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。