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中国linux公社 - 基于atmel at91rm9200的armlinux的bootloader启动代码分析

2005-08-17  andrew2008
基于Atmel at91rm9200的armlinux的bootloader启动代码分析
  贴出者为 balancesli
编程开发 balancesli写著 ‘ 前阶段做了一次基于at91rm9200引导部分的技术分析,主要采用了u-boot,这里只面向使用at91rm9200板子的的朋友做个简单的推敲,希望起到抛砖引玉的作用

Author : balancesli
mail : balancesli@thizlinux.com.cn

前阶段做了一次基于at91rm9200引导部分的技术分析,主要采用了u-boot,这里只面向使用at91rm9200板子的
的朋友做个简单的推敲,希望起到抛砖引玉的作用.

关键词 :
u-boot: 一个开源的面向多个目标平台(ppc, mips, arm, x86)的bootloader.
at91rm9200 : Atmel 公司生产的基于arm9核的Soc处理器.

以下先给出at91rm9200引导流程图

Boot program Flow Diagram

Device Setup
|
|
Boot SPI DataFlash Boot --> Download from DataFlash --> run
|
|
TWI EEPROM Boot --> Download from EEPROM --> run
|
|
Parallel Boot --> Download from 8-bit Device -->
|
| Xmodem protocol
| |---DBGU Serial Download ---------------------> run
|____|
| DFU protocol
|-----USB download -----------------------> run

在这里我主要介绍通过片内引导和片外引导, 片内引导主要采用串口下载并引导u-boot,并完成程序被烧写到Flash上,
然后就可以通过跳线的方式从片外引导执行已经烧写到片外Flash上的引导程序(bootloader).

这里要提及的是at91rm9200内部本身有128k的片内rom,其固化了一个bootloader和uploader, 用来支持程序的
下载和引导,而且其内部固化的程序提供了很多内部服务接口(Internel Service)供我们来使用,例如Xmodem,Tempo
DataFlash, CRC, Sine服务接口,这样我们就可以利用它所提供的Service interface API完成程序的下载。
这里主要介绍Xmodem接口服务。

at91rm9200内部固化的代码在设计上采用了面向对象的设计方法,如下:


typedef struct _AT91S_Service
{
char data;
char (*MainMethod)();
char (*ChildMethod)();
}AT91S_Service, *AT91PS_Service;

char AT91F_MainMethod()
{

}
char AT91F_ChildMethod()
{

}

/*init the Service */
AT91PS_Service AT91F_OpenDevice(AT91PS_Service pService)
{
pService->data = 0;
pService->MainMethod = AT91F_MainMethod;
pService->ChildMethod = AT91F_ChildMethod;
}

//使用方法如下
AT91S_Service service;
AT91PS_Service pService = AT91F_OpenDevice(&service);
pService->AT91F_MainMethmod();
.....

通过如上代码片断可以看出它采用了类似面向对象的设计方法。
其实如果各位朋友接触过的话或者看过这本书的话,应该很容易便接受它。
下面以Xmodem服务为例子介绍:


at91rm9200内部提供的服务包含了几个服务对象, 这些对象在片内启动xmodem协议Host端和Targe端通讯时会用到.


typedef struct _AT91S_RomBoot
{
const unsigned int version;
// Peripheral descriptors
const AT91S_MEMCDesc MEMC_DESC;
const AT91S_STDesc SYSTIMER_DESC;
const AT91S_Pio2Desc PIOA_DESC;
const AT91S_Pio2Desc PIOB_DESC;
const AT91S_USART2Desc DBGU_DESC;
const AT91S_USART2Desc USART0_DESC;
const AT91S_USART2Desc USART1_DESC;
const AT91S_USART2Desc USART2_DESC;
const AT91S_USART2Desc USART3_DESC;
const AT91S_TWIDesc TWI_DESC;
const AT91S_SPIDesc SPI_DESC;

