp
	sll $v0, $a0, 2
	addu $a2, $a2, $v0
	jal main
        nop

	li $v0 10
	syscall			# syscall 10 (exit)

	.globl __eoth
__eoth: