docs/wiki/geda-hse_howto.html

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  15 <h1 class="sectionedit302"><a name="hooks_scheme_extension_howto" id="hooks_scheme_extension_howto">Hooks/Scheme Extension HOWTO</a></h1>
  16 <div class="level1">
  17 <pre class="code">gEDA - GPL Electronic Design Automation
  18
  19 HOOKS AND SCHEME EXTENSION IN GSCHEM
  20 ====================================
  21
  22 Copyright (C) 2000 Stefan Petersen
  23
  24 This program is free software; you can redistribute it and/or modify
  25 it under the terms of the GNU General Public License as published by
  26 the Free Software Foundation; either version 2 of the License, or
  27 (at your option) any later version.
  28
  29 This program is distributed in the hope that it will be useful,
  30 but WITHOUT ANY WARRANTY; without even the implied warranty of
  31 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  32 GNU General Public License for more details.
  33
  34 You should have received a copy of the GNU General Public License
  35 along with this program; if not, write to the Free Software
  36 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  37
  38
  39 Introduction
  40 ------------
  41 gschem has a scheme interpreter (called Guile) built in. Though not
  42 complete, there are extensions to this interpreter to get access to
  43 different parts of the schematic.
  44
  45 There are a couple of other scheme extensions available that will not be
  46 described here. They belong mainly to rc-files (resource files in
  47 gEDA programs are really scheme scripts) and to the keymapping system
  48 (described in separate keymapping documentation).
  49
  50 The rest I will try to describe here.
  51
  52
  53 Scheme functions
  54 ----------------
  55 There are two function available for handling attributes in the schematic.
  56
  57 * get-attribute-name-value
  58 Inparameter  : an attribute
  59 Outparameter : a pair with the name of the attribute as string in the
  60                car element and the value of the attribute in the cdr
  61                element.
  62 Description  : Simply an accessor to the information hidden in the type
  63                attribute. The functionality of this is placed in libgeda
  64                since the C-type ATTRIBUTE is defined there.
  65
  66 * set-attribute-value!
  67 Inparameter  : an attribute and a string.
  68 Outparameter : undefined.
  69 Description  : Sets a new value to an attribute. The attribute must
  70                be defined, the function can&#039;t create a new attribute.
  71                Defined both in gschem and libgeda, mainly because
  72                where different variables and information are available.
  73
  74
  75 Hooks
  76 -----
  77 Hooks are a way to define functions that will be called during different
  78 part of a programs execution. In gschem there are (currently) three
  79 different hooks available:
  80 * add-component-hook
  81 * copy-component-hook
  82 * move-component-hook
  83
  84 As their name indicate, they are called at different occasions. When
  85 you add a component add-component-hook is called, etc.
  86
  87 To add a function to be called you simply use the Guile funtion add-hook!.
  88 An example; to run the function auto-uref when you add a component you
  89 simply add the following line, preferrably in ${HOME}/.gEDA/gschemrc:
  90 (add-hook! add-component-hook auto-uref)
  91
  92 The function to be called from a hook (for example auto-uref above) has
  93 to accept one parameter, a list of attributes.
  94
  95 A small example that prints all attributes on a component to be placed:
  96
  97 (define (print-all-attributes attribute-list)
  98   (foreach (lambda (attribute) (display attribute)) attribute-list))
  99
 100
 101 How to use this
 102 ---------------
 103 The most complete example utilizing all of the above functions are in fact
 104 the auto-uref scheme script that currently is part of the gschem distribution.
 105 You can find it &lt;where gschem is installed&gt;/share/gEDA/scheme/auto-uref.scm.
 106 Uninstalled it&#039;s available at gschem/scheme/auto-uref.scm
 107
 108 All components have a reference designator that must be unique so
 109 gnetlist can handle it properly. By automatically assigning a number
 110 to each instance of a component when you place and copy it, you can
 111 simplify the naming operation.
 112
 113 All components has, per default, an uref attribute, for example uref=R?.
 114 The letter varies with component type. The auto-uref script enumerates
 115 uref based on what prefix the component has and assigns a number.
 116
 117 For example, the first component you place has per default uref=U? gets
 118 the attribute uref=U1. Next component with uref=U? gets uref=U2 and so on.
 119
 120 To be able to use the auto-uref script you simply add two lines in
 121 ${HOME}/.gEDA/gschemrc. They are:
 122 (load &quot;&lt;where gschem is installed&gt;/share/gEDA/scheme/auto-uref.scm&quot;)
 123 (add-hook! add-component-hook auto-uref)
 124
 125 If you want auto enumeration to work when you copy the component too, you
 126 simply add the following line:
 127 (add-hook! copy-component-hook auto-uref)
 128
 129 Good luck!
 130 </pre>
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