cubieboard boot过程

A10的启动过程大概可分为5步：BootRom，SPL，Uboot，Kernel，RootFileSystem。本文只关注镜像的加载过程，分析RootRom->SPL->Uboot的启动流程。

系统上电后，ARM处理器在复位时从地址0x000000开始执行指令，把板上ROM或Flash映射到这一地址。A10将启动设备选择程序固化在CPU内部的一个32KB ROM中，默认的启动时序为SD Card0，NAND FLASH，SD Card2，SPI NOR FLASH。另外通过外部的一个启动选择引脚可以使其跳转到USB启动模式。通常情况下，启动选择引脚状态连接50K内部上拉电阻。在上电后，执行存储在ROM中的启动代码，将自动检测启动选择引脚状态。只有当该引脚状态为低电平时选择USB启动模式。

启动设备选择程序的流程图：

 

在选择启动设备后将加载并执行bootload程序，CPU通过拷贝或映射bootload程序到内存，然后执行bootload的第一条指令。通过阅读官方的uboot烧写方法，发现A10通过uboot引导系统，但却没有加载整个uboot，而是在此之前先载入了uboot SPL。什么是SPL？通过查阅uboot的官网资料得知，SPL是一个迷你版的uboot，全拼为Second Program Loader。适用于SOC的内部SROM<64K的情况，用它来加载完整的uboot程序到SDROM，并通过完整uboot加载内核来启动系统。

 

SPL程序流程如下：

1.初始化ARM处理器

2.初始化串口控制台

3.配置时钟和最基础的分频

4.初始化SDRAM

5.配置引脚多路复用功能

6.启动设备初始化（即上面选择的启动设备）

7.加载完整的uboot程序并转交控制权

 

 

搞清楚了上面的概念，可以知道Cubieboard出厂已经烧写了NandFlash中的程序，即在启动选择时使用的是NandFlash。现在根据全志A10上的步骤，我们尝试用SDC1（即Cubieboard上卡槽中的TF卡）来启动系统。

 

下载并编译uboot

#git clone https://github.com/linux-sunxi/u-boot-sunxi.git

#cd u-boot-sunxi

#export CROSS_COMPILE=arm-linux-gnueabihf-

#make cubieboard

 

为TF卡烧写引导程序

#dd if=/dev/zero of=/dev/sdb bs=1M count=1 # 清空SD卡（包括分区表）

尝试不建立分区表，直接烧写引导程序，无法启动系统。

因此按需求给TF卡分区，我只创建了唯一一个200M主分区，此处不详述分区过程，下面是我使用的TF卡的分区表信息。

$ sudo fdisk -l /dev/sdb

Disk /dev/sdb: 1977 MB, 1977614336 bytes

52 heads, 30 sectors/track, 2475 cylinders, total 3862528 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00000000

Device Boot Start End Blocks Id System

/dev/sdb1 2048 411647 204800 83 Linux

通过A10相关资料，通过以下2条命令烧写spl和uboot到指定位置，暂时不清楚如何确定这2个读取位置。

#dd if=spl/sunxi-spl.bin of=/dev/sdb bs=1024 seek=8

#dd if=u-boot.bin of=/dev/sdb bs=1024 seek=32

 

 

烧写完成后插入TF卡到CB的卡槽中，连接USB转TTL串口线，打开串口终端，上电。

串口打印信息如下：

U -Boot SPL 2012. 10 - 04277 -g7aa9f04 (Mar 10 2013 - 00 : 36 : 40)
DRAM : 1024MB
SUNXI SD /MMC : 0


U -Boot 2012. 10 - 04277 -g7aa9f04 (Mar 10 2013 - 00 : 36 : 40) Allwinner Technology

CPU : SUNXI Family
Board : Cubieboard
I2C : ready
DRAM : 1 GiB
MMC : SUNXI SD /MMC : 0
* * * Warning - bad CRC, using default environment

In : serial
Out : serial
Err : serial
Hit any key to stop autoboot : 0

* * Unable to use mmc 0 : 1 for fatload * *
Loading file "uEnv.txt" from mmc device 0 : 1
Failed to mount ext2 filesystem...
* * Bad ext2 partition or disk - mmc 0 : 1 * *
ext2load - load binary file from a Ext2 filesystem

