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doc/README.commands
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Commands are added to U-Boot by creating a new command structure. |
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This is done by first including command.h, then using the U_BOOT_CMD() macro to fill in a cmd_tbl_t struct. |
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U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help") name: is the name of the commad. THIS IS NOT a string. |
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maxargs: the maximum number of arguments this function takes repeatable: either 0 or 1 to indicate if autorepeat is allowed |
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command: Function pointer (*cmd)(struct cmd_tbl_s *, int, int, char *[]); usage: Short description. This is a string |
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help: Long description. This is a string |
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**** Behind the scene ****** |
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The structure created is named with a special prefix and placed by the linker in a special section using the linker lists mechanism (see include/linker_lists.h) |
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This makes it possible for the final link to extract all commands compiled into any object code and construct a static array so the |
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command array can be iterated over using the linker lists macros. |
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The linker lists feature ensures that the linker does not discard these symbols when linking full U-Boot even though they are not referenced in the source code as such. |
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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: |
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.u_boot_list : { |
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KEEP(*(SORT(.u_boot_list*))); |
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} |