u-boot/doc/README.commands

Commands are added to U-Boot by creating a new command structure.
This is done by first including command.h, then using the U_BOOT_CMD() macro
to fill in a cmd_tbl_t struct.

U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help")

name:	 is the name of the commad. THIS IS NOT a string.
maxargs: the maximum number of arguments this function takes
repeatable: either 0 or 1 to indicate if autorepeat is allowed
command: Function pointer (*cmd)(struct cmd_tbl_s *, int, int, char *[]);
usage:	 Short description. This is a string
help:	 Long description. This is a string


**** Behind the scene ******

The structure created is named with a special prefix (__u_boot_cmd_)
and placed by the linker in a special section.

This makes it possible for the final link to extract all commands
compiled into any object code and construct a static array so the
command can be found in an array starting at __u_boot_cmd_start.

If a new board is defined do not forget to define the command section
by writing in u-boot.lds ($(TOPDIR)/board/boardname/u-boot.lds) these
3 lines:

	__u_boot_cmd_start = .;
	.u_boot_cmd : { *(.u_boot_cmd) }
	__u_boot_cmd_end = .;