前沿：
最近在做STM32的USB Bootlader/IAP功能，也就是通過USB實現(xiàn)固件升級，本文介紹下實現(xiàn)的基本思路，希望對實現(xiàn)IAP的同學一個參考，改方法已經(jīng)在產(chǎn)品中得到實際應用并驗證是比較合理，穩(wěn)定可靠的。

程序空間劃分：
在單片機的程序Flash中分兩個區(qū)，分別存儲Bootloader代碼和App代碼，Bootloader放到代碼起始地址，也就是0x08000000，App放到0x8020000地址，中間預留了很多的地址空間，主要是為了用來存儲一些需要掉電保存的數(shù)據(jù)，比如我在0x0800C000地址就存放了App程序運行后寫入該地址的標志數(shù)據(jù)。

啟動流程：
上電后自然是運行Bootloader程序，Bootloader運行后，做的第一件事情如下所示
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if((*((uint32_t *)EXE_FLAG_ADDR))==0x12345678){ ??JumpToApplication(APP_START_ADDR); }

也就是判斷App運行標志是否有效，這個標志是存放到EXE_FLAG_ADDR地址的，若有效就直接跳轉(zhuǎn)到App程序運行，這個時間很短，所以用戶看不到有Bootloader執(zhí)行的效果，感覺就是直接運行的App程序，進入App程序后，App程序第一件事情如下
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if((*((uint32_t *)EXE_FLAG_ADDR))==0xFFFFFFFF){ ??uint32_t ExeFlag = 0x12345678; ??__set_PRIMASK(1);//禁止全局中斷 ??FLASH_Unlock(); ??ProgramDatatoFlash(EXE_FLAG_ADDR,(uint8_t*)(&ExeFlag),4); ??FLASH_Lock(); }

也就是判斷App標志是否有效，若有效則直接執(zhí)行后面的程序，若無效則需要在EXE_FLAG_ADDR地址寫入執(zhí)行標志。
Bootloader程序判斷App標志若無效，那么Bootloader就不會直接跳轉(zhuǎn)到App，因為這個時候是需要進行升級App的操作，所以程序就進入Bootloader的正常工作流程，也就是等待升級App的各種命令，比如擦出固件，燒寫固件，校驗固件等。當固件成功寫入并校驗通過之后，PC端就可以發(fā)送一個程序跳轉(zhuǎn)命令跳轉(zhuǎn)到App執(zhí)行。

PC端操作流程：
PC端和單片機是通過USB進行數(shù)據(jù)交換的，當然用其他方式也可以，基本流程都是差不多的。
PC程序首先當然是掃描設備，打開設備，然后調(diào)用獲取固件信息的函數(shù)，調(diào)用該函數(shù)后可以得知當前固件的名稱，版本號，固件類型（Bootloader還是App），若發(fā)現(xiàn)當前固件不是Bootloader，那么就得通過USB給固件發(fā)送一個程序跳轉(zhuǎn)命令，也就是跳轉(zhuǎn)到Bootloader代碼執(zhí)行，當然App在跳轉(zhuǎn)到Bootloader的時候必須把EXE_FLAG_ADDR地址的標志數(shù)據(jù)擦出掉，這樣Bootloader才能進入正常的升級流程。
控制固件程序進入Bootloader之后，PC端程序?qū)⒋蜷_App固件程序文件，然后根據(jù)文件大小，發(fā)送擦出App代碼存儲區(qū)域Flash的數(shù)據(jù)，然后再分包將固件發(fā)送給單片機，單片機端Bootlader程序接收到數(shù)據(jù)后將數(shù)據(jù)寫入App的Flash區(qū)域，數(shù)據(jù)寫完之后再進行校驗，我是通過計算CRC16的方式進行校驗的，校驗通過之后就可以發(fā)送跳轉(zhuǎn)命令控制程序跳轉(zhuǎn)到App運行了，到此升級流程完畢。