Usage :
ext2load <interface > <dev[ :part] > [addr] [filename] [bytes]
- load binary file 'filename' from 'dev' on 'interface'
to address 'addr' from ext2 filesystem
Loading file "boot/uEnv.txt" from mmc device 0 : 1
Failed to mount ext2 filesystem...
* * Bad ext2 partition or disk - mmc 0 : 1 * *
ext2load - load binary file from a Ext2 filesystem

Usage :
ext2load <interface > <dev[ :part] > [addr] [filename] [bytes]
- load binary file 'filename' from 'dev' on 'interface'
to address 'addr' from ext2 filesystem

* * Unable to use mmc 0 : 1 for fatload * *
Loading file "boot.scr" from mmc device 0 : 1
Failed to mount ext2 filesystem...
* * Bad ext2 partition or disk - mmc 0 : 1 * *
ext2load - load binary file from a Ext2 filesystem

Usage :
ext2load <interface > <dev[ :part] > [addr] [filename] [bytes]
- load binary file 'filename' from 'dev' on 'interface'
to address 'addr' from ext2 filesystem
Loading file "boot/boot.scr" from mmc device 0 : 1
Failed to mount ext2 filesystem...
* * Bad ext2 partition or disk - mmc 0 : 1 * *
ext2load - load binary file from a Ext2 filesystem

Usage :
ext2load <interface > <dev[ :part] > [addr] [filename] [bytes]
- load binary file 'filename' from 'dev' on 'interface'
to address 'addr' from ext2 filesystem

* * Unable to use mmc 0 : 1 for fatload * *
sun4i #

通过串口信息可以看到SPL和Uboot已经成功加载，uboot最后通过ext2load命令读取uEnv.txt和boot.scr文件失败后退回控制台。

 

下面通过源码分析SPL载入完整Uboot的过程。

/u-boot-sunxi/common/spl/spl.c - board_init_r

void board_init_r(gd_t *dummy1, ulong dummy2)
{
u32 boot_device;
debug( ">>spl:board_init_r()\n");
puts( ">>spl:board_init_r()\n");

# ifdef CONFIG_SYS_SPL_MALLOC_START
mem_malloc_init(CONFIG_SYS_SPL_MALLOC_START,
CONFIG_SYS_SPL_MALLOC_SIZE);
# endif

timer_init();

# ifdef CONFIG_SPL_BOARD_INIT
spl_board_init();
# endif

boot_device = spl_boot_device(); //检测启动设备，此处返回BOOT_DEVICE_MMC1
debug( "boot device - %d\n", boot_device);
switch (boot_device) {
# ifdef CONFIG_SPL_RAM_DEVICE
case BOOT_DEVICE_RAM :
spl_ram_load_image();
break;
# endif
# ifdef CONFIG_SPL_MMC_SUPPORT
case BOOT_DEVICE_MMC1 :
case BOOT_DEVICE_MMC2 :
case BOOT_DEVICE_MMC2_2 :
spl_mmc_load_image(); //通过mmc读取image
break;
# endif
# ifdef CONFIG_SPL_NAND_SUPPORT
case BOOT_DEVICE_NAND :
spl_nand_load_image();
break;
# endif
# ifdef CONFIG_SPL_NOR_SUPPORT
case BOOT_DEVICE_NOR :
spl_nor_load_image();
break;
# endif
# ifdef CONFIG_SPL_YMODEM_SUPPORT
case BOOT_DEVICE_UART :
spl_ymodem_load_image();
break;
# endif
# ifdef CONFIG_SPL_SPI_SUPPORT
case BOOT_DEVICE_SPI :
spl_spi_load_image();
break;
# endif
# ifdef CONFIG_SPL_ETH_SUPPORT
case BOOT_DEVICE_CPGMAC :
# ifdef CONFIG_SPL_ETH_DEVICE
spl_net_load_image(CONFIG_SPL_ETH_DEVICE);
# else
spl_net_load_image(NULL);
# endif
break;
# endif
default :
debug( "SPL: Un-supported Boot Device\n");
hang();
}

switch (spl_image.os) {
case IH_OS_U_BOOT :
debug( "Jumping to U-Boot\n");
break;
# ifdef CONFIG_SPL_OS_BOOT
case IH_OS_LINUX :
debug( "Jumping to Linux\n");
spl_board_prepare_for_linux();
jump_to_image_linux(( void *)CONFIG_SYS_SPL_ARGS_ADDR);
# endif
default :
debug( "Unsupported OS image.. Jumping nevertheless..\n");
}
jump_to_image_no_args();
}

u-boot-sunxi/arch/arm/cpu/armv7/sunxi/board.c - spl_boot_device

u32 spl_boot_device( void) {

u32 cfg;

