Cortex-M3 (NXP LPC1788)之啟動程式碼分析
技術標籤:LPC1788
在Keil uVision4中新建一個基於NXP1788的工程後,會提示新增啟動彙編程式碼startup_LPC177x_8x.S。該檔案進行從彙編到C語言執行環境的初始化工作。
;/*****************************************************************************
; * @file: startup_LPC177x_8x.s
; * @purpose: CMSIS Cortex-M3 Core Device Startup File
; * for the NXP LPC177x_8x Device Series
; * @version: V1.20
; * @date: 07. October 2010
; *------- <<< Use Configuration Wizard in Context Menu >>> ------------------
; *
; * Copyright (C) 2010 ARM Limited. All rights reserved.
; * ARM Limited (ARM) is supplying this software for use with Cortex-M3
; * processor based microcontrollers. This file can be freely distributed
; * within development tools that are supporting such ARM based processors.
; *
; * THIS SOFTWARE IS PROVIDED "AS IS". NO WARRANTIES, WHETHER EXPRESS, IMPLIED
; * OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF
; * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE.
; * ARM SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL, OR
; * CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
; *
; *****************************************************************************/
; <h> Stack Configuration
; <o> Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>
Stack_Size EQU 0x00000200
AREA STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem SPACE Stack_Size
__initial_sp
; <h> Heap Configuration
; <o> Heap Size ( in Bytes) <0x0-0xFFFFFFFF:8>
; </h>
Heap_Size EQU 0x00000400
AREA HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem SPACE Heap_Size
__heap_limit
PRESERVE8
THUMB
; Vector Table Mapped to Address 0 at Reset
AREA RESET, DATA, READONLY
EXPORT __Vectors
__Vectors DCD __initial_sp ; Top of Stack
DCD Reset_Handler ; Reset Handler
DCD NMI_Handler ; NMI Handler
DCD HardFault_Handler ; Hard Fault Handler
DCD MemManage_Handler ; MPU Fault Handler
DCD BusFault_Handler ; Bus Fault Handler
DCD UsageFault_Handler ; Usage Fault Handler
DCD 0 ; Reserved
DCD 0 ; Reserved
DCD 0 ; Reserved
DCD 0 ; Reserved
DCD SVC_Handler ; SVCall Handler
DCD DebugMon_Handler ; Debug Monitor Handler
DCD 0 ; Reserved
DCD PendSV_Handler ; PendSV Handler
DCD SysTick_Handler ; SysTick Handler
; External Interrupts
DCD WDT_IRQHandler ; 16: Watchdog Timer
DCD TIMER0_IRQHandler ; 17: Timer0
DCD TIMER1_IRQHandler ; 18: Timer1
DCD TIMER2_IRQHandler ; 19: Timer2
DCD TIMER3_IRQHandler ; 20: Timer3
DCD UART0_IRQHandler ; 21: UART0
DCD UART1_IRQHandler ; 22: UART1
DCD UART2_IRQHandler ; 23: UART2
DCD UART3_IRQHandler ; 24: UART3
DCD PWM1_IRQHandler ; 25: PWM1
DCD I2C0_IRQHandler ; 26: I2C0
DCD I2C1_IRQHandler ; 27: I2C1
DCD I2C2_IRQHandler ; 28: I2C2