// Objects entry
const AT91PF_OpenPipe OpenPipe;
const AT91PF_OpenSBuffer OpenSBuffer;
const AT91PF_OpenSvcUdp OpenSvcUdp;
const AT91PF_OpenSvcXmodem OpenSvcXmodem;
const AT91PF_OpenCtlTempo OpenCtlTempo;
const AT91PF_OpenDfuDesc OpenDfuDesc;
const AT91PF_OpenUsbDesc OpenUsbDesc;
const AT91PF_OpenSvcDataFlash OpenSvcDataFlash;
const AT91PF_SVC_CRC16 CRC16;
const AT91PF_SVC_CRCCCITT CRCCCITT;
const AT91PF_SVC_CRCHDLC CRCHDLC;
const AT91PF_SVC_CRC32 CRC32;
// Array
const AT91PS_SVC_CRC_BIT_REV Bit_Reverse_Array;
const AT91PS_SINE_TAB SineTab;
const AT91PF_Sinus Sine;
} AT91S_RomBoot;

//AT91S_Pipe
typedef struct _AT91S_Pipe
{
// A pipe is linked with a peripheral and a buffer
AT91PS_SvcComm pSvcComm;
AT91PS_Buffer pBuffer;

// Callback functions with their arguments
void (*WriteCallback) (AT91S_PipeStatus, void *);
void (*ReadCallback) (AT91S_PipeStatus, void *);
void *pPrivateReadData;
void *pPrivateWriteData;

// Pipe methods
AT91S_PipeStatus (*Write) (
struct _AT91S_Pipe *pPipe,
char const * pData,
unsigned int size,
void (*callback) (AT91S_PipeStatus, void *),
void *privateData
);

AT91S_PipeStatus (*Read) (
struct _AT91S_Pipe *pPipe,
char *pData,
unsigned int size,
void (*callback) (AT91S_PipeStatus, void *),
void *privateData
);

AT91S_PipeStatus (*AbortWrite)(struct _AT91S_Pipe *pPipe);
AT91S_PipeStatus (*AbortRead)(struct _AT91S_Pipe *pPipe);
AT91S_PipeStatus (*AbortRead)(struct _AT91S_Pipe *pPipe);
AT91S_PipeStatus (*Reset)(struct _AT91S_Pipe *pPipe);
char (*IsWritten)(struct _AT91S_Pipe *pPipe, char const *pVoid);
char (*IsReceived) (struct _AT91S_Pipe *pPipe, char const *pVoid);
} AT91S_Pipe;

//AT91S_Buff
typedef struct _AT91S_SBuffer
{
AT91S_Buffer parent;
char *pRdBuffer;
char const *pWrBuffer;
unsigned int szRdBuffer;
unsigned int szWrBuffer;
unsigned int stRdBuffer;
unsigned int stWrBuffer;
} AT91S_SBuffer;

// AT91S_SvcTempo
typedef struct _AT91S_SvcTempo
{

// Methods:
AT91S_TempoStatus (*Start) (
struct _AT91S_SvcTempo *pSvc,
unsigned int timeout,
unsigned int reload,
void (*callback) (AT91S_TempoStatus, void *),
void *pData);
AT91S_TempoStatus (*Stop) (struct _AT91S_SvcTempo *pSvc);

struct _AT91S_SvcTempo *pPreviousTempo;
struct _AT91S_SvcTempo *pNextTempo;

// Data
unsigned int TickTempo; //* timeout value
unsigned int ReloadTempo;//* Reload value for periodic execution
void (*TempoCallback)(AT91S_TempoStatus, void *);
void *pPrivateData;
AT91E_SvcTempo flag;
} AT91S_SvcTempo;

// AT91S_CtrlTempo
typedef struct _AT91S_CtlTempo
{
// Members:

// Start and stop for Timer hardware
AT91S_TempoStatus (*CtlTempoStart) (void *pTimer);
AT91S_TempoStatus (*CtlTempoStop) (void *pTimer);