PC端程序代碼：
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// USB2XXXTest.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include <stdlib.h> #include "../../USB2XXX/source/bootloader.h" int _tmain(int argc, _TCHAR* argv[]) { ????????int PackSize = 1024*10; ????????int TimeOut = 0; ????????int ApplicationAddress = 0x08020000; ????????int BootAddress = 0x08000000; ????????FW_INFO FwInfo; ????????bool state; ????????int ret; ????????//掃描查找設備 ????????ret = BT_ScanDevice(true); ????????if(ret <= 0){ ????????????????printf("No device connected!\n"); ????????????????return 0; ????????} ????????//打開設備 ????????state = BT_OpenDevice(0); ????????if(!state){ ????????????????printf("Open device error!\n"); ????????????????return 0; ????????} ????????//獲取固件信息 ????????BT_GetFirmwareInfo(0,&FwInfo); ????????printf("Firmware Name:%s\n",FwInfo.FirmwareName); ????????printf("Firmware Functions:%08X\n",FwInfo.Functions); ????????//判斷當前固件是否為Bootloader固件 ????????while(!(FwInfo.Functions&FUNCTION_BOOTLOADER)){ ????????????????//控制程序跳轉(zhuǎn)到Bootloader ????????????????state = BT_ExcuteFirmware(0,BootAddress); ????????????????printf("BT_ExcuteFirmware state = %d\n",state); ????????????????BT_CloseDevice(0); ????????? ????????????????do{ ????????????????????????Sleep(100); ????????????????????????ret = BT_ScanDevice(true);//掃描查找設備 ????????????????????????if((ret <= 0)&&(TimeOut > 50)){ ????????????????????????????????printf("No device connected!\n"); ????????????????????????????????return 0; ????????????????????????}else if(ret > 0){ ????????????????????????????????break; ????????????????????????} ????????????????????????TimeOut++; ????????????????}while(ret<=0); ????????????????TimeOut = 0; ????????????????do{ ????????????????????????Sleep(100); ????????????????????????state = BT_OpenDevice(0);//打開設備 ????????????????????????if((!state)&&(TimeOut > 50)){ ????????????????????????????????printf("Open device error!\n"); ????????????????????????????????return 0; ????????????????????????}else if(state){ ????????????????????????????????break; ????????????????????????} ????????????????????????TimeOut++; ????????????????}while(!state); ????????????????//獲取固件信息 ????????????????BT_GetFirmwareInfo(0,&FwInfo); ????????????????printf("Firmware Name:%s\n",FwInfo.FirmwareName); ????????????????printf("Firmware Functions:%08X\n",FwInfo.Functions); ????????} ????????//打開固件文件 ????????FILE *pFile=fopen("Project.bin","rb"); //獲取文件的指針 ????????fseek(pFile,0,SEEK_END); //把指針移動到文件的結(jié)尾 ，獲取文件長度 ????????int FileLen=ftell(pFile); //獲取文件長度 ????????static char *pBuf = (char *)malloc(FileLen);? //定義文件指針 ????????if(pBuf == NULL){ ????????????????printf("malloc error\n"); ????????????????return 0; ????????} ????????rewind(pFile); //把指針移動到文件開頭 因為我們一開始把指針移動到結(jié)尾，如果不移動回來 會出錯 ????????fread(pBuf,1,FileLen,pFile); //讀文件 ????????fclose(pFile); // 關閉文件 ????????//擦除之前的固件 ????????state = BT_EraseSectors(0,ApplicationAddress,ApplicationAddress+FileLen); ????????if(!state){ ????????????????printf("BT_EraseSectors error!\n"); ????????????????return 0; ????????}else{ ????????????????printf("BT_EraseSectors success\n"); ????????} ????????//循環(huán)寫入固件數(shù)據(jù)到芯片F(xiàn)lash ????????int PackIndex = 0; ????????for(PackIndex=0;PackIndex<FileLen/PackSize;PackIndex++){ ????????????????state = BT_WriteData(0,ApplicationAddress+PackIndex*PackSize,(unsigned char *)(&pBuf[PackIndex*PackSize]),PackSize,0); ????????????????if(!state){ ????????????????????????printf("BT_WriteData Error\n"); ????????????????????????return 0; ????????????????} ????????} ????????if(FileLen%PackSize){ ????????????????state = BT_WriteData(0,ApplicationAddress+PackIndex*PackSize,(unsigned char *)(&pBuf[PackIndex*PackSize]),FileLen%PackSize,0); ????????????????if(!state){ ????????????????????????printf("BT_WriteData Error\n"); ????????????????????????return 0; ????????????????} ????????} ????????printf("BT_WriteData Success\n"); ????????//循環(huán)校驗數(shù)據(jù)是否寫成功 ????????for(PackIndex=0;PackIndex<FileLen/PackSize;PackIndex++){ ????????????????state = BT_VerifyData(0,ApplicationAddress+PackIndex*PackSize,(unsigned char *)(&pBuf[PackIndex*PackSize]),PackSize); ????????????????if(!state){ ????????????????????????printf("BT_VerifyData Error\n"); ????????????????????????return 0; ????????????????} ????????} ????????if(FileLen%PackSize){ ????????????????state = BT_VerifyData(0,ApplicationAddress+PackIndex*PackSize,(unsigned char *)(&pBuf[PackIndex*PackSize]),FileLen%PackSize); ????????????????if(!state){ ????????????????????????printf("BT_VerifyData Error\n"); ????????????????????????return 0; ????????????????} ????????} ????????printf("BT_VerifyData Success\n"); ????????//執(zhí)行固件 ????????state = BT_ExcuteFirmware(0,ApplicationAddress); ????????printf("BT_ExcuteFirmware state = %d\n",state); ????????//關閉設備 ????????BT_CloseDevice(0); ????????return 0; }

PC端程序運行效果如下所示：
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后記：
我是用STM32F4+USB3300高速USB實現(xiàn)IAP功能的，12K的App代碼幾乎瞬間下載完畢，整個程序測試了很多次，沒一次出問題...

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