嵌入式系统 Boot Loader 技术内幕

 
while(count) {
	*dest++ = *src++; /* they are all aligned with word boundary */
	count -= 4; /* byte number */
};

/* The list ends with an ATAG_NONE node. */
#define ATAG_NONE	0x00000000

struct tag_header {
	u32 size; /* 注意，这里size是字数为单位的 */
	u32 tag;
};
……
struct tag {
	struct tag_header hdr;
	union {
		struct tag_core		core;
		struct tag_mem32	mem;
		struct tag_videotext	videotext;
		struct tag_ramdisk	ramdisk;
		struct tag_initrd	initrd;
		struct tag_serialnr	serialnr;
		struct tag_revision	revision;
		struct tag_videolfb	videolfb;
		struct tag_cmdline	cmdline;

		/*
		 * Acorn specific
		 */
		struct tag_acorn	acorn;

		/*
		 * DC21285 specific
		 */
		struct tag_memclk	memclk;
	} u;
};

params = (struct tag *)BOOT_PARAMS;

	params->hdr.tag = ATAG_CORE;
	params->hdr.size = tag_size(tag_core);

	params->u.core.flags = 0;
	params->u.core.pagesize = 0;
	params->u.core.rootdev = 0;

	params = tag_next(params);

for(i = 0; i < NUM_MEM_AREAS; i++) {
		if(memory_map[i].used) {
			params->hdr.tag = ATAG_MEM;
			params->hdr.size = tag_size(tag_mem32);

			params->u.mem.start = memory_map[i].start;
			params->u.mem.size = memory_map[i].size;
			
			params = tag_next(params);
		}
}

char *p;

	/* eat leading white space */
	for(p = commandline; *p == ' '; p++)
		;

	/* skip non-existent command lines so the kernel will still
    * use its default command line.
	 */
	if(*p == '\0')
		return;

	params->hdr.tag = ATAG_CMDLINE;
	params->hdr.size = (sizeof(struct tag_header) + strlen(p) + 1 + 4) >> 2;

	strcpy(params->u.cmdline.cmdline, p);

	params = tag_next(params);