kicad-developers team mailing list archive

[Chris Pavlina <pavlina.chris@xxxxxxxxx>]

On Thu, Sep 15, 2016 at 04:06:13PM -0400, Wayne Stambaugh wrote:
> On 9/15/2016 1:54 PM, Dan Weatherill wrote:
> >     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]"
> 
> You have to be careful here.  Using curly brackets in labels hasn't been
> defined in the schematic editor so users may have used them for some
> personal notation.  I think the risk is low but breaking someone's
> schematic is no going to make them happy.

IMO, if this is implemented properly, the labels shouldn't have an
effect unless they connect to a harness anyway, so existing schematics
shouldn't be affected.

> 
> > 
> > 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.
> 
> Whatever support you are going to need to implement this in the
> schematic file format needs to be discussed soon because I'm hoping to
> start on that in the not too distant future.
> 
> Also be aware that there are going to be some major refactoring of the
> eeschema core code so if you start before that gets completed, be
> prepared for lots of disruptions to your work.
> 
> > 
> > All suggestions welcome, and I hope to start working on this soon.
> 
> Since this is a major change to the schematic editor, it would also be
> useful if you write up a detailed blueprint on how you are planning on
> implementing harnesses so other developers can comment.
> 
> > Thanks,
> > Dan W
> > 
> > 
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