// Start and stop for Tempo service
AT91S_TempoStatus (*SvcTempoStart) (
struct _AT91S_SvcTempo *pSvc,
unsigned int timeout,
unsigned int reload,
void (*callback) (AT91S_TempoStatus, void *),
void *pData);
AT91S_TempoStatus (*SvcTempoStop) (struct _AT91S_SvcTempo *pSvc);
AT91S_TempoStatus (*CtlTempoSetTime)(struct _AT91S_CtlTempo *pCtrl, unsigned int NewTime);
AT91S_TempoStatus (*CtlTempoGetTime)(struct _AT91S_CtlTempo *pCtrl);
AT91S_TempoStatus (*CtlTempoIsStart)(struct _AT91S_CtlTempo *pCtrl);
AT91S_TempoStatus (*CtlTempoCreate) (struct _AT91S_CtlTempo *pCtrl,struct _AT91S_SvcTempo *pTempo);
AT91S_TempoStatus (*CtlTempoRemove) (struct _AT91S_CtlTempo *pCtrl,struct _AT91S_SvcTempo *pTempo);
AT91S_TempoStatus (*CtlTempoTick) (struct _AT91S_CtlTempo *pCtrl);

// Data:

void *pPrivateData; // Pointer to devived class
void const *pTimer; // hardware
AT91PS_SvcTempo pFirstTempo;
AT91PS_SvcTempo pNewTempo;
} AT91S_CtlTempo;



//以下代码是上面几个对象的使用范例,通过这样就可以完成Host端和Targe端之间的xmodem通讯,并可以下载代码了。

AT91S_RomBoot const *pAT91;
AT91S_SBuffer sXmBuffer;
AT91S_SvcXmodem svcXmodem;
AT91S_Pipe xmodemPipe;
AT91S_CtlTempo ctlTempo;

AT91PS_Buffer pXmBuffer;
AT91PS_SvcComm pSvcXmodem;
unsigned int SizeDownloaded;

/* Init of ROM services structure */
pAT91 = AT91C_ROM_BOOT_ADDRESS;//这里取得内部ROM服务的入口地址

/* Tempo Initialization */
pAT91->OpenCtlTempo(&ctlTempo, (void *) &(pAT91->SYSTIMER_DESC));
ctlTempo.CtlTempoStart((void *) &(pAT91->SYSTIMER_DESC));

/* Xmodem Initialization */
pXmBuffer = pAT91->OpenSBuffer(&sXmBuffer);
pSvcXmodem = pAT91->OpenSvcXmodem(&svcXmodem, (AT91PS_USART)AT91C_BASE_DBGU, &ctlTempo);
pAT91->OpenPipe(&xmodemPipe, pSvcXmodem, pXmBuffer);
xmodemPipe.Read(&xmodemPipe, (char *)AT91C_UBOOT_BASE_ADDRESS, AT91C_UBOOT_MAXSIZE,
AT91F_XmodemProtocol, 0);
while(XmodemComplete !=1);



//上面部分主要针对at91rm9200片内启动时我们可以使用的片内接口服务介绍,玩H9200的朋友可以参考一下便知道缘由。

下面主要介绍at91rm9200片外启动时所使用的bootloader-->u-boot.

一. bootloader
BootLoader(引导装载程序)是嵌入式系统软件开发的非常重要的环节,它把操作系统和硬件平台衔接在一起,
是跟硬件体系密切相关的。



1.1 典型的嵌入式系统软件部分Image memory layout : bootloader , bootloader param, kernel, rootfs.

1.2 引导模式 : 1. bootstrap或download
2. autoboot
1.3 u-boot简介 :
u-boot是由Wolfgang Denk开发,它支持(mips, ppc, arm, x86)等目标体系,
可以在http://sourceforge.net 上下载获得源码,

1.4 u-boot源代码目录结构

board:开发板相关的源码,不同的板子对应一个子目录,内部放着主板相关代码。

at91rm9200dk/at91rm9200.c, config.mk, Makefile, flash.c ,u-boot.lds等都和具体开发板的硬件和地址分配有关。

common:与体系结构无关的代码文件,实现了u-boot所有命令,
其中内置了一个shell脚本解释器(hush.c, a prototype Bourne shell grammar parser), busybox中也使用了它.


cpu:与cpu相关代码文件,其中的所有子目录都是以u-boot所支持的cpu命名.