DCD SPIFI_IRQHandler ; 29: SPIFI
DCD SSP0_IRQHandler ; 30: SSP0
DCD SSP1_IRQHandler ; 31: SSP1
DCD PLL0_IRQHandler ; 32: PLL0 Lock (Main PLL)
DCD RTC_IRQHandler ; 33: Real Time Clock
DCD EINT0_IRQHandler ; 34: External Interrupt 0
DCD EINT1_IRQHandler ; 35: External Interrupt 1
DCD EINT2_IRQHandler ; 36: External Interrupt 2
DCD EINT3_IRQHandler ; 37: External Interrupt 3
DCD ADC_IRQHandler ; 38: A/D Converter
DCD BOD_IRQHandler ; 39: Brown-Out Detect
DCD USB_IRQHandler ; 40: USB
DCD CAN_IRQHandler ; 41: CAN
DCD DMA_IRQHandler ; 42: General Purpose DMA
DCD I2S_IRQHandler ; 43: I2S
DCD ENET_IRQHandler ; 44: Ethernet
DCD MCI_IRQHandler ; 45: SD/MMC card I/F
DCD MCPWM_IRQHandler ; 46: Motor Control PWM
DCD QEI_IRQHandler ; 47: Quadrature Encoder Interface
DCD PLL1_IRQHandler ; 48: PLL1 Lock (USB PLL)
DCD USBActivity_IRQHandler ; 49: USB Activity interrupt to wakeup
DCD CANActivity_IRQHandler ; 50: CAN Activity interrupt to wakeup
DCD UART4_IRQHandler ; 51: UART4
DCD SSP2_IRQHandler ; 52: SSP2
DCD LCD_IRQHandler ; 53: LCD
DCD GPIO_IRQHandler ; 54: GPIO
DCD PWM0_IRQHandler ; 55: PWM0
DCD EEPROM_IRQHandler ; 56: EEPROM
IF :LNOT::DEF:NO_CRP
AREA |.ARM.__at_0x02FC|, CODE, READONLY
CRP_Key DCD 0xFFFFFFFF
ENDIF
AREA |.text|, CODE, READONLY
; Reset Handler
Reset_Handler PROC
EXPORT Reset_Handler [WEAK]
IMPORT SystemInit
IMPORT __main
LDR R0, =SystemInit
BLX R0
LDR R0, =__main
BX R0
ENDP
; Dummy Exception Handlers (infinite loops which can be modified)
NMI_Handler PROC
EXPORT NMI_Handler [WEAK]
B .
ENDP
HardFault_Handler\
PROC
EXPORT HardFault_Handler [WEAK]
B .
ENDP
MemManage_Handler\
PROC
EXPORT MemManage_Handler [WEAK]
B .
ENDP
BusFault_Handler\
PROC
EXPORT BusFault_Handler [WEAK]
B .
ENDP
UsageFault_Handler\
PROC
EXPORT UsageFault_Handler [WEAK]
B .
ENDP
SVC_Handler PROC
EXPORT SVC_Handler [WEAK]
B .
ENDP
DebugMon_Handler\
PROC
EXPORT DebugMon_Handler [WEAK]
B .
ENDP
PendSV_Handler PROC
EXPORT PendSV_Handler [WEAK]
B .
ENDP
SysTick_Handler PROC
EXPORT SysTick_Handler [WEAK]
B .
ENDP
Default_Handler PROC
EXPORT WDT_IRQHandler [WEAK]
EXPORT TIMER0_IRQHandler [WEAK]
EXPORT TIMER1_IRQHandler [WEAK]
EXPORT TIMER2_IRQHandler [WEAK]
EXPORT TIMER3_IRQHandler [WEAK]
EXPORT UART0_IRQHandler [WEAK]
EXPORT UART1_IRQHandler [WEAK]
EXPORT UART2_IRQHandler [WEAK]
EXPORT UART3_IRQHandler [WEAK]
EXPORT PWM1_IRQHandler [WEAK]
EXPORT I2C0_IRQHandler [WEAK]
EXPORT I2C1_IRQHandler [WEAK]
EXPORT I2C2_IRQHandler [WEAK]
EXPORT SPIFI_IRQHandler [WEAK]
EXPORT SSP0_IRQHandler [WEAK]
EXPORT SSP1_IRQHandler [WEAK]
EXPORT PLL0_IRQHandler [WEAK]
EXPORT RTC_IRQHandler [WEAK]
EXPORT EINT0_IRQHandler [WEAK]
