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.global main // int main(void)
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.global _etext // -> .data initial values in ROM
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.global _data // -> .data area in RAM
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.global _edata // end of .data area
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.global __bss_start // -> .bss area in RAM
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.global __bss_end__ // end of .bss area
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.global _stack // top of stack
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// Stack Sizes
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.set UND_STACK_SIZE, 0x00000004
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.set ABT_STACK_SIZE, 0x00000004
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.set FIQ_STACK_SIZE, 0x00000004
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.set IRQ_STACK_SIZE, 0X00000080
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.set SVC_STACK_SIZE, 0x00000004
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// Standard definitions of Mode bits and Interrupt (I & F) flags in PSRs
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.set MODE_USR, 0x10 // User Mode
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.set MODE_FIQ, 0x11 // FIQ Mode
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.set MODE_IRQ, 0x12 // IRQ Mode
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.set MODE_SVC, 0x13 // Supervisor Mode
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.set MODE_ABT, 0x17 // Abort Mode
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.set MODE_UND, 0x1B // Undefined Mode
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.set MODE_SYS, 0x1F // System Mode
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.equ I_BIT, 0x80 // when I bit is set, IRQ is disabled
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.equ F_BIT, 0x40 // when F bit is set, FIQ is disabled
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.text
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.code 32
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.align 2
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.global _boot
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.func _boot
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_boot:
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// Runtime Interrupt Vectors
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// -------------------------
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Vectors:
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b _start // reset - _start
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ldr pc,_undf // undefined - _undf
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ldr pc,_swi // SWI - _swi
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ldr pc,_pabt // program abort - _pabt
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ldr pc,_dabt // data abort - _dabt
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nop // reserved
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ldr pc,[pc,#-0xFF0] // IRQ - read the VIC
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ldr pc,_fiq // FIQ - _fiq
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#if 0
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// Use this group for production
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_undf: .word _reset // undefined - _reset
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_swi: .word _reset // SWI - _reset
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_pabt: .word _reset // program abort - _reset
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_dabt: .word _reset // data abort - _reset
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_irq: .word _reset // IRQ - _reset
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_fiq: .word _reset // FIQ - _reset
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#else
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// Use this group for development
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_undf: .word __undf // undefined
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_swi: .word __swi // SWI
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_pabt: .word __pabt // program abort
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_dabt: .word __dabt // data abort
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_irq: .word __irq // IRQ
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_fiq: .word __fiq // FIQ
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__undf: b . // undefined
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__swi: b . // SWI
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__pabt: b . // program abort
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__dabt: b . // data abort
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__irq: b . // IRQ
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__fiq: b . // FIQ
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#endif
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.size _boot, . - _boot
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.endfunc
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// Setup the operating mode & stack.
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// ---------------------------------
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.global _start, start, _mainCRTStartup
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.func _start
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_start:
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start:
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_mainCRTStartup:
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// Initialize Interrupt System
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// - Set stack location for each mode
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// - Leave in System Mode with Interrupts Disabled
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// -----------------------------------------------
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ldr r0,=_stack
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msr CPSR_c,#MODE_UND|I_BIT|F_BIT // Undefined Instruction Mode
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mov sp,r0
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sub r0,r0,#UND_STACK_SIZE
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msr CPSR_c,#MODE_ABT|I_BIT|F_BIT // Abort Mode
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mov sp,r0
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sub r0,r0,#ABT_STACK_SIZE
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msr CPSR_c,#MODE_FIQ|I_BIT|F_BIT // FIQ Mode
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mov sp,r0
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sub r0,r0,#FIQ_STACK_SIZE
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msr CPSR_c,#MODE_IRQ|I_BIT|F_BIT // IRQ Mode
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mov sp,r0
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sub r0,r0,#IRQ_STACK_SIZE
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msr CPSR_c,#MODE_SVC|I_BIT|F_BIT // Supervisor Mode
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mov sp,r0
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sub r0,r0,#SVC_STACK_SIZE
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msr CPSR_c,#MODE_SYS|I_BIT|F_BIT // System Mode
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mov sp,r0
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// Copy initialized data to its execution address in RAM
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// -----------------------------------------------------
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#ifdef ROM_RUN
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ldr r1,=_etext // -> ROM data start
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ldr r2,=_data // -> data start
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ldr r3,=_edata // -> end of data
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1: cmp r2,r3 // check if data to move
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ldrlo r0,[r1],#4 // copy it
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strlo r0,[r2],#4
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blo 1b // loop until done
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#endif
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// Clear .bss
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// ----------
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mov r0,#0 // get a zero
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ldr r1,=__bss_start // -> bss start
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ldr r2,=__bss_end__ // -> bss end
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2: cmp r1,r2 // check if data to clear
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strlo r0,[r1],#4 // clear 4 bytes
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blo 2b // loop until done
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/*
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Call C++ constructors (for objects in "global scope")
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ctor loop added by Martin Thomas 4/2005
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based on a Anglia Design example-application for ST ARM
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*/
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LDR r0, =__ctors_start__
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LDR r1, =__ctors_end__
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ctor_loop:
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CMP r0, r1
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BEQ ctor_end
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LDR r2, [r0], #4
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STMFD sp!, {r0-r1}
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MOV lr, pc
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MOV pc, r2
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LDMFD sp!, {r0-r1}
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B ctor_loop
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ctor_end:
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// Call main program: main(0)
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// --------------------------
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mov r0,#0 // no arguments (argc = 0)
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mov r1,r0
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mov r2,r0
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mov fp,r0 // null frame pointer
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mov r7,r0 // null frame pointer for thumb
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ldr r10,=main
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mov lr,pc
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bx r10 // enter main()
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/* "global object"-dtors are never called and it should not be
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needed since there is no OS to exit to. */
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.size _start, . - _start
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.endfunc
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.global _reset, reset, exit, abort
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.func _reset
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_reset:
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reset:
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exit:
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abort:
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#if 0
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// Disable interrupts, then force a hardware reset by driving P23 low
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// -------------------------------------------------------------------
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mrs r0,cpsr // get PSR
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orr r0,r0,#I_BIT|F_BIT // disable IRQ and FIQ
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msr cpsr,r0 // set up status register
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ldr r1,=(PS_BASE) // PS Base Address
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ldr r0,=(PS_PIO) // PIO Module
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str r0,[r1,#PS_PCER_OFF] // enable its clock
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ldr r1,=(PIO_BASE) // PIO Base Address
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ldr r0,=(1<<23) // P23
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str r0,[r1,#PIO_PER_OFF] // make sure pin is contolled by PIO
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str r0,[r1,#PIO_CODR_OFF] // set the pin low
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str r0,[r1,#PIO_OER_OFF] // make it an output
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#endif
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b . // loop until reset
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.size _reset, . - _reset
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.endfunc
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.end
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