tcl/target/nrf52: Use 'error' instead of 'echo'

[openocd.git] / doc / manual / style.txt

/** @page styleguide Style Guides

The goals for each of these guides are:
- to produce correct code that appears clean, consistent, and readable,
- to allow developers to create patches that conform to a standard, and
- to eliminate these issues as points of future contention.

Some of these rules may be ignored in the spirit of these stated goals;
however, such exceptions should be fairly rare.

The following style guides describe a formatting, naming, and other
conventions that should be followed when writing or changing the OpenOCD
code:

- @subpage styletcl
- @subpage stylec
- @subpage styleperl
- @subpage styleautotools

In addition, the following style guides provide information for
providing documentation, either as part of the C code or stand-alone.

- @subpage styledoxygen
- @subpage styletexinfo
- @subpage stylelatex

Feedback would be welcome to improve the OpenOCD guidelines.

 */
/** @page styletcl TCL Style Guide

OpenOCD needs to expand its Jim/TCL Style Guide.

Many of the guidelines listed on the @ref stylec page should apply to
OpenOCD's Jim/TCL code as well.

 */
/** @page stylec C Style Guide

This page contains guidelines for writing new C source code for the
OpenOCD project.

@section styleformat Formatting Guide

- remove any trailing white space at the end of lines.
- use TAB characters for indentation; do NOT use spaces.
- displayed TAB width is 4 characters.
- use Unix line endings ('\\n'); do NOT use DOS endings ('\\r\\n')
- limit adjacent empty lines to at most two (2).
- remove any trailing empty lines at the end of source files
- do not "comment out" code from the tree nor put it within a block
  @code
  #if 0
  ...
  #endif
  @endcode
  otherwise it would never be checked at compile time and when new
  patches get merged it could be not compilable anymore.
  Code that is not fully working nor ready for submission should
  instead be removed entirely (git can retrieve the old version).
  For exceptional cases that require keeping some unused code, let
  the compiler check it by putting it in a block
  @code
  if (false) {
      /* explain why this code should be kept here */
      ...
  }
  @endcode
- in a @c switch statement align the @c switch with the @c case label
  @code
  switch (dev_id) {
  case 0x0123:
      size = 0x10000;
      break;
  case 0x0412:
      size = 0x20000;
      break;
  default:
      size = 0x40000;
      break;
  }
  @endcode
- in an <tt> if / then / else </tt> statement, if only one of the conditions
  require curly brackets due to multi-statement block, put the curly brackets
  also to the other condition
  @code
  if (x > 0)
      a = 12 + x;
  else
      a = 24;
  @endcode
  @code
  if (x > 0) {
      a = 12 + x;
  } else {
      a = 24;
      x = 0;
  }
  @endcode
- on <tt> if </tt> statements where the condition is split among multiple
  lines, increase the indentation of the condition to prevent it to match
  to the indentation of the <tt> then </tt> block due to length of 'if ('
  being same of the TAB width of 4 characters. Use:
  @code
  if (CMD_ARGC < 3
          || CMD_ARGC > 8)
      return ERROR_COMMAND_SYNTAX_ERROR;
  @endcode
  instead of:
  @code
  if (CMD_ARGC < 3 ||
      CMD_ARGC > 8)
      return ERROR_COMMAND_SYNTAX_ERROR;
  @endcode

Finally, try to avoid lines of code that are longer than 72-80 columns:

- long lines frequently indicate other style problems:
  - insufficient use of static functions, macros, or temporary variables
  - poor flow-control structure; "inverted" logical tests
- a few lines may be wider than this limit (typically format strings), but:
  - all C compilers will concatenate series of string constants.
  - all long string constants should be split across multiple lines.
  - do never exceed 120 columns.

@section stylenames Naming Rules

- most identifiers must use lower-case letters (and digits) only.
  - macros and enumerators must use upper-case letters (and digits) only.
  - OpenOCD identifiers should NEVER use @c MixedCaps, aka @c CamelCase.
- @c typedef names must end with the '_t' suffix.
  - This should be reserved for types that should be passed by value.
  - Do @b not mix the typedef keyword with @c struct.
- use underline characters between consecutive words in identifiers
  (e.g. @c more_than_one_word).

@section style_include_guards Include Guards

Every header file should have a unique include guard to prevent multiple
inclusion.
To guarantee uniqueness, an include guard should be based on the filename and
the full path in the project source tree.

