U-Boot启动引导内核分析(三)

标签：ARM bootloader U-Boot 代码分析 抵岸科技

do_bootm_linux()函数位于lib_arm/Bootm.c文件中，主要流程分析如下：

void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
bootm_headers_t *images)
{
ulong initrd_start, initrd_end;
ulong ep = 0;
bd_t *bd = gd->bd;
char *s;
int machid = bd->bi_arch_number;
void (*theKernel)(int zero, int arch, uint params);
int ret;

#ifdef CONFIG_CMDLINE_TAG
char *commandline = getenv ("bootargs");
#endif

/* find kernel entry point */
if (images->legacy_hdr_valid) {
ep = image_get_ep (&images->legacy_hdr_os_copy);
#if defined(CONFIG_FIT)
} else if (images->fit_uname_os) {
ret = fit_image_get_entry (images->fit_hdr_os,
images->fit_noffset_os, &ep);
if (ret) {
puts ("Can't get entry point property!/n");
goto error;
}
#endif
} else {
puts ("Could not find kernel entry point!/n");
goto error;
}
theKernel = (void (*)(int, int, uint))ep;

s = getenv ("machid");
if (s) {
machid = simple_strtoul (s, NULL, 16);
printf ("Using machid 0x%x from environment/n", machid);
}

ret = boot_get_ramdisk (argc, argv, images, IH_ARCH_ARM,
&initrd_start, &initrd_end);
if (ret)
goto error;

show_boot_progress (15);

debug ("## Transferring control to Linux (at address %08lx) .../n",
(ulong) theKernel);

#if defined (CONFIG_SETUP_MEMORY_TAGS) || /
defined (CONFIG_CMDLINE_TAG) || /
defined (CONFIG_INITRD_TAG) || /
defined (CONFIG_SERIAL_TAG) || /
defined (CONFIG_REVISION_TAG) || /
defined (CONFIG_LCD) || /
defined (CONFIG_VFD)
/* 初始化TAG结构体开始 */
setup_start_tag (bd);
#ifdef CONFIG_SERIAL_TAG
setup_serial_tag (¶ms);
#endif
#ifdef CONFIG_REVISION_TAG
setup_revision_tag (¶ms);
#endif
#ifdef CONFIG_SETUP_MEMORY_TAGS
/* 设置RAM参数 */
setup_memory_tags (bd);
#endif
#ifdef CONFIG_CMDLINE_TAG
setup_commandline_tag (bd, commandline);
#endif
#ifdef CONFIG_INITRD_TAG
if (initrd_start && initrd_end)
setup_initrd_tag (bd, initrd_start, initrd_end);
#endif
#if defined (CONFIG_VFD) || defined (CONFIG_LCD)
setup_videolfb_tag ((gd_t *) gd);
#endif
/* 初始化TAG结构体结束 */
setup_end_tag (bd);
#endif

/* we assume that the kernel is in place */
printf ("/nStarting kernel .../n/n");

#ifdef CONFIG_USB_DEVICE
{
extern void udc_disconnect (void);
udc_disconnect ();
}
#endif

cleanup_before_linux ();

/* 将控制权交给内核，让内核自解压启动 */
/* 传给KERNEL的参数：（struct tag *）bd->bi_boot_params */
/* 在board/atmel/at91sam9g20ek/At91sam9g20ek.c文件中有如下定义：
gd->bd->bi_boot_params = PHYS_SDRAM + 0x100;(PHYS_SDRAM = 0x20000000)
*/
theKernel (0, machid, bd->bi_boot_params);
/* does not return */
return;

error:
do_reset (cmdtp, flag, argc, argv);
return;
}

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V1.0 抵岸科技 2010-7-20 首发