mirror of
https://github.com/xodio/xod.git
synced 2026-03-04 07:54:04 +01:00
109 lines
4.0 KiB
Markdown
109 lines
4.0 KiB
Markdown
---
|
||
title: Program Structure
|
||
---
|
||
|
||
Program Structure
|
||
=================
|
||
|
||
XOD programs are quite similar to electronic circuits. To build an
|
||
electronic circuit, you use various electronic components and connect them
|
||
with wires. In a XOD program, you use *nodes* and connect them with *links*.
|
||
|
||
|
||
|
||
Nodes
|
||
-----
|
||
|
||
What a node does depends on its type. Just as there are ICs in the physical
|
||
world to control motors, amplify audio signals, and store data, in XOD there
|
||
are many types of nodes available. You can also easily create your own.
|
||
|
||
Some nodes represent physical devices like LEDs or digital thermometers. Others
|
||
are used to transform and filter data. Here are few examples:
|
||
|
||
* [`thermometer-tmp36`](/libs/xod/common-hardware/thermometer-tmp36/)
|
||
* [`console-log`](/libs/xod/core/console-log/)
|
||
* [`add`](/libs/xod/core/add/)
|
||
* [`to-percent`](/libs/xod/core/to-percent/)
|
||
|
||
You place the nodes you’ve chosen for your program into slots to be later
|
||
connected with links.
|
||
|
||
Pins, inputs, and outputs
|
||
-------------------------
|
||
|
||
Nodes alone are black boxes. They expose *pins* to support interaction. Think
|
||
of pins as of sockets, ports, IC legs, and jacks.
|
||
|
||
A pin can be either an *input* or an *output*. Once you feed a new value to an
|
||
input, the node is evaluated. In response, it may update the values on its
|
||
output pins or interact with the real world in some way, e.g. change a motor's
|
||
speed.
|
||
|
||
Some nodes send an output on their own as a reaction to some external event.
|
||
For example, the [clock](/libs/xod/core/clock/) node sends outputs at regular
|
||
time intervals.
|
||
|
||
Pins are depicted as holes with short labels. Inputs are placed at the top
|
||
of the node, and outputs are at the bottom.
|
||
|
||
|
||
|
||
Links and values
|
||
----------------
|
||
|
||
Nodes talk to each other by transmitting values over *links*. A link is a kind
|
||
of wire that you use to connect one node's output to another node's input.
|
||
|
||
Values in XOD are quite similar to electric signals. However unlike their
|
||
electric counterparts, they can carry not only raw voltage values, but also
|
||
more sensible data like arbitrary numbers and text strings. Learn more about
|
||
values in the [Data Types](../data-types/) article.
|
||
|
||
In analog electronic circuits voltage levels change continuously and
|
||
simultaneously at all points. There is no such thing as “this chip would think
|
||
first, than another chip would think”. In digital electronics however many
|
||
updates are accompanied with discrete pulses which are sourced by a
|
||
microcontroller and called clock signals.
|
||
|
||
Values behave very similarly in XOD. They change and propogate instantly. These
|
||
cascading value updates are called *transactions*. In XOD, the role of clock
|
||
signals is played by *pulses*. The [Execution Model](../execution-model/)
|
||
article describes how they work in detail.
|
||
|
||
There are a few rules that define which pins are allowed to be linked and which
|
||
are not. They are intuitive enough, but for a formal description see [Linking
|
||
Rules](../linking-rules/).
|
||
|
||
Patches
|
||
-------
|
||
|
||
Nodes linked together form a *patch*. Patches are like modules, documents, or
|
||
files in other programming systems.
|
||
|
||
You would have a single patch in a simple project, while you’d likely have
|
||
many for complex projects.
|
||
|
||
What makes a patch interesting is that once you’ve created one you can use it
|
||
as a new type of node in other patches! That’s the main idea behind XOD
|
||
extensibility.
|
||
|
||
You use special *terminal nodes* to denote input and output pins when a patch
|
||
is used as a node.
|
||
|
||
<div class="ui segment">
|
||
<span class="ui bottom attached label">
|
||
Photo by
|
||
<a href="https://www.flickr.com/photos/26735065@N00/">cutwithflourish</a>.
|
||
</span>
|
||
<p>
|
||
<span class="ui blue ribbon label">Note</span>
|
||
Perhaps you’ve heard of modular synthesizers - they are very similar to XOD
|
||
programs. Nodes are modules, links are CV cables with banana connectors,
|
||
and patches are a rack chassis for modules.
|
||
</p>
|
||
<div class="ui fluid image">
|
||
<img src="modular-synth.jpg" alt="Modular synth" />
|
||
</div>
|
||
</div>
|