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", CMD_NAME);
		return ERROR_COMMAND_SYNTAX_ERROR;
	}
	if (1 == CMD_ARGC)
	{
		*sep = ", ";
		*name = CMD_ARGV[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

static const struct command_registration hello_command_handlers[] = {
	{
		.name = "hello",
		.mode = COMMAND_ANY,
		.handler = &handle_hello_command,
		.help = "print a warm greetings",
		.usage = "[<name>]",
	},
	{
		.chain = foo_command_handlers,
	}
	COMMAND_REGISTRATION_DONE
};

int hello_register_commands(struct command_context_s *cmd_ctx)
{
	return register_commands(cmd_ctx, NULL, handle_command_handlers);
}
@endcode

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

@section primercmdchain Command Chaining

This example also shows how to chain command handler registration, so
your modules can "inherit" commands provided by other (sub)modules.
Here, the hello module includes the foo commands in the same context
that the 'hello' command will be registered.

If the @c chain field had been put in the 'hello' command, then the
@c foo module commands would be registered under it.  Indeed, that
technique is used to define the 'foo bar' and 'foo baz' commands,
as well as for the example drivers that use these modules.

The code for the 'foo' command handlers can be found in @c hello.c.

@section primercmdcode Trying These Example Commands

These commands have been inherited by the dummy interface, faux flash,
and testee target drivers.  The easiest way to test these is by using the
dummy interface.

Once OpenOCD has been built with this example code, the following command
demonstrates the abilities that the @c hello module provides:
@code
openocd -c 'interface dummy' \
	-c 'dummy hello' \
	-c 'dummy hello World' \
	-c 'dummy hello {John Doe}' \
	-c 'dummy 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 displaying the help text and
exiting:
@code
Greetings!
Greetings, World!
Greetings, John Doe!
Error: hello: too many arguments
Runtime error, file "openocd.cfg", line 14:
    hello: too many arguments
dummy hello [<name>]
      prints a warm welcome
@endcode

 */