at91rm9200/at45.c, at91rm9200_ether.c, cpu.c, interrupts.c serial.c, start.S, config.mk, Makefile等.
其中cpu.c负责初始化CPU、设置指令Cache和数据Cache等;

interrupt.c负责设置系统的各种中断和异常,比如快速中断、开关中断、时钟中断、软件中断、
预取中止和未定义指令等;

start.S负责u-boot启动时执行的第一个文件,它主要是设置系统堆栈和工作方式,为跳转到C程序入口点.

disk:设备分区处理代码。

doc:u-boot相关文档。


drivers:u-boot所支持的设备驱动代码, 网卡、支持CFI的Flash、串口和USB总线等。

fs: u-boot所支持支持文件系统访问存取代码, 如jffs2.

include:u-boot head文件,主要是与各种硬件平台相关的头文件,
如include/asm-arm/arch-at91rm9200/, include/asm-arm/proc-armv

net:与网络有关的代码,BOOTP协议、TFTP协议、RARP协议代码实现.

lib_arm:与arm体系相关的代码。(这里我们主要面向的是ARM体系,所以该目录是我们主要研究对象)

tools:编译后会生成mkimage工具,用来对生成的raw bin文件加入u-boot特定的image_header.


1.5 u-boot的功能介绍


 u-boot支持SCC/FEC以太网、OOTP/TFTP引导、IP和MAC的功能.

读写Flash、DOC、IDE、IIC、EEROM、RTC

支持串行口kermit和S-record下载代码, 并直接从串口下载并执行。

在我们生成的内核镜像时,要做如下处理.
1. arm-linux-objcopy -O binary -R.note -R.comment -S vmlinux linux.bin
2. gzip -9 linux.bin
3. mkimage -A arm -O linux -T kernel -C gzip -a 0xc0008000 -e 0xc0008000 -n
"Linux-2.4.19-rmk7” -d linux.bin.gz uImage

即在Linux内核镜像vmLinux前添加了一个特殊的头,这个头在include/image.h中定义,
typedef struct image_header
{
uint32_t ih_magic; /* Image Header Magic Number */
uint32_t ih_hcrc; /* Image Header CRC Checksum */
uint32_t ih_time; /* Image Creation Timestamp */
uint32_t ih_size; /* Image Data Size */
uint32_t ih_load; /* Data Load Address */
uint32_t ih_ep; /* Entry Point Address */
uint32_t ih_dcrc; /* Image Data CRC Checksum */
uint8_t ih_os; /* Operating System */
uint8_t ih_arch; /* CPU architecture */
uint8_t ih_type; /* Image Type */
uint8_t ih_comp; /* Compression Type */
uint8_t ih_name[IH_NMLEN]; /* Image Name */
} image_header_t;

当u-boot引导时会对这个文件头进行CRC校验,如果正确,才会跳到内核执行.

如果u-boot启动以后会出现
u-boot>
敲入help, 会出现大量的命令提示,Monitor command
go - start application at address ‘addr‘
run - run commands in an environment variable
bootm - boot application image from memory
bootp - boot image via network using BootP/TFTP protocol
tftpboot- boot image via network using TFTP protocol
and env variables "ipaddr" and "serverip"
(and eventually "gatewayip")
rarpboot- boot image via network using RARP/TFTP protocol
diskboot- boot from IDE devicebootd - boot default, i.e., run ‘bootcmd‘
loads - load S-Record file over serial line
loadb - load binary file over serial line (kermit mode)
md - memory display
mm - memory modify (auto-incrementing)
nm - memory modify (constant address)
mw - memory write (fill)
cp - memory copy
cmp - memory compare
crc32 - checksum calculation
imd - i2c memory display
imm - i2c memory modify (auto-incrementing)
inm - i2c memory modify (constant address)
imw - i2c memory write (fill)
icrc32 - i2c checksum calculation
iprobe - probe to discover valid I2C chip addresses
iloop - infinite loop on address range
isdram - print SDRAM configuration information
sspi - SPI utility commands
base - print or set address offset
printenv- print environment variables
setenv - set environment variables
saveenv - save environment variables to persistent storage
protect - enable or disable FLASH write protection
erase - erase FLASH memory
flinfo - print FLASH memory information
bdinfo - print Board Info structure
iminfo - print header information for application image
coninfo - print console devices and informations
ide - IDE sub-system
loop - infinite loop on address range
mtest - simple RAM test
icache - enable or disable instruction cache
dcache - enable or disable data cache
reset - Perform RESET of the CPU
echo - echo args to console
version - print monitor version
help - print online help
- alias for ‘help‘

