blob: 125f077c08ffc03f7cf549e6c54480e3a6a41b87 [file] [log] [blame]
wdenk0d498392003-07-01 21:06:45 +00001
2Commands are added to U-Boot by creating a new command structure.
Peter Meerwald00309c62012-02-08 05:31:52 +00003This is done by first including command.h, then using the U_BOOT_CMD() macro
4to fill in a cmd_tbl_t struct.
wdenk0d498392003-07-01 21:06:45 +00005
6U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help")
7
8name: is the name of the commad. THIS IS NOT a string.
Peter Meerwald00309c62012-02-08 05:31:52 +00009maxargs: the maximum number of arguments this function takes
10repeatable: either 0 or 1 to indicate if autorepeat is allowed
wdenk0d498392003-07-01 21:06:45 +000011command: Function pointer (*cmd)(struct cmd_tbl_s *, int, int, char *[]);
12usage: Short description. This is a string
Peter Meerwald00309c62012-02-08 05:31:52 +000013help: Long description. This is a string
wdenk0d498392003-07-01 21:06:45 +000014
15
Peter Meerwald00309c62012-02-08 05:31:52 +000016**** Behind the scene ******
wdenk0d498392003-07-01 21:06:45 +000017
18The structure created is named with a special prefix (__u_boot_cmd_)
19and placed by the linker in a special section.
20
21This makes it possible for the final link to extract all commands
22compiled into any object code and construct a static array so the
23command can be found in an array starting at __u_boot_cmd_start.
24
Tom Rini2d1d6582012-09-20 06:02:43 +000025To ensure that the linker does not discard these symbols when linking
26full U-Boot we generate a list of all the commands we have built (based
27on the sections mentioned above) and use that to force the linker to
28first enter the symbol as undefined in the output object so that there
29is then a need for the symbol to be kept (this is the UNDEF_SYM logic in
30the Makefile).
31
wdenk0d498392003-07-01 21:06:45 +000032If a new board is defined do not forget to define the command section
33by writing in u-boot.lds ($(TOPDIR)/board/boardname/u-boot.lds) these
343 lines:
35
36 __u_boot_cmd_start = .;
37 .u_boot_cmd : { *(.u_boot_cmd) }
38 __u_boot_cmd_end = .;