kicad-developers team mailing list archive

[Dan Weatherill <dan.weatherill@xxxxxxxxxx>]

    Hi all,
    I've been using kicad for about 5 years. Recently (mostly with CERN 
changes - especially differential pair support), it's become suitable 
for more and more of my more complex projects (I'm switching from Altium 
Designer). I also have about 10 years experience working on c++ 
projects, but am not what you would call an "expert".
    A feature I've been especially missing in Kicad for several 
projects is something akin to Altium's "harnesses": that is, basically a 
"bus-like" entity which contains named signals, possibly of different 
types (e.g. input, output, passive etc). Harnesses are very useful for 
drawing things like e.g. SPI, I2C, CAN connections which have well 
defined named signals. Harnesses contain better information than 
numbered busses for this application, but can help with schematic 
"overcrowd" when wiring up chips with many signals such as micros, FPGAs 
etc. This is often a big problem especially in hierarchical designs 
where to do this using wires requires possibly dozens of hierarchical 
labels.
I've been thinking about implementing this for a while, but have not 
started due to being aware that eeschema is under fairly major 
re-factoring at present.

    With guidance from c4758p on #kicad, I think that this feature 
could be implemented with the following steps:
1) add two new items in NETLIST_ITEM_T enum, likely called NET_HARNESS 
and NET_HARNESSLABELMEMBER, which have similar functionality to NET_BUS 
and NET_BUSLABELMEMBER but for harnesses
2) several changes to connection rules in netlist.cpp (most majorly in 
pointToPointConnect() and a new function 
NETLIST_OBJECT_LIST::connectHarnessLabels() )

3) minor UI additions (harnesses can be just a different colour wire, 
and harness-to-wire connections at this time can be just the same as 
wire-to-Bus connections)

The main question usability wise would be how to label harnesses. I see 
two possible options:
1) new syntax: a harness has a label using new type of brackets, with 
harness type in brackets, e.g. an I2C bus called A would be "A{I2C}". 
The wires would be then labelled exactly like bus labels, e.g.: "A[SCL], 
A[SDA]"

2) bus-like syntax: using same brackets as bus syntax, but make a 
harness when the contained type is a string rather than numbers, i.e. 
"A[I2C]" for harness label, "A[SCL], A[SDA]" for harness members.


I guess there are implications for the schematic file system which I 
need to understand, and need to be discussed.

All suggestions welcome, and I hope to start working on this soon.
Thanks,
Dan W