For the header file src/helper/jim-nvp.h, the include guard would look like
this:

@code
#ifndef OPENOCD_HELPER_JIM_NVP_H
#define OPENOCD_HELPER_JIM_NVP_H

/* Your code here. */

#endif /* OPENOCD_HELPER_JIM_NVP_H */
@endcode

@section stylec99 C99 Rules

- inline functions
- @c // comments -- in new code, prefer these for single-line comments
- trailing comma allowed in enum declarations
- designated initializers ( .field = value )
- variables declarations should occur at the point of first use
- new block scopes for selection and iteration statements
- use malloc() to create dynamic arrays. Do @b not use @c alloca
or variable length arrays on the stack. non-MMU hosts(uClinux) and
pthreads require modest and predictable stack usage.

@section styletypes Type Guidelines
- use native types (@c int or <tt> unsigned int </tt>) if the type is not important
  - if size matters, use the types from \<stdint.h\> or \<inttypes.h\>:
    - @c int8_t, @c int16_t, @c int32_t, or @c int64_t: signed types of specified size
    - @c uint8_t, @c uint16_t, @c uint32_t, or @c uint64_t: unsigned types of specified size
    - use the associated @c printf and @c scanf formatting strings for these types
      (e.g. @c PRId8, PRIx16, SCNu8, ...)
  - do @b NOT redefine @c uN types from "types.h"
  - use type @c target_addr_t for target's address values
  - prefer type <tt> unsigned int </tt> to type @c unsigned

@section stylefunc Functions

- static inline functions should be preferred over macros:
@code
/* do NOT define macro-like functions like this... */
#define CUBE(x) ((x) * (x) * (x))
/* instead, define the same expression using a C99 inline function */
static inline int cube(int x) { return x * x * x; }
@endcode
- Functions should be declared static unless required by other modules
  - define static functions before first usage to avoid forward declarations.
- Functions should have no space between its name and its parameter list:
@code
int f(int x1, int x2)
{
        ...
        int y = f(x1, x2 - x1);
        ...
}
@endcode
- Separate assignment and logical test statements.  In other words, you
should write statements like the following:
@code
// separate statements should be preferred
result = foo();
if (result != ERROR_OK)
        ...
@endcode
More directly, do @b not combine these kinds of statements:
@code
// Combined statements should be avoided
if ((result = foo()) != ERROR_OK)
        return result;
@endcode
- Do not compare @c bool values with @c true or @c false but use the
  value directly
@code
if (!is_enabled)
    ...
@endcode
- Avoid comparing pointers with @c NULL
@code
buf = malloc(buf_size);
if (!buf) {
    LOG_ERROR("Out of memory");
    return ERROR_FAIL;
}
@endcode

 */
/** @page styledoxygen Doxygen Style Guide

The following sections provide guidelines for OpenOCD developers
who wish to write Doxygen comments in the code or this manual.
For an introduction to Doxygen documentation,
see the @ref primerdoxygen.

@section styledoxyblocks Doxygen Block Selection

Several different types of Doxygen comments can be used; often,
one style will be the most appropriate for a specific context.
The following guidelines provide developers with heuristics for
selecting an appropriate form and writing consistent documentation
comments.

-# use @c /// to for one-line documentation of instances.
-# for documentation requiring multiple lines, use a "block" style:
@verbatim
/**
 * @brief First sentence is short description.  Remaining text becomes
 * the full description block, where "empty" lines start new paragraphs.
 *
 * One can make text appear in @a italics, @b bold, @c monospace, or
 * in blocks such as the one in which this example appears in the Style
 * Guide.  See the Doxygen Manual for the full list of commands.
 *
 * @param foo For a function, describe the parameters (e.g. @a foo).
 * @returns The value(s) returned, or possible error conditions.
 */
@endverbatim
  -# The block should start on the line following the opening @c /\**.
  -# The end of the block, @c *&zwj;/, should also be on its own line.
  -# Every line in the block should have a @c '*' in-line with its start:
    - A leading space is required to align the @c '*' with the @c /\** line.
    - A single "empty" line should separate the function documentation
      from the block of parameter and return value descriptions.
    - Except to separate paragraphs of documentation, other extra
      "empty" lines should be removed from the block.
  -# Only single spaces should be used; do @b not add mid-line indentation.
-# If the total line length will be less than 72-80 columns, then
  - The @c /\**< form can be used on the same line.
  - This style should be used sparingly; the best use is for fields:
    @verbatim int field; /**< field description */ @endverbatim