# ifdef CONFIG_SPL_NOR_SUPPORT
/* TODO */
# endif

# ifdef CONFIG_SPL_MMC_SUPPORT
cfg = sunxi_gpio_get_cfgpin(SUNXI_GPC( 7));
if( cfg == SUNXI_GPC7_SDC2_CLK )
return BOOT_DEVICE_MMC2;
# endif

# ifdef CONFIG_SPL_NAND_SUPPORT
cfg = sunxi_gpio_get_cfgpin(SUNXI_GPC( 2));
if( cfg == SUNXI_GPC2_NCLE )
return BOOT_DEVICE_NAND;
# endif

# ifdef CONFIG_SPL_MMC_SUPPORT
cfg = sunxi_gpio_get_cfgpin(SUNXI_GPF( 2));
if( cfg == SUNXI_GPF2_SDC0_CLK )
return BOOT_DEVICE_MMC1;
# endif

/* if we are here, something goes wrong. Fall back on MMC */
return BOOT_DEVICE_MMC1;
}

启动设备是通过读取连接相应设备的GPIO状态来判断的，但在上述条件下执行该段代码时并没有成功检测到设备，直到最后返回BOOT_DEVICE_MMC1。

u-boot-sunxi/drivers/mmc/spl_mmc.c - spl_mmc_load_image

void spl_mmc_load_image( void)
{
struct mmc *mmc;
int err;
u32 boot_mode;

mmc_initialize(gd - >bd);
/* We register only one device. So, the dev id is always 0 */
mmc = find_mmc_device( 0);
if ( !mmc) {
puts( "spl: mmc device not found!!\n");
hang();
}

err = mmc_init(mmc);
if (err) {
printf( "spl: mmc init failed: err - %d\n", err);
hang();
}
boot_mode = spl_boot_mode(); // sunxi的代码在此处直接返回了MMCSD_MODE_RAW
if (boot_mode == MMCSD_MODE_RAW) {
debug( "boot mode - RAW\n");
mmc_load_image_raw(mmc);
# ifdef CONFIG_SPL_FAT_SUPPORT
} else if (boot_mode == MMCSD_MODE_FAT) {
debug( "boot mode - FAT\n");
mmc_load_image_fat(mmc);
# endif
} else {
puts( "spl: wrong MMC boot mode\n");
hang();
}
}

u-boot-sunxi/drivers/mmc/spl_mmc.c - mmc_load_image_raw

static void mmc_load_image_raw( struct mmc *mmc)
{
u32 image_size_sectors, err;
const struct image_header *header;

header = ( struct image_header *)(CONFIG_SYS_TEXT_BASE -
sizeof( struct image_header));

/* read image header to find the image size & load address */
err = mmc - >block_dev.block_read( 0,
CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR, 1,
( void *)header);

if (err < = 0)
goto end;

spl_parse_image_header(header);

/* convert size to sectors - round up */
image_size_sectors = (spl_image.size + mmc - >read_bl_len - 1) /
mmc - >read_bl_len;

/* Read the header too to avoid extra memcpy */
err = mmc - >block_dev.block_read( 0,
CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR,
image_size_sectors, ( void *)spl_image.load_addr); //此处确定了Uboot读取位置

end :
if (err < = 0) {
printf( "spl: mmc blk read err - %d\n", err);
hang();
}
}

u-boot-sunxi/include/configs/sunxi-common.h

# define CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR ( 64) /* 32KB offset */
# define CONFIG_SYS_U_BOOT_MAX_SIZE_SECTORS ( 400) /* 200KB, enough for a full u-boot.bin */

通过CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR确定了我们把完整的uboot写入到TF卡从32K位置开始。