start.s

RT-Thread是发展中的下一代微内核嵌入式实时操作系统

/*
 * File      : start.S
 * This file is part of RT-Thread RTOS
 * COPYRIGHT (C) 2006, RT-Thread Development Team
 *
 * The license and distribution terms for this file may be
 * found in the file LICENSE in this distribution or at
 * http://openlab.rt-thread.com/license/LICENSE
 *
 * Change Logs:
 * Date           Author       Notes
 * 2006-08-31     Bernard      first version
 */

	/* Internal Memory Base Addresses */
	.equ    FLASH_BASE,     0x00100000   
	.equ    RAM_BASE,       0x00200000

	/* Stack Configuration */
	.equ    TOP_STACK,      0x00204000
	.equ    UND_STACK_SIZE, 0x00000100
	.equ    SVC_STACK_SIZE, 0x00000400
	.equ    ABT_STACK_SIZE, 0x00000100
	.equ    FIQ_STACK_SIZE, 0x00000100
	.equ    IRQ_STACK_SIZE, 0x00000100
	.equ    USR_STACK_SIZE, 0x00000004

	/* ARM architecture definitions */
	.equ	MODE_USR, 0x10
	.equ	MODE_FIQ, 0x11
	.equ	MODE_IRQ, 0x12
	.equ	MODE_SVC, 0x13
	.equ	MODE_ABT, 0x17
	.equ	MODE_UND, 0x1B
	.equ	MODE_SYS, 0x1F

	.equ    I_BIT, 0x80    /* when this bit is set, IRQ is disabled */
	.equ    F_BIT, 0x40    /* when this bit is set, FIQ is disabled */

.section .init, "ax"
.code 32
.align 0
.globl _start
_start:
	b	reset
	ldr	pc, _vector_undef
	ldr	pc, _vector_swi
	ldr	pc, _vector_pabt
	ldr	pc, _vector_dabt
	nop							/* reserved vector */
	ldr	pc, _vector_irq
	ldr	pc, _vector_fiq

_vector_undef:	.word vector_undef
_vector_swi:	.word vector_swi
_vector_pabt:	.word vector_pabt
_vector_dabt:	.word vector_dabt
_vector_resv:	.word vector_resv
_vector_irq:	.word vector_irq
_vector_fiq:	.word vector_fiq

/*
 * rtthread bss start and end
 * which are defined in linker script
 */
.globl _bss_start
_bss_start:	.word __bss_start
.globl _bss_end
_bss_end:	.word __bss_end

/* the system entry */
reset:
	/* disable watchdog */
	ldr r0, =0xFFFFFD40
	ldr r1, =0x00008000
	str r1, [r0, #0x04]
	
	/* enable the main oscillator */
	ldr r0, =0xFFFFFC00
	ldr r1, =0x00000601
	str r1, [r0, #0x20]
	
	/* wait for main oscillator to stabilize */
moscs_loop:
	ldr r2, [r0, #0x68]
	ands r2, r2, #1
	beq moscs_loop
	
	/* set up the PLL */
	ldr r1, =0x00191C05
	str r1, [r0, #0x2C]
	
	/* wait for PLL to lock */
pll_loop:
	ldr r2, [r0, #0x68]
	ands r2, r2, #0x04
	beq pll_loop
	
	/* select clock */
	ldr r1, =0x00000007
	str r1, [r0, #0x30]
	
	/* setup stack for each mode */
	ldr r0, =TOP_STACK
	
	/* set stack */
	/* undefined instruction mode */
	msr cpsr_c, #MODE_UND|I_BIT|F_BIT
	mov sp, r0
	sub r0, r0, #UND_STACK_SIZE
	
	/* abort mode */
	msr cpsr_c, #MODE_ABT|I_BIT|F_BIT
	mov sp, r0
	sub r0, r0, #ABT_STACK_SIZE
	
	/* FIQ mode */
	msr cpsr_c, #MODE_FIQ|I_BIT|F_BIT
	mov sp, r0
	sub r0, r0, #FIQ_STACK_SIZE
	
