Книга: Embedded Linux Primer: A Practical, Real-World Approach

7.3.2. U-Boot Command Sets

7.3.2. U-Boot Command Sets

U-Boot supports more than 60 standard command sets that enable more than 150 unique commands using CFG_* macros. A command set is enabled in U-Boot through the use of configuration setting (CFG_*) macros. For a complete list from a recent U-Boot snapshot, consult Appendix B, "U-Boot Configurable Commands." Here are just a few, to give you an idea of the capabilities available:

Command Set Commands
CFG_CMD_FLASH Flash memory commands
CFG_CMD_MEMORY Memory dump, fill, copy, compare, and so on
CFG_CMD_DHCP DHCP Support
CFG_CMD_PING Ping support
CFG_CMD_EXT2 EXT2 File system support

The following line of Listing 7-4 defines the commands enabled in a given U-Boot configuration, as driven by the board-specific header file:

#define CONFIG_COMMANDS (CONFIG_CMD_DFL | CFG_CMD_DHCP)

Instead of typing out each individual CFG_* macro in your own board-specific configuration header, you can start from a default set of commands predefined in the U-Boot source. The macro CONFIG_CMD_DFL defines this default set of commands. CONFIG_CMD_DFL specifies a list of default U-Boot command sets such as tftpboot (boot an image from a tftpserver), bootm (boot an image from memory), memory utilities such as md (display memory), and so on. To enable your specific combination of commands, you can start with the default and add and subtract as necessary. The example from Listing 7-4 adds the DHCP command set to the default. You can subtract in a similar fashion:

#define CONFIG_COMMANDS (CONFIG_CMD_DFL & ~CFG_CMD_NFS)

Take a look at any board-configuration header file in .../include/configs/ for examples.

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