@section styledoxyall Doxygen Style Guide

The following guidelines apply to all Doxygen comment blocks:

-# Use the @c '\@cmd' form for all doxygen commands (do @b not use @c '\\cmd').
-# Use symbol names such that Doxygen automatically creates links:
  -# @c function_name() can be used to reference functions
    (e.g. flash_set_dirty()).
  -# @c struct_name::member_name should be used to reference structure
    fields in the documentation (e.g. @c flash_driver::name).
  -# URLS get converted to markup automatically, without any extra effort.
  -# new pages can be linked into the hierarchy by using the @c \@subpage
    command somewhere the page(s) under which they should be linked:
  -# use @c \@ref in other contexts to create links to pages and sections.
-# Use good Doxygen mark-up:
  -# '\@a' (italics) should be used to reference parameters (e.g. <i>foo</i>).
  -# '\@b' (bold) should be used to emphasizing <b>single</b> words.
  -# '\@c' (monospace) should be used with <code>file names</code> and
  <code>code symbols</code>, so they appear visually distinct from
  surrounding text.
  -# To mark-up multiple words, the HTML alternatives must be used.
-# Two spaces should be used when nesting lists; do @b not use '\\t' in lists.
-# Code examples provided in documentation must conform to the Style Guide.

@section styledoxytext Doxygen Text Inputs

In addition to the guidelines in the preceding sections, the following
additional style guidelines should be considered when writing
documentation as part of standalone text files:

-# Text files must contain Doxygen at least one comment block:
  -# Documentation should begin in the first column (except for nested lists).
  -# Do NOT use the @c '*' convention that must be used in the source code.
-# Each file should contain at least one @c \@page block.
  -# Each new page should be listed as a \@subpage in the \@page block
  of the page that should serve as its parent.
  -# Large pages should be structure in parts using meaningful \@section
  and \@subsection commands.
-# Include a @c \@file block at the end of each Doxygen @c .txt file to
  document its contents:
  - Doxygen creates such pages for files automatically, but no content
    will appear on them for those that only contain manual pages.
  - The \@file block should provide useful meta-documentation to assist
    technical writers; typically, a list of the pages that it contains.
  - For example, the @ref styleguide exists in @c doc/manual/style.txt,
    which contains a reference back to itself.
-# The \@file and \@page commands should begin on the same line as
   the start of the Doxygen comment:
@verbatim
/** @page pagename Page Title

Documentation for the page.

 */
/** @file

This file contains the @ref pagename page.

 */
@endverbatim

For an example, the Doxygen source for this Style Guide can be found in
@c doc/manual/style.txt, alongside other parts of The Manual.

 */
/** @page styletexinfo Texinfo Style Guide

The User's Guide is there to provide two basic kinds of information.  It
is a guide for how and why to use each feature or mechanism of OpenOCD.
It is also the reference manual for all commands and options involved
in using them, including interface, flash, target, and other drivers.
At this time, it is the only documentation for end users; everything
else is addressing OpenOCD developers.

There are two key audiences for the User's Guide, both developer based.
The primary audience is developers using OpenOCD as a tool in their
work, or who may be starting to use it that way.  A secondary audience
includes developers who are supporting those users by packaging or
customizing it for their hardware, installing it as part of some software
distribution, or by evolving OpenOCD itself.  There is some crossover
between those audiences.  We encourage contributions from users as the
fundamental way to evolve and improve OpenOCD.  In particular, creating
a board or target specific configuration file is something that many
users will end up doing at some point, and we like to see such files
become part of the mainline release.

General documentation rules to remember include:

- Be concise and clear.  It's work to remove those extra words and
  sentences, but such "noise" doesn't help readers.
- Make it easy to skim and browse.  "Tell what you're going to say,
  then say it".  Help readers decide whether to dig in now, or
  leave it for later.
- Make sure the chapters flow well.  Presentations should not jump
  around, and should move easily from overview down to details.
- Avoid using the passive voice.
- Address the reader to clarify roles ("your config file", "the board you
  are debugging", etc.); "the user" (etc) is artificial.
- Use good English grammar and spelling.  Remember also that English
  will not be the first language for many readers.  Avoid complex or
  idiomatic usage that could create needless barriers.
- Use examples to highlight fundamental ideas and common idioms.
- Don't overuse list constructs.  This is not a slide presentation;
  prefer paragraphs.

