mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-19 03:08:31 +00:00
38 lines
1.5 KiB
Text
38 lines
1.5 KiB
Text
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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
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to fill in a cmd_tbl_t struct.
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U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help")
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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
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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 *[]);
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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 (__u_boot_cmd_)
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and placed by the linker in a special section.
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This makes it possible for the final link to extract all commands
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compiled into any object code and construct a static array so the
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command can be found in an array starting at __u_boot_cmd_start.
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To ensure that the linker does not discard these symbols when linking
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full U-Boot we generate a list of all the commands we have built (based
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on the sections mentioned above) and use that to force the linker to
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first enter the symbol as undefined in the output object so that there
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is then a need for the symbol to be kept (this is the UNDEF_SYM logic in
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the Makefile).
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If a new board is defined do not forget to define the command section
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by writing in u-boot.lds ($(TOPDIR)/board/boardname/u-boot.lds) these
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3 lines:
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__u_boot_cmd_start = .;
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.u_boot_cmd : { *(.u_boot_cmd) }
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__u_boot_cmd_end = .;
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