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Buses

When you have a complex patch, drawing all links as visible straight lines may produce much of visual noise.

Many link intersections

Buses are an alternative way to link nodes’ pins. They allow creating “invisible” links. There are two node types in xod/patch-nodes that work in tandem:

to-bus — defines a new bus
from-bus — sources data from an existing bus

Bus nodes with the same label are considered to be implicitly interconnected by XOD.

Note

Buses are used in electronics extensively. You’ll rarely see many wires on schematics leading toward a single GND (Ground) point or Vcc (power source). Instead, the wires are terminated with special symbols of GND and Vcc buses, and anyone understands that all the symbols are effectively connected together.

XOD borrows the idea from electronic schemes.

We can refactor the patch shown above using buses to reduce the visual clutter:

Refactoring with buses

The triangles are bus nodes. The one pointing down is a to-bus sink, and the up-triangle is from-bus source. Pay attention, how we used two terms I2C and ADDR to label the bus nodes. In other words, we’ve introduced two buses to our patch.

The bus nodes do not affect performance or other characteristics of the compiled program anyhow. When XOD transpiles a program, it replaces all matching bus node pairs with a straight link.

Buses are local to the patch where they are defined. That is, two different patches may have a bus with the same label, and they will not be related anyhow. There is no way to teleport a link from one patch to another, use the patch nodes mechanism to achieve it.

IDE shortcuts #

It might be annoying to place a to-bus and from-bus, then giving both a label manually for each bus link. XOD IDE provides a few keyboard shortcuts to assist you when dealing with buses.

You can start linking and when you see the rubber link which follows the cursor press the B key. It will create a bus node under the cursor with a label matching the pin name which started the link.
You can select an existing link or several links at once and press the B key to convert the selected links into buses: the links are broken, and a matching bus pair labeled after output pin is created.

When to use buses #

Line intersections—especially with small angles—make patch reading hard. When a link introduces many intersections, replace it with a bus.

When you feedback an output back to an input of some upstream node, the reverse link might seem awkward. Replacing it with a bus is a good idea.

Delivering a common constant or an input like RST, UPD, or ADDR to multiple places may introduce bulky webs. Replacing them with a bus will make a patch much lighter.

On the other hand excessive use if buses might make a patch harder to follow visually. So, if you’ve made three or more buses on a patch, ask yourself whether it will be better to extract some parts of it into separate patches.

Validity rules #

To be successfully compiled the bus nodes should follow several pretty intuitive rules:

A from-bus node should have a corresponding to-bus node with the same label. Otherwise, it will mean a floating undefined value.
There should be no more than a single to-bus node with a particular label on a patch. Otherwise, it would be possible to link an input to multiple outputs which make no sense in XOD.
The data type of an input linked to from-bus should be castable from a type of the matching to-bus node.

If a bus violates some rules, it will be rendered red in XOD IDE. Hover the node to see the error details.