Cortex-M3 (NXP LPC1788)之啟動程式碼分析
阿新 • • 發佈：2019-02-13
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。
自此分析了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 C語言函式執行。