add documention for writing built-in commands

This documentation update provides an introduction to the command
handling facilities provided by command.[ch].  A primer walks the user
through the elements of a pointedly pedantic module: src/hello.c.

A summary of the API is provided in the OpenOCD Architecture section.
__archive__
Zachary T Welch 2009-11-11 01:31:34 -08:00
parent 89870c86e7
commit ebbc762182
3 changed files with 163 additions and 2 deletions

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@ -31,7 +31,63 @@ This section needs to be expanded to describe OpenOCD's Jim API.
/** @page helpercommand OpenOCD Command API
This section needs to be expanded to describe OpenOCD's Command API.
OpenOCD's command API allows modules to register callbacks that are then
available to the scripting services. It provides the mechanism for
these commands to be dispatched to the modlue using a standard
interfaces. It provides macros for defining functions that use and
extend this interface.
@section helpercmdhandler Command Handlers
Command handlers are functions with a particular signature, which can
be extended by modules for passing additional parameters to helpers or
another layer of handlers.
@subsection helpercmdhandlerdef Defining and Calling Command Handlers
These functions should be defined using the COMMAND_HANDLER macro.
These methods must be defined as static, as their principle entry point
should be the run_command dispatch mechanism.
Command helper functions that require access to the full set of
parameters should be defined using the COMMAND_HELPER. These must be
declared static by you, as sometimes you might want to share a helper
among several files (e.g. s3c24xx_nand.h).
Both types of routines must be called using the CALL_COMMAND_HANDLER macro.
Calls using this macro to normal handlers require the name of the command
handler (which can a name or function pointer). Calls to helpers and
derived handlers must pass those extra parameters specified by their
definitions; however, lexical capture is used for the core parameters.
This dirty trick is being used as a stop-gap measure while the API is
migrated to one that passes a pointer to a structure containing the
same ingredients. At that point, this macro will be removed and callers
will be able to use direct invocations.
Thus, the following macros can be used to define and call command
handlers or helpers:
- COMMAND_HANDLER - declare or define a command handler.
- COMMAND_HELPER - declare or define a derived command handler or helper.
- CALL_COMMAND_COMMAND - call a command handler/helper.
@subsection helpercmdhandlerparam Command Handler Parameters
The following parameters are defined in the scope of all command
handlers and helpers:
- <code>struct command_context_s *cmd_ctx</code> - the command's context
- <code>unsigned argc</code> - the number of command arguments
- <code>const char *args[]</code> - contains the command arguments
@subsection helpercmdhandlermacros Command Handler Macros
In addition, the following macro may be used:
- <code>COMMAND_NAME</code> - contains the command name
@section helpercmdprimer Command Development Primer
This @ref primercommand provides details about the @c hello module,
showing how the pieces desrcribed on this page fit together.
*/

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@ -42,11 +42,17 @@ associated with the fundamental technologies used by OpenOCD.
- @subpage primertcl
- @subpage primerjtag
These documents should bridge any "ancillary" gaps in contributor
The above documents should bridge any "ancillary" gaps in contributor
knowledge, without having to learn the complete languages or technology.
They should provide enough information for experienced developers to
learn how to make "correct" changes when creating patches.
Beyond the fundamentals, the following primers provide introductory
tutorials for OpenOCD's sub-systems. These complement the @ref oocd
pages that provide more high-level perspective on related topics.
- @subpage primercommand
In all cases, these Primers should use idiomatic conventions that the
community has agreed are the "right way of doing things". In this
respect, these documents typically assume some familiarity with the

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@ -0,0 +1,99 @@
/** @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
*/