openocd/doc/manual/primer/commands.txt

/** @page primercommand Command Development Primer

This page provides a primer for writing commands by introducing @c hello
module.  The full source code used in this example can be found in
hello.c, and the @ref primercmdcode section shows how to use it.

A summary of this information can be found in @ref helpercommand .

@section primercmdhandler Command Handlers

Defining new commands and their helpers is easy.  The following code
defines a simple command handler that delegates its argument parsing:
@code
COMMAND_HANDLER(handle_hello_command)
{
	const char *sep, *name;
	int retval = CALL_COMMAND_HANDLER(handle_hello_args);
	if (ERROR_OK == retval)
		command_print(cmd_ctx, "Greetings%s%s!", sep, name);
	return retval;
}
@endcode

Here, the @c COMMAND_HANDLER macro establishes the function signature,
see in command.h by the @c __COMMAND_HANDLER macro.

The COMMAND_HELPER macro function allows defining functions with an
extended version of the base signature.  These helper functions can be
called (with the appropriate parameters), the @c CALL_COMMAND_HANDLER
macro to pass any e as parameters to the following helper function:

The subsequent blocks of code are a normal C function that can do
anything, so only complex commands deserve should use comamnd helper
functions.  In this respect, this example uses one to demonstrate how --
not when -- they should be used.

@code
static COMMAND_HELPER(handle_hello_args, const char **sep, const char **name)
{
	if (argc > 1)
	{
		LOG_ERROR("%s: too many arguments", COMMAND_NAME);
		return ERROR_COMMAND_SYNTAX_ERROR;
	}
	if (1 == argc)
	{
		*sep = ", ";
		*name = args[0];
	}
	else
		*sep = *name = "";

	return ERROR_OK;
}
@endcode

Of course, you may also call other macros or functions, but that extends
beyond the scope of this tutorial on writing commands. 

@section primercmdreg Command Registration

Before this new function can be used, it must be registered somehow.
For a new module, registering should be done in a new function for
the purpose, which must be called from @c openocd.c:
@code
int hello_register_commands(struct command_context_s *cmd_ctx)
{
	struct command_s *cmd = register_command(cmd_ctx, NULL, "hello",
			NULL, COMMAND_ANY, "print greetings");
	return cmd ? ERROR_OK : -ENOMEM;
}
@endcode

That's it!  The command should now be registered and avaiable to scripts.

@section primercmdcode Trying These Example Commands

The commands may be enabled by editing src/openocd.c and uncommenting
the call to @c hello_register_commands and rebuilding the source tree.

Once OpenOCD has been built with this example code, the following script
demonstrate the abilities that the @c hello module provides:
@code
hello
hello World
hello {John Doe}
hello John Doe  # error: too many arguments
@endcode

If saved in @c hello.cfg, then running <code>openocd -f hello.cfg</code>
should produce the following output before exiting:
@code
Greetings!
Greetings, World!
Greetings, John Doe!
Error: ocd_hello: too many arguments
@endcode

 */