Editing Busports

= Introducing Busports =

* Notionally, busports act as ganged sources or sinks.
* A connection between busports represents connection(s) between the underlying ports.<br />
[[File:prots.png|prots.png]]<br />
[[File:No_ports.png|No_ports.png]]

= Any Block Can Be Bussified =

* Right click on a block to toggle source/sink bus feature.
* Toggling will scrub connections on the bus.<br />
[[File:toggle.png|toggle.png]]

= A Key to Reading Busports =

* Busports are wildcard colored (white).
* They're fatter than ordinary ports.
* To the left of the hash is the index of the port.
* To the right is the number of ports represented by the busport.<br />
[[File:close-up.png|close-up.png]]

= Busport DTD Issues =

* <!ELEMENT block (key, param*, bus_sink?, bus_source?)> 
** For GRC flowgraph files.
** The xml definition for a block may now contain bus_sink or bus_source fields.
** These fields follow the params fields, sink first followed by source.
** Busports are binary... if the field exists, they're on.
* <!ELEMENT block (name, key, category?, throttle?, import*, var_make?, make, callback*, param*, bus_sink?, bus_source?, check*, sink*, source*, bus_structure_sink?, bus_structure_source?, ** doc?,  grc_source?)>
** Likewise for block XML definitions.
** bus_structure_sink and bus_structure_source are optional fields following the sink and source fields.

= Wait a Second... bus_structure? =

* Yep, there's actually a reason for including the bus index in the port label: there can be multiple busports per source/sink, and they're pretty flexible.
* [ [i_{0,0}, i_{0,1}, … , i_{0,m_0}],<br />
[i_{1,0}, i_{1,1}, … , i_{1,m_1}],<br />
…<br />
[i_{n,0}, i_{n,0}, … , i_{n,m_n}] ]
* Python list of lists naming the indices represented by each port.<br />
[[File:multi-busses.png|multi-busses.png]]

= What Does It Mean to Connect? =

* When you connect the j^th source busport to the l^th sink busport, source port i_{j,k} is connected to sink port i_{l,k} for each k in {0, 1, … , m_j}. It's up to the user to ensure sink and source ports correspond in type and number.
* What if you don't specify the bus_structure to define these indices? One will be provided for you.<br />
Here's the default:
<pre>[ [0,1,...,m] ]</pre>
(m is the total number of ports).<br />
[[File:bus_connections.png|bus_connections.png]]

= Busports and Hier Blocks =

* First, pad sources and sinks support multiple streams (nports). You can bussify pads (or any other block with sources/sinks).
* There are new Bus Source/Sink and Bus Source/Sink Structure properties for defining hier block XML files.
* You can use variables or parameters in bus_structure_sink/source properties (just as you can with nports).<br />
[[File:heir_block.png|heir_block.png]]

= Some Details (FWIW) =

* When a source/sink is bussified, GRC adds a port of type “bus” for each index list in the source/sink structure (by default, there is one).
* GRC keeps its port lists sorted, so busports come at the end of the list. Keys for busports will show up in the connections list of a .grc file.
* Busports are a GRC-centric concept. Busports affect the python generated by GRC in that they shape connections lists, but busports themselves don't show up in the python.

= Motivation =

* BER curves need lots of connections!(github/namccart/fecapi)
* In general, GRC should evolve to do more dynamic/inductive things. The nports property represents a first small step in that direction, but what good is it to create an arbitrary, variable-dependent number of ports if you still have to connect all the ports manually?
* I expect there to follow more improvements to GRC yielding a visual language for “doing things n times” and generating corresponding python. 
* What Python(ic) features are worth encoding visually as stream-processing features?