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Startup Code

Posted on : Sun , 08 2014 by : virusi

Theory on Startup Code :


Startup code is a small block of assembly language code that prepares the way for the execution of software written in a high-level language. Each high-level language has its own set of expectations about the runtime environment. For example, C both utilize an implicit stack. Space for the stack has to be allocated and initialized before software written in either language can be properly executed. The location and contents of this file are usually described in the documentation supplied with the compiler.

Startup code usually consists of the following actions :


– Initialize the stacks.

– Disable all interrupts.

– Copy any initialized data from ROM to RAM.

– Zero the uninitialized data area.

– Allocate space for and initialize the stack.

– Enable interrupts.

– Initialize the heap.

– Call constructors.

– Initialize the .bss section to zero.

– If compiled with FULL_LIBRARY, get the command line from the host using debug_getargs and set registers to supply argc and argv to main.

– Call main.

On return from main or when exit is called :


– If compiled with FULL_LIBRARY, call destructors.

– If compiled with FULL_LIBRARY, call atexit functions.

– If compiled with FULL_LIBRARY, call debug_exit while supplying the return result from main.

– Wait in exit loop.

The instruction from the main code will be executed only in the event that the high-level language program exits Depending on the nature of the embedded system, you might want to use these instructions to halt the processor, reset the entire system, or transfer control to a debugging tool.

Because the startup code is not inserted automatically, the programmer must usually assemble it himself and include the resulting object file among the list of input files to the linker. Every microcontroller has its own startup code, so before creating a project make sure you have the necessary startup code for the specific microcontroller.

LIC1768 PRACTICAL EXAMPLE :


As we have discussed earlier the start up code is not included automatically this is why we need to include it in our project.

If you are using uVision than the startup code is included when you create a new project and add startup_LPC17xx.s file to the project.

4. Create each component as in the source folder.

components
Fig. 1 Components Structure.
Let’s open the startup code :
 ;/*****************************************************************************
; * @file:    startup_LPC17xx.s
; * @purpose: CMSIS Cortex-M3 Core Device Startup File 
; *           for the NXP LPC17xx Device Series 
; * @version: V1.02
; * @date:    27. July 2009
; *------- <<< Use Configuration Wizard in Context Menu >>> ------------------
; *
; * Copyright (C) 2009 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.
; *
; *****************************************************************************/

;  Stack Configuration
;    Stack Size (in Bytes) 
; 

Stack_Size      EQU     0x00000200

                AREA    STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem       SPACE   Stack_Size
__initial_sp

;  Heap Configuration
;     Heap Size (in Bytes) 
; 

Heap_Size       EQU     0x00000000
                AREA    HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem        SPACE   Heap_Size
__heap_limit

                PRESERVE8
                THUMB
					 	; FreeRTOS specific handlers.
					 	EXTERN 	vPortSVCHandler
						EXTERN  xPortPendSVHandler
						EXTERN  xPortSysTickHandler

; 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     vPortSVCHandler           ; SVCall Handler
                DCD     DebugMon_Handler          ; Debug Monitor Handler
                DCD     0                         ; Reserved
                DCD     xPortPendSVHandler        ; PendSV Handler
                DCD     xPortSysTickHandler       ; 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     SPI_IRQHandler            ; 29: SPI
                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     RIT_IRQHandler            ; 45: Repetitive Interrupt Timer
                DCD     MCPWM_IRQHandler          ; 46: Motor Control PWM
                DCD     QEI_IRQHandler            ; 47: Quadrature Encoder Interface
                DCD     PLL1_IRQHandler           ; 48: PLL1 Lock (USB PLL)


                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  SPI_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  RIT_IRQHandler            [WEAK]
                EXPORT  MCPWM_IRQHandler          [WEAK]
                EXPORT  QEI_IRQHandler            [WEAK]
                EXPORT  PLL1_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           
SPI_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       
RIT_IRQHandler          
MCPWM_IRQHandler             
QEI_IRQHandler            
PLL1_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
As you can see the start up code contains :

– Heap Size.

– Vector Table.

– Reset Handler.

– NMI Handler.

– etc.

Last updated on Sun , 09 2014
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