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idiolatrie |
################################################################################
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# Start Up Code #
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#------------------------------------------------------------------------------#
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# REFERENCES #
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# #
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# [1] The MIPS programmer's handbook #
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# Erin Frquhar and Philip Bunce #
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# San Francisco, CA, Morgan Kaufmann Publishers, 1994 #
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# ISBN 1-55860-297-6 #
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# #
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#------------------------------------------------------------------------------#
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# Copyright (C)2011 Mathias Hörtnagl <mathias.hoertnagl@gmail.com> #
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# #
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# This program is free software: you can redistribute it and/or modify #
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# it under the terms of the GNU General Public License as published by #
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# the Free Software Foundation, either version 3 of the License, or #
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# (at your option) any later version. #
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# #
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# This program is distributed in the hope that it will be useful, #
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# but WITHOUT ANY WARRANTY; without even the implied warranty of #
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the #
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# GNU General Public License for more details. #
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# #
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# You should have received a copy of the GNU General Public License #
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# along with this program. If not, see <http://www.gnu.org/licenses/>. #
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################################################################################
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.ifndef STACKSIZE # Stack size in byte.
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.set STACKSIZE, 8192
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.endif
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.comm stack, STACKSIZE # Global memory: stack.
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.text
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.align 2
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################################################################################
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# Execution Start #
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#------------------------------------------------------------------------------#
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.globl start
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.ent start
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start:
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.set noreorder
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la $gp, _gp # Set global pointer.
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la $sp, stack+STACKSIZE-24 # Set stack pointer.
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la $v0, _bss_start # Global variable region start.
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la $v1, _bss_end # Global variable region end.
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clrbss: # Clear global variable region.
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sw $0, ($v0)
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addiu $v0, 4
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blt $v0, $v1, clrbss # Continue execution when .bss region is clear.
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nop
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.set noat
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and $at, $0, $0 # Clear all registers.
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.set at
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and $v0, $0, $0
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and $v1, $0, $0
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and $a0, $0, $0
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and $a1, $0, $0
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and $a2, $0, $0
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and $a3, $0, $0
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and $t0, $0, $0
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and $t1, $0, $0
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and $t2, $0, $0
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and $t3, $0, $0
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and $t4, $0, $0
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and $t5, $0, $0
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and $t6, $0, $0
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and $t7, $0, $0
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and $s0, $0, $0
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and $s1, $0, $0
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and $s2, $0, $0
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and $s3, $0, $0
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and $s4, $0, $0
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and $s5, $0, $0
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and $s6, $0, $0
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and $s7, $0, $0
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and $t8, $0, $0
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and $t9, $0, $0
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and $k0, $0, $0
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and $k1, $0, $0
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and $fp, $0, $0
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and $ra, $0, $0
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jal main # Start execution of the C main procedure.
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nop
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loop: # Final loop. Afer returning from C main loop.
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nop
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j loop # Real Infinity.
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nop
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nop
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.set reorder
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.end start
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################################################################################
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# Interrupt Start #
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#------------------------------------------------------------------------------#
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.ent intr_handler
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intr_handler:
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.set noreorder
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.set noat
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# If we do not include the Interrupt API, simply return to normal execution
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# immediately.
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.ifdef _INTERRUPT
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addiu $sp, $sp, -72 # Allocate space for all relevant registers.
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sw $at, 4($sp) # Save all registers, that are used directily
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sw $v0, 8($sp) # after a successful execution of the interrupt
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sw $v1, 12($sp) # service routines.
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sw $a0, 16($sp) # Registers $s0 - $s8 do not need to be saved,
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sw $a1, 20($sp) # since the compiler stores them if they are
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sw $a2, 24($sp) # used in a procedure.
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sw $a3, 28($sp) # $gp is the same for the entire source code.
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sw $t0, 32($sp) # Registers $k0 and $k1 are reserved for ASM
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sw $t1, 36($sp) # routines. The C compiler does not use them.
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sw $t2, 40($sp)
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sw $t3, 44($sp)
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sw $t4, 48($sp)
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sw $t5, 52($sp)
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sw $t6, 56($sp)
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sw $t7, 60($sp)
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sw $t8, 64($sp)
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sw $t9, 68($sp)
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sw $ra, 72($sp)
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mfc0 $k0, $13 # Retrieve CAUSE (Pending Interrupts).
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nop
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mfc0 $k1, $12 # Retrieve SR (Interrupt mask and global IE).
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nop
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and $k0, $k0, $k1 # Get legal pending interrupts.
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addiu $sp, $sp, -24 # Allocate minimal procedure context.
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jal intr_dispatch # Jump to C interrupt dispatch routine.
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srl $a0, $k0, 8 # a0 <- legal pending interrupts.
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addiu $sp, $sp, 24 # Deallocate minimal procedure context.
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lw $at, 4($sp) # Restore saved registers.
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lw $v0, 8($sp)
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lw $v1, 12($sp)
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lw $a0, 16($sp)
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lw $a1, 20($sp)
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lw $a2, 24($sp)
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lw $a3, 28($sp)
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lw $t0, 32($sp)
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lw $t1, 36($sp)
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lw $t2, 40($sp)
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lw $t3, 44($sp)
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lw $t4, 48($sp)
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lw $t5, 52($sp)
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lw $t6, 56($sp)
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lw $t7, 60($sp)
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lw $t8, 64($sp)
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lw $t9, 68($sp)
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lw $ra, 72($sp)
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addiu $sp, $sp, 72 # Undo stack allocation.
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.endif
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mfc0 $k1, $14 # Retrieve EPC.
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nop
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jr $k1 # Return to normal execution.
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rfe # Restore from exception. Pop IE stack.
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.set at
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.set reorder
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.end intr_handler
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################################################################################
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# Return to Bootloader #
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#------------------------------------------------------------------------------#
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.globl boot
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.ent boot
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boot:
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.set noreorder
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jr $0
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nop
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.set reorder
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.end boot
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