When presenting features and mechanisms of OpenOCD:

- Explain key concepts before presenting commands using them.
- Tie examples to common developer tasks.
- When giving instructions, you can \@enumerate each step both
  to clearly delineate the steps, and to highlight that this is
  not explanatory text.
- When you provide "how to use it" advice or tutorials, keep it
  in separate sections from the reference material.
- Good indexing is something of a black art.  Use \@cindex for important
  concepts, but don't overuse it.  In particular, rely on the \@deffn
  indexing, and use \@cindex primarily with significant blocks of text
  such as \@subsection.  The \@dfn of a key term may merit indexing.
- Use \@xref (and \@anchor) with care.  Hardcopy versions, from the PDF,
  must make sense without clickable links (which don't work all that well
  with Texinfo in any case).  If you find you're using many links,
  read that as a symptom that the presentation may be disjointed and
  confusing.
- Avoid font tricks like \@b, but use \@option, \@file, \@dfn, \@emph
  and related mechanisms where appropriate.

For technical reference material:

- It's OK to start sections with explanations and end them with
  detailed lists of the relevant commands.
- Use the \@deffn style declarations to define all commands and drivers.
  These will automatically appear in the relevant index, and those
  declarations help promote consistent presentation and style.
   - It's a "Command" if it can be used interactively.
   - Else it's a "Config Command" if it must be used before the
     configuration stage completes.
   - For a "Driver", list its name.
   - Use EBNF style regular expressions to define parameters:
     brackets around zero-or-one choices, parentheses around
     exactly-one choices.
   - Use \@option, \@file, \@var and other mechanisms where appropriate.
   - Say what output it displays, and what value it returns to callers.
   - Explain clearly what the command does.  Sometimes you will find
     that it can't be explained clearly.  That usually means the command
     is poorly designed; replace it with something better, if you can.
   - Be complete:  document all commands, except as part of a strategy
     to phase something in or out.
   - Be correct:  review the documentation against the code, and
     vice versa.
- Alphabetize the \@defn declarations for all commands in each
  section.
- Keep the per-command documentation focused on exactly what that
  command does, not motivation, advice, suggestions, or big examples.
  When commands deserve such expanded text, it belongs elsewhere.
  Solutions might be using a \@section explaining a cluster of related
  commands, or acting as a mini-tutorial.
- Details for any given driver should be grouped together.

The User's Guide is the first place most users will start reading,
after they begin using OpenOCD.  Make that investment of their time
be as productive as possible.  Needing to look at OpenOCD source code,
to figure out how to use it is a bad sign, though it's OK to need to
look at the User's guide to figure out what a config script is doing.

 */
/** @page stylelatex LaTeX Style Guide

This page needs to provide style guidelines for using LaTeX, the
typesetting language used by The References for OpenOCD Hardware.
Likewise, the @ref primerlatex for using this guide needs to be completed.

 */
/** @page styleperl Perl Style Guide

This page provides some style guidelines for using Perl, a scripting
language used by several small tools in the tree:

-# Ensure all Perl scripts use the proper suffix (@c .pl for scripts, and
   @c .pm for modules)
-# Pass files as script parameters or piped as input:
  - Do NOT code paths to files in the tree, as this breaks out-of-tree builds.
  - If you must, then you must also use an automake rule to create the script.
-# use @c '#!/usr/bin/perl' as the first line of Perl scripts.
-# always <code>use strict</code> and <code>use warnings</code>
-# invoke scripts indirectly in Makefiles or other scripts:
@code
perl script.pl
@endcode

Maintainers must also be sure to follow additional guidelines:
-# Ensure that Perl scripts are committed as executables:
    Use "<code>chmod +x script.pl</code>"
    @a before using "<code>git add script.pl</code>"

 */
/** @page styleautotools Autotools Style Guide

This page contains style guidelines for the OpenOCD autotools scripts.

The following guidelines apply to the @c configure.ac file:
- Better guidelines need to be developed, but until then...
- Use good judgement.

The following guidelines apply to @c Makefile.am files:
-# When assigning variables with long lists of items:
  -# Separate the values on each line to make the files "patch friendly":
@code
VAR = \
        value1 \
        value2 \
        ...
        value9 \
        value10
@endcode
 */
/** @file

This file contains the @ref styleguide pages.  The @ref styleguide pages
include the following Style Guides for their respective code and
documentation languages:

- @ref styletcl
- @ref stylec
- @ref styledoxygen
- @ref styletexinfo
- @ref stylelatex
- @ref styleperl
- @ref styleautotools

 */