?? crt0.s
字號:
/*
crt0.S for LPC2xxx
- based on examples from R O Software
- based on examples from newlib-lpc
- based on an example from Anglia Designs
collected and modified by Martin Thomas
*/
.global _etext // -> .data initial values in ROM
.global _data // -> .data area in RAM
.global _edata // end of .data area
.global __bss_start // -> .bss area in RAM
.global __bss_end__ // end of .bss area
.global _stack // top of stack
// Stack Sizes
.set UND_STACK_SIZE, 0x00000004
.set ABT_STACK_SIZE, 0x00000004
.set FIQ_STACK_SIZE, 0x00000004
.set IRQ_STACK_SIZE, 0X00000080
.set SVC_STACK_SIZE, 0x00000004
// Standard definitions of Mode bits and Interrupt (I & F) flags in PSRs
.set MODE_USR, 0x10 // User Mode
.set MODE_FIQ, 0x11 // FIQ Mode
.set MODE_IRQ, 0x12 // IRQ Mode
.set MODE_SVC, 0x13 // Supervisor Mode
.set MODE_ABT, 0x17 // Abort Mode
.set MODE_UND, 0x1B // Undefined Mode
.set MODE_SYS, 0x1F // System Mode
.equ I_BIT, 0x80 // when I bit is set, IRQ is disabled
.equ F_BIT, 0x40 // when F bit is set, FIQ is disabled
.text
.arm
.section .init, "ax"
.code 32
.align 2
.global _boot
.func _boot
_boot:
// Runtime Interrupt Vectors
// -------------------------
Vectors:
b _start // reset - _start
ldr pc,_undf // undefined - _undf
ldr pc,_swi // SWI - _swi
ldr pc,_pabt // program abort - _pabt
ldr pc,_dabt // data abort - _dabt
nop // reserved
ldr pc,[pc,#-0xFF0] // IRQ - read the VIC
ldr pc,_fiq // FIQ - _fiq
#if 0
// Use this group for production
_undf: .word _reset // undefined - _reset
_swi: .word _reset // SWI - _reset
_pabt: .word _reset // program abort - _reset
_dabt: .word _reset // data abort - _reset
_irq: .word _reset // IRQ - _reset
_fiq: .word _reset // FIQ - _reset
#else
// Use this group for development
_undf: .word __undf // undefined
_swi: .word __swi // SWI
_pabt: .word __pabt // program abort
_dabt: .word __dabt // data abort
_irq: .word __irq // IRQ
_fiq: .word __fiq // FIQ
__undf: b . // undefined
__swi: b . // SWI
__pabt: b . // program abort
__dabt: b . // data abort
__irq: b . // IRQ
__fiq: b . // FIQ
#endif
.size _boot, . - _boot
.endfunc
// Setup the operating mode & stack.
// ---------------------------------
.global _start, start, _mainCRTStartup
.func _start
_start:
start:
_mainCRTStartup:
// Initialize Interrupt System
// - Set stack location for each mode
// - Leave in System Mode with Interrupts Disabled
// -----------------------------------------------
ldr r0,=_stack
msr CPSR_c,#MODE_UND|I_BIT|F_BIT // Undefined Instruction Mode
mov sp,r0
sub r0,r0,#UND_STACK_SIZE
msr CPSR_c,#MODE_ABT|I_BIT|F_BIT // Abort Mode
mov sp,r0
sub r0,r0,#ABT_STACK_SIZE
msr CPSR_c,#MODE_FIQ|I_BIT|F_BIT // FIQ Mode
mov sp,r0
sub r0,r0,#FIQ_STACK_SIZE
msr CPSR_c,#MODE_IRQ|I_BIT|F_BIT // IRQ Mode
mov sp,r0
sub r0,r0,#IRQ_STACK_SIZE
msr CPSR_c,#MODE_SVC|I_BIT|F_BIT // Supervisor Mode
mov sp,r0
sub r0,r0,#SVC_STACK_SIZE
msr CPSR_c,#MODE_SYS|I_BIT|F_BIT // System Mode
mov sp,r0
// Copy initialized data to its execution address in RAM
// -----------------------------------------------------
#ifdef ROM_RUN
ldr r1,=_etext // -> ROM data start
ldr r2,=_data // -> data start
ldr r3,=_edata // -> end of data
1: cmp r2,r3 // check if data to move
ldrlo r0,[r1],#4 // copy it
strlo r0,[r2],#4
blo 1b // loop until done
#endif
// Clear .bss
// ----------
mov r0,#0 // get a zero
ldr r1,=__bss_start // -> bss start
ldr r2,=__bss_end__ // -> bss end
2: cmp r1,r2 // check if data to clear
strlo r0,[r1],#4 // clear 4 bytes
blo 2b // loop until done
/*
Call C++ constructors (for objects in "global scope")
ctor loop added by Martin Thomas 4/2005
based on a Anglia Design example-application for ST ARM
*/
LDR r0, =__ctors_start__
LDR r1, =__ctors_end__
ctor_loop:
CMP r0, r1
BEQ ctor_end
LDR r2, [r0], #4
STMFD sp!, {r0-r1}
MOV lr, pc
MOV pc, r2
LDMFD sp!, {r0-r1}
B ctor_loop
ctor_end:
// Call main program: main(0)
// --------------------------
mov r0,#0 // no arguments (argc = 0)
mov r1,r0
mov r2,r0
mov fp,r0 // null frame pointer
mov r7,r0 // null frame pointer for thumb
ldr r10,=main
mov lr,pc
/* Enter the C code, use BX instruction so as to never return */
/* use BLX (?) main if you want to use c++ destructors below */
bx r10 // enter main()
/* "global object"-dtors are never called and it should not be
needed since there is no OS to exit to. */
/* Call destructors */
# LDR r0, =__dtors_start__
# LDR r1, =__dtors_end__
dtor_loop:
# CMP r0, r1
# BEQ dtor_end
# LDR r2, [r0], #4
# STMFD sp!, {r0-r1}
# MOV lr, pc
# MOV pc, r2
# LDMFD sp!, {r0-r1}
# B dtor_loop
dtor_end:
.size _start, . - _start
.endfunc
.global _reset, reset, exit, abort
.func _reset
_reset:
reset:
exit:
abort:
#if 0
// Disable interrupts, then force a hardware reset by driving P23 low
// -------------------------------------------------------------------
mrs r0,cpsr // get PSR
orr r0,r0,#I_BIT|F_BIT // disable IRQ and FIQ
msr cpsr,r0 // set up status register
ldr r1,=(PS_BASE) // PS Base Address
ldr r0,=(PS_PIO) // PIO Module
str r0,[r1,#PS_PCER_OFF] // enable its clock
ldr r1,=(PIO_BASE) // PIO Base Address
ldr r0,=(1<<23) // P23
str r0,[r1,#PIO_PER_OFF] // make sure pin is contolled by PIO
str r0,[r1,#PIO_CODR_OFF] // set the pin low
str r0,[r1,#PIO_OER_OFF] // make it an output
#endif
b . // loop until reset
.size _reset, . - _reset
.endfunc
.end
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