mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-26 22:52:18 +00:00
38 lines
1.5 KiB
Text
38 lines
1.5 KiB
Text
|
|
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.
|
|
|
|
To ensure that the linker does not discard these symbols when linking
|
|
full U-Boot we generate a list of all the commands we have built (based
|
|
on the sections mentioned above) and use that to force the linker to
|
|
first enter the symbol as undefined in the output object so that there
|
|
is then a need for the symbol to be kept (this is the UNDEF_SYM logic in
|
|
the Makefile).
|
|
|
|
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 = .;
|