u-boot支持大量的命令可用, 这里就不作介绍,大家有兴趣可以看看u-boot 的README文档
3.3 对u-boot-1.0.0的修改和移植

1.6 关于u-boot的移植如下,由于u-boot的软件设计体系非常清晰,它的移植工作并不复杂,
相信各位的代码阅读功力不错的话,参照如下就可以完成。

If the system board that you have is not listed, then you will need
to port U-Boot to your hardware platform. To do this, follow these
steps:

1. Add a new configuration option for your board to the toplevel
"Makefile" and to the "MAKEALL" script, using the existing
entries as examples. Note that here and at many other places
boards and other names are listed in alphabetical sort order. Please
keep this order.

2. Create a new directory to hold your board specific code. Add any
files you need. In your board directory, you will need at least
the "Makefile", a ".c", "flash.c" and "u-boot.lds".

3. Create a new configuration file "include/configs/.h" for
your board

4. If you‘re porting U-Boot to a new CPU, then also create a new
directory to hold your CPU specific code. Add any files you need.

5. Run "make _config" with your new name.

6. Type "make", and you should get a working "u-boot.srec" file

7. Debug and solve any problems that might arise.
[Of course, this last step is much harder than it sounds.]

为了使u-boot-1.0.0支持新的开发板,一种简便的做法是在u-boot已经支持的开发板中参考选择一种较接近板的进行修改,
幸运的是在u-boot-1.0.0中已经有了at91rm9200的支持。

1.7 与at91rm9200相关的u-boot代码

在include/configs/at91rm9200dk.h 它包括开发板的CPU、系统时钟、RAM、Flash系统及其它相关的配置信息。
在include/asm-arm/AT91RM9200.h, 该文件描述了H9200寄存器的结构及若干宏定义。
具体内容要参考相关处理器手册。
在cpu/at91rm9200/目录下别为cpu.c、interrupts.c和serial.c等文件.
在board/at91rm9200dk/目录下分别为flash.c、at91rm9200dk.c, config.mk, Makefile,u-boot.lds

flash.c : u-boot读、写和删除Flash设备的源代码文件。由于不同开发板中Flash存储器的种类各不相同,
所以,修改flash.c时需参考相应的Flash芯片手册。它包括如下几个函数:
unsigned long flash_init (void ),Flash初始化;
void flash_print_info (flash_info_t *info),打印Flash信息;
int flash_erase (flash_info_t *info, int s_first, int s_last),Flash擦除;
volatile static int write_dword (flash_info_t *info, ulong dest, ulong data),Flash写入;
int write_buff (flash_info_t *info, uchar *src, ulong addr, ulong cnt),从内存复制数据。

u-boot.lds :linker scripte, 设置u-boot中各个目标文件的连接地址.

网口设备控制程序

  在drivers/目录中网口设备控制程序cs8900, bcm570x等, 还可以添加其他网卡驱动
int eth_init (bd_t *bd) : 初始化网络设备;
void eth_halt (void) : 关闭网络设备;
int eth_send (volatile void *packet,int len) : 发送数据包;
int eth_rx (void) : 接收数据包。


Makefile

  在u-boot-1.0.0/Makefile中
at91rm9200dk_config : unconfig
./mkconfig $(@:_config=) arm at91rm9200 at91rm9200dk

1.8 编译u-boot

  make at91rm9200_config
Configuring for at91rm9200 board...
make all
生成三个文件:u-boot.bin, u-boot, u-boot.srec

u-boot.bin is a raw binary image
u-boot is an image in ELF binary format
u-boot.srec is in Motorola S-Record format (objcopy -O srec -R.note -R.comment -S [inputfile] [outfile]


以上工作完成我们可以通过串口将u-boot.bin下载到主板的SDRAM中,它会自动执行, 并出现uboot>
这里我们可以通过串口把boot.bin, u-boot.bin.gz下载到主板,再用u-boot的提供的写flash功能分别
把boot.bin, u-boot.bin.gz写入到flash中,完成以上工作后,对主板跳线选择片外启动,
板子复位后会自动启动u-boot.