	/* IRQ mode */
	msr cpsr_c, #MODE_IRQ|I_BIT|F_BIT
	mov sp, r0
	sub r0, r0, #IRQ_STACK_SIZE
	
	/* supervisor mode */
	msr cpsr_c, #MODE_SVC
	mov sp, r0

#ifdef __FLASH_BUILD__
	/* Relocate .data section (Copy from ROM to RAM) */
	ldr     r1, =_etext
	ldr     r2, =_data
	ldr     r3, =_edata
data_loop:
	cmp     r2, r3
	ldrlo   r0, [r1], #4
	strlo   r0, [r2], #4
	blo     data_loop
#else
	/* remap SRAM to 0x0000 */
	ldr r0, =0xFFFFFF00
	mov r1, #0x01
	str r1, [r0]
#endif

	/* mask all IRQs */
	ldr	r1, =0xFFFFF124
	ldr	r0, =0XFFFFFFFF
	str	r0, [r1]
	
	/* start RT-Thread Kernel */
	ldr	pc, _rtthread_startup
	
_rtthread_startup: .word rtthread_startup

/* exception handlers */
vector_undef: b	vector_undef
vector_swi  : b vector_swi
vector_pabt : b vector_pabt
vector_dabt : b vector_dabt
vector_resv : b vector_resv

.globl rt_interrupt_enter
.globl rt_interrupt_leave
.globl rt_thread_switch_interrput_flag
.globl rt_interrupt_from_thread
.globl rt_interrupt_to_thread
vector_irq:
	stmfd	sp!, {r0-r12,lr}
	bl	rt_interrupt_enter
	bl	rt_hw_trap_irq
	bl	rt_interrupt_leave

	/* 
	 * if rt_thread_switch_interrput_flag set, jump to
	 * rt_hw_context_switch_interrupt_do and don't return
	 */
	ldr	r0, =rt_thread_switch_interrput_flag
	ldr	r1, [r0]
	cmp	r1, #1
	beq	rt_hw_context_switch_interrupt_do

	ldmfd	sp!, {r0-r12,lr}
	subs	pc, lr, #4

vector_fiq:
	stmfd	sp!,{r0-r7,lr}
	bl 	rt_hw_trap_fiq
	ldmfd	sp!,{r0-r7,lr}
	subs	pc,lr,#4

/*
 * void rt_hw_context_switch_interrupt_do(rt_base_t flag)
 */
rt_hw_context_switch_interrupt_do:
	mov	r1,  #0				@ clear flag
	str	r1,  [r0]

	ldmfd	sp!, {r0-r12,lr}@ reload saved registers
	stmfd	sp!, {r0-r3}	@ save r0-r3
	mov	r1,  sp
	add	sp,  sp, #16		@ restore sp
	sub	r2,  lr, #4			@ save old task's pc to r2

	mrs	r3,  spsr			@ disable interrupt
	orr	r0,  r3, #I_BIT|F_BIT
	msr	spsr_c, r0

	ldr	r0,  =.+8			@ switch to interrupted task's stack
	movs	pc,  r0

	stmfd	sp!, {r2}		@ push old task's pc
	stmfd	sp!, {r4-r12,lr}@ push old task's lr,r12-r4
	mov	r4,  r1				@ Special optimised code below
	mov	r5,  r3
	ldmfd	r4!, {r0-r3}
	stmfd	sp!, {r0-r3}	@ push old task's r3-r0
	stmfd	sp!, {r5}		@ push old task's psr
	mrs	r4,  spsr
	stmfd	sp!, {r4}		@ push old task's spsr

	ldr	r4,  =rt_interrupt_from_thread
	ldr	r5,  [r4]
	str	sp,  [r5]			@ store sp in preempted tasks's TCB

	ldr	r6,  =rt_interrupt_to_thread
	ldr	r6,  [r6]
	ldr	sp,  [r6]			@ get new task's stack pointer

	ldmfd	sp!, {r4}		@ pop new task's spsr
	msr	SPSR_cxsf, r4
	ldmfd	sp!, {r4}		@ pop new task's psr
	msr	CPSR_cxsf, r4

	ldmfd	sp!, {r0-r12,lr,pc}	@ pop new task's r0-r12,lr & pc