2021年07月15日 | MC9S12XEP 的bootloader解析

MC9S12XEP 的bootloader 归纳总结 两个要点：

1.ROM不要重叠，bootloader的代码与用户应用代码不要重叠。各自设置各自的ROM区域;

2.bootloader有一部分代码是在RAM里运行的，所以RAM也不能重叠，RAM可以分为如下三种：

       a.) 堆栈区域;

       b.)bootloader代码变量区域;

       c.)bootloader 中断地址;

      上述三种RAM类型，不可重叠。

先说bootloader部分，需要处理的步骤如下：

a). 为 bootloader 划出ROM，（.prm文件修改）

b). 为bootloader ROM里再划出一块区域，程序运行时，这个区域里的CODE会被复制到RAM里执行;（.prm文件修改）

c).中断向量映射。地址保存在RAM里，所以，这个RAM与上面存放代码的RAM以及程序运行时的RAM都不要重叠;（.c文件，程序里定义）

d).需要在RAM运行的代码，拷贝到RAM里; （.c文件，程序里操作）

下面是一个project.prm 文件，（这里的地址值用的是 逻辑地址）

INIT _BootStart

NAMES END 

SEGMENTS  /* Here all RAM/ROM areas of the device are listed. Used in PLACEMENT below. */

      /* 

      Area 0x3800-0x38FF is reserved for stack. Stack pointer is initialized in StartS12X.s file

      to initail value 0x3900.

      Area 0x3900-0x3CFF is used for standard purposes.      

      Area 0x3D00-0x3EFF is used for functions that must be executed from RAM memory. These functions

      are stored in flash memory in RAM_CODE_SEG (see below) and are copied to RAM memory after startup. 

      Area 0x3F00-0x3FFF is used for interrupt vector table.

      */            

      RAM           = READ_WRITE    0x3000 TO   0x36FF;      

      RAM_CODE_SEG  = READ_ONLY     0xFA00 TO   0xFEFF RELOCATE_TO 0x3700;      

      ROM_F000      = READ_ONLY     0xE000 TO   0xF9FF;

END

PLACEMENT /* here all predefined and user segments are placed into the SEGMENTS defined above. */

      ROM_VAR,  

      STRINGS,  

      DEFAULT_ROM,

      NON_BANKED      INTO  ROM_F000;

      DEFAULT_RAM     INTO  RAM;

      RAM_CODE        INTO  RAM_CODE_SEG;

END

ENTRIES

  flash_array

END

STACKSIZE 0x100

//handle all reset vectors 

VECTOR 0 _BootStart

VECTOR 1 _BootStart

VECTOR 2 _BootStart

文件里有这样的字样

      RAM           = READ_WRITE    0x3000 TO   0x36FF;      

      RAM_CODE_SEG  = READ_ONLY     0xFA00 TO   0xFEFF RELOCATE_TO 0x3700;      

      ROM_F000      = READ_ONLY     0xE000 TO   0xF9FF; 

 RAM = READ_WRITE 0X3000 TO 0X36FF    表示代码运行时，可以自由支配使用的RAM区域; 

 其中，0X3000 需要与 .S文件里的 堆栈 设置 相匹配。在.S文件里，如下

;********************************************************************************

;* Freescale Semiconductor Inc.

;* (c) Copyright 2004-2005 Freescale Semiconductor, Inc.

;* ALL RIGHTS RESERVED.

;********************************************************************************

;Services performed by FREESCALE in this matter are performed AS IS and without 

;any warranty. CUSTOMER retains the final decision relative to the total design 

;and functionality of the end product. FREESCALE neither guarantees nor will be 

;held liable by CUSTOMER for the success of this project.

;FREESCALE DISCLAIMS ALL WARRANTIES, EXPRESSED, IMPLIED OR STATUTORY INCLUDING, 

;BUT NOT LIMITED TO, IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR 

;A PARTICULAR PURPOSE ON ANY HARDWARE, SOFTWARE OR ADVISE SUPPLIED TO THE PROJECT

;BY FREESCALE, AND OR NAY PRODUCT RESULTING FROM FREESCALE SERVICES. IN NO EVENT

;SHALL FREESCALE BE LIABLE FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF 

;THIS AGREEMENT.

;

;CUSTOMER agrees to hold FREESCALE harmless against any and all claims demands or 

;actions by anyone on account of any damage, or injury, whether commercial, 

;contractual, or tortuous, rising directly or indirectly as a result of an advise

;or assistance supplied CUSTOMER in connection with product, services or goods 

;supplied under this Agreement.

;********************************************************************************

;* File      StartS12X.s

;* Owner     b01802

;* Version   1.0   

;* Date      Dec-02-2010

;* Classification   General Business Information

;* Brief     Startup file

;********************************************************************************

;* Detailed Description:

;*

;*    Tested on: DEMO9S12XSFAME, EVB9S12XEP100

;*    

;*    The bootloder handles all reset vectors. This startup file makes a decision

;*    whether the bootloader or user application is executed. 

;********************************************************************************

;Revision History:

;Version   Date          Author    Description of Changes

;1.0       Dec-02-2010  b01802    Initial version

;********************************************************************************

;

  xref  main

;

  xdef  _BootStart

;

AppResetVect:   equ     $effe ; here is stored reset vector of user application

StackTop:       equ     $3000 

_BootStart:

  ; -----------------------------------------------------------------------------

  movb  #$01, $025C ; enable pull up resistor on PP0 (or we can use external one)

  nop   ;wait a few cycles for stabilization of the signal

  nop

  nop

  nop

  nop

  brclr $0259, $01, GoBoot  ; if PP0 == 0 then start the bootloader

                            ; if PP0 == 1 then start the application

  movb  #$00, $025C ; disable pull up resistor on pin PP0 - restore default state

  ; -----------------------------------------------------------------------------

  ldd   AppResetVect

  cpd   #$ffff

  beq   GoBoot          ; if the application reset vector is not available

                        ; then start the bootloader

  ldx   AppResetVect

  jmp    0,x              ; jump to the application

GoBoot:

  lds  #StackTop

  jmp  main

;********************************************************************************

.S文件里的  “ StackTop:       equ     $3000 ” 表示堆栈值是 0X3000 与上述的.prm文件里的  RAM = READ_WRITE 0X3000 TO 0X36FF 相对应，因为.prm文件里定义了堆栈层数是是0X100("STACKSIZE 0x100")，所以 堆栈的地址区域是 0X2F00 ~ 0X3000 ，显然这个区域是专用的.