二.loader.bin, boot.bin, u-boot.bin代码执行流分析.

以上三个文件时at91rm9200启动所需要的三个bin,他们的实现代码并不难。
如果是你是采用at91rm9200的评估版,应该能得到其源码。

2.1 loader.bin 执行流程,这个文件主要在片内启动从串口下载代码时会用到
loader/entry.S init cpu
b main ---> crt0.S
--> copydata --> clearbss --> b boot
main.c --> boot -->
/*Get internel rom service address*/
/* Init of ROM services structure */
pAT91 = AT91C_ROM_BOOT_ADDRESS;

/* Xmodem Initialization */
--> pAT91->OpenSBuffer
--> pAT91->OpenSvcXmodem
/* System Timer initialization */
---> AT91F_AIC_ConfigureIt
/* Enable ST interrupt */
AT91F_AIC_EnableIt
AT91F_DBGU_Printk("XMODEM: Download U-BOOT ");

Jump.S
// Jump to Uboot BaseAddr exec
Jump((unsigned int)AT91C_UBOOT_BASE_ADDRESS)



2.2 boot.bin执行流程 该文件会在从片内启动时被下载到板子上,以后还会被烧写到片外Flash中,以便在片外启动时
用它来引导并解压u-boot.gz,并跳转到u-boot来执行。
boot/entry.S
b main --> crt0.S --> copydata --> clearbss --> b boot

T91F_DBGU_Printk(" ");
AT91F_DBGU_Printk("************************************** ");
AT91F_DBGU_Printk("** Welcome to at91rm9200 ** ");
AT91F_DBGU_Printk("************************************** ");

boot/misc.s /* unzip uboot.bin.gz */
----> decompress_image(SRC,DST,LEN) --> gunzip

//jump to ubootBaseAddr exec 这里跳转到解压u-boot.gz的地址处直接开始执行u-boot
asm("mov pc,%0" : : "r" (DST));

2.3 uboot.bin执行流程
u-boot/cpu/at91rm9200/start.S
start --->reset
---> copyex ---> cpu_init_crit
---> /* set up the stack */ --> start_armboot
u-boot/lib_arm/board.c

init_fnc_t *init_sequence[] = {
cpu_init, /* basic cpu dependent setup */
board_init, /* basic board dependent setup */
interrupt_init, /* set up exceptions */
env_init, /* initialize environment */
init_baudrate, /* initialze baudrate settings */
serial_init, /* serial communications setup */
console_init_f, /* stage 1 init of console */
display_banner, /* say that we are here */
dram_init, /* configure available RAM banks */
display_dram_config,
checkboard,
NULL,
};

---> start_armboot ---> call init_sequence
---> flash_init --> display_flash_config
---> nand_init ---> AT91F_DataflashInit
---> dataflash_print_info --> env_relocate
---> drv_vfd_init --> devices_init --> jumptable_init
---> console_init_r --> misc_init_r --> enable_interrupts
---> cs8900_get_enetaddr --> board_post_init -->

u-boot/common/main.c
for (;;)
{ /* shell parser */
main_loop () --> u_boot_hush_start --> readline
--> abortboot
-->printf("Hit any key to stop autoboot: %2d ", bootdelay);
}


以上是at91rm9200启动并进入u-boot的执行流分析。后面u-boot还会将uImage解压到特定的位置并开始执行内核代码。


三. 综述
总之, 不同厂商的出的Soc片子在启动方式大都提供片内和片外启动两种方式,一般都是在片内固化一段小程序
方便于程序开发而已,在其DataSheet文档中有详尽的描述。若是对at92rm9200有兴趣或玩过的朋友,可以与我共同探讨相互学习。‘

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