EXPORT EINT1_IRQHandler [WEAK]
EXPORT EINT2_IRQHandler [WEAK]
EXPORT EINT3_IRQHandler [WEAK]
EXPORT ADC_IRQHandler [WEAK]
EXPORT BOD_IRQHandler [WEAK]
EXPORT USB_IRQHandler [WEAK]
EXPORT CAN_IRQHandler [WEAK]
EXPORT DMA_IRQHandler [WEAK]
EXPORT I2S_IRQHandler [WEAK]
EXPORT ENET_IRQHandler [WEAK]
EXPORT MCI_IRQHandler [WEAK]
EXPORT MCPWM_IRQHandler [WEAK]
EXPORT QEI_IRQHandler [WEAK]
EXPORT PLL1_IRQHandler [WEAK]
EXPORT USBActivity_IRQHandler [WEAK]
EXPORT CANActivity_IRQHandler [WEAK]
EXPORT UART4_IRQHandler [WEAK]
EXPORT SSP2_IRQHandler [WEAK]
EXPORT LCD_IRQHandler [WEAK]
EXPORT GPIO_IRQHandler [WEAK]
EXPORT PWM0_IRQHandler [WEAK]
EXPORT EEPROM_IRQHandler [WEAK]
WDT_IRQHandler
TIMER0_IRQHandler
TIMER1_IRQHandler
TIMER2_IRQHandler
TIMER3_IRQHandler
UART0_IRQHandler
UART1_IRQHandler
UART2_IRQHandler
UART3_IRQHandler
PWM1_IRQHandler
I2C0_IRQHandler
I2C1_IRQHandler
I2C2_IRQHandler
SPIFI_IRQHandler
SSP0_IRQHandler
SSP1_IRQHandler
PLL0_IRQHandler
RTC_IRQHandler
EINT0_IRQHandler
EINT1_IRQHandler
EINT2_IRQHandler
EINT3_IRQHandler
ADC_IRQHandler
BOD_IRQHandler
USB_IRQHandler
CAN_IRQHandler
DMA_IRQHandler
I2S_IRQHandler
ENET_IRQHandler
MCI_IRQHandler
MCPWM_IRQHandler
QEI_IRQHandler
PLL1_IRQHandler
USBActivity_IRQHandler
CANActivity_IRQHandler
UART4_IRQHandler
SSP2_IRQHandler
LCD_IRQHandler
GPIO_IRQHandler
PWM0_IRQHandler
EEPROM_IRQHandler
B .
ENDP
ALIGN
; User Initial Stack & Heap
IF :DEF:__MICROLIB
EXPORT __initial_sp
EXPORT __heap_base
EXPORT __heap_limit
ELSE
IMPORT __use_two_region_memory
EXPORT __user_initial_stackheap
__user_initial_stackheap
LDR R0, = Heap_Mem
LDR R1, =(Stack_Mem + Stack_Size)
LDR R2, = (Heap_Mem + Heap_Size)
LDR R3, = Stack_Mem
BX LR
ALIGN
ENDIF
END
程式完成如下內容的工作:
-
開闢一塊大小為Stack_Size的棧空間;
-
標號__initial_sp指向棧頂位置;
-
定義堆空間大小為Heap_Size;
建立中斷向量表Vectors,cortex-M3規定起始地址必須存放棧頂地址即__initial_sp,緊接著存放復位入口地址,這樣核心復位後就會自動從起始地址的下32位取出復位地址執行復位中斷服務函式。
Reset_Handler復位中斷函式中先EXPORT宣告Reset_Handler的全域性性,然後分別執行外部的函式SystemInit和__main。
下面對彙編程式中的幾個關鍵字做說明:
AREA偽指令:用於定義程式碼段和資料段,後跟屬性標號。其中“READWRITE”表示可讀寫,“READONLY”只讀屬性。根據LPC1788的資料手冊描述的儲存介質,可知可讀寫段保持在SRAM區,起始地址為0x1000 0000,程式碼中的堆疊儲存在SRAM空間。只讀段儲存在Flash區,起始地址為0x0000 0000,程式碼中的中斷向量表儲存在Flash空間。 因此可以總結出,在0x0000 0000 存放的是棧頂的地址__initial_sp(即0x1000 0200),在0x0000 0004 存放的是Reset_Handler的地址。
圖1:LPC1788 地址對映
圖2: debug中 0地址的值0x1000 0200 即棧頂地址, 0x0000 0004 地址值為0x0000 00F9(看反彙編可知該值 即Reset_Handler的入口如下圖)。
DCD指令:開闢記憶體空間,中斷向量表建立中使用相當於C語言中的函式指標,每個成員都是函式指標,指向各個中斷服務函式。
以上分析了LPC1788的啟動,主要包括堆疊初始化,和中斷向量表的初始化。LPC1788有內部Flash,所以上點從內部Flash啟動,內部Flash的起始地址為0x0000 0000,存放棧頂的地址0x1000 0200。 0x0000 0004存放復位中斷的入口地址。LPC1788復位後,從0x0000 0004取出復位入口地址,執行中斷復位函式,從而跳轉到SystemInit和main 函式執行。