doc/manual/primer/commands.txt

   1 /** @page primercommand Command Development Primer
   2
   3 This page provides a primer for writing commands by introducing @c hello
   4 module.  The full source code used in this example can be found in
   5 hello.c, and the @ref primercmdcode section shows how to use it.
   6
   7 A summary of this information can be found in @ref helpercommand .
   8
   9 @section primercmdhandler Command Handlers
  10
  11 Defining new commands and their helpers is easy.  The following code
  12 defines a simple command handler that delegates its argument parsing:
  13 @code
  14 COMMAND_HANDLER(handle_hello_command)
  15 {
  16         const char *sep, *name;
  17         int retval = CALL_COMMAND_HANDLER(handle_hello_args);
  18         if (ERROR_OK == retval)
  19                 command_print(CMD_CTX, "Greetings%s%s!", sep, name);
  20         return retval;
  21 }
  22 @endcode
  23
  24 Here, the @c COMMAND_HANDLER macro establishes the function signature,
  25 see in command.h by the @c __COMMAND_HANDLER macro.
  26
  27 The COMMAND_HELPER macro function allows defining functions with an
  28 extended version of the base signature.  These helper functions can be
  29 called (with the appropriate parameters), the @c CALL_COMMAND_HANDLER
  30 macro to pass any e as parameters to the following helper function:
  31
  32 The subsequent blocks of code are a normal C function that can do
  33 anything, so only complex commands deserve should use comamnd helper
  34 functions.  In this respect, this example uses one to demonstrate how --
  35 not when -- they should be used.
  36
  37 @code
  38 static COMMAND_HELPER(handle_hello_args, const char **sep, const char **name)
  39 {
  40         if (argc > 1)
  41         {
  42                 LOG_ERROR("%s: too many arguments", CMD_NAME);
  43                 return ERROR_COMMAND_SYNTAX_ERROR;
  44         }
  45         if (1 == CMD_ARGC)
  46         {
  47                 *sep = ", ";
  48                 *name = CMD_ARGV[0];
  49         }
  50         else
  51                 *sep = *name = "";
  52
  53         return ERROR_OK;
  54 }
  55 @endcode
  56
  57 Of course, you may also call other macros or functions, but that extends
  58 beyond the scope of this tutorial on writing commands.
  59
  60 @section primercmdreg Command Registration
  61
  62 Before this new function can be used, it must be registered somehow.
  63 For a new module, registering should be done in a new function for
  64 the purpose, which must be called from @c openocd.c:
  65 @code
  66
  67 static const struct command_registration hello_command_handlers[] = {
  68         {
  69                 .name = "hello",
  70                 .mode = COMMAND_ANY,
  71                 .handler = &handle_hello_command,
  72                 .help = "print a warm greetings",
  73                 .usage = "[<name>]",
  74         },
  75         {
  76                 .chain = foo_command_handlers,
  77         }
  78         COMMAND_REGISTRATION_DONE
  79 };
  80
  81 int hello_register_commands(struct command_context_s *cmd_ctx)
  82 {
  83         return register_commands(cmd_ctx, NULL, handle_command_handlers);
  84 }
  85 @endcode
  86
  87 That's it!  The command should now be registered and avaiable to scripts.
  88
  89 @section primercmdchain Command Chaining
  90
  91 This example also shows how to chain command handler registration, so
  92 your modules can "inherit" commands provided by other (sub)modules.
  93 Here, the hello module includes the foo commands in the same context
  94 that the 'hello' command will be registered.
  95
  96 If the @c chain field had been put in the 'hello' command, then the
  97 @c foo module commands would be registered under it.  Indeed, that
  98 technique is used to define the 'foo bar' and 'foo baz' commands,
  99 as well as for the example drivers that use these modules.
 100
 101 The code for the 'foo' command handlers can be found in @c hello.c.
 102
 103 @section primercmdcode Trying These Example Commands
 104
 105 These commands have been inherited by the dummy interface, faux flash,
 106 and testee target drivers.  The easiest way to test these is by using the
 107 dummy interface.
 108
 109 Once OpenOCD has been built with this example code, the following command
 110 demonstrates the abilities that the @c hello module provides:
 111 @code
 112 openocd -c 'interface dummy' \
 113         -c 'dummy hello' \
 114         -c 'dummy hello World' \
 115         -c 'dummy hello {John Doe}' \
 116         -c 'dummy hello John Doe'  # error: too many arguments
 117 @endcode
 118
 119 If saved in @c hello.cfg, then running <code>openocd -f hello.cfg</code>
 120 should produce the following output before displaying the help text and
 121 exiting:
 122 @code
 123 Greetings!
 124 Greetings, World!
 125 Greetings, John Doe!
 126 Error: hello: too many arguments
 127 Runtime error, file "openocd.cfg", line 14:
 128     hello: too many arguments
 129 dummy hello [<name>]
 130       prints a warm welcome
 131 @endcode
 132
 133  */