kicad-developers team mailing list archive

[Chris Pavlina <pavlina.chris@xxxxxxxxx>]

On Thu, Sep 15, 2016 at 06:54:59PM +0100, 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 _really_ want this. IIRC I submitted a wishlist item for it ages ago,
and nothing ever really became of it (and as usual I ran out of time to
implement it myself). These are hugely useful in complicated designs.

> 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:

For anyone who doesn't know yet, I'm c4757p on #kicad, or c4758p when my
connection's dodgy ;)

> 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)

In light of the proposal to add line color support to eeschema, I'd like
to see something different than just a color. They look like this in
Altium:

http://techdocs.altium.com/sites/default/files/wiki_attachments/231555/Harness+Connector+with+entries.png

A point wrt. UI is that when eeschema is converted to GAL, a good bit of
the UI code will need to be ported or thrown out. I don't think that
should necessarily stall development, but I'd warn you to be prepared
and write your code to be properly modular and easy to port. :)

> 
> 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 haven't given this a huge amount of thought yet. Does anybody see a
reason for this to me more than just a stylistic detail? We discussed
this a bit on IRC and concluded that it would matter if harnesses were a
subclass of buses, but if they're a separate object I don't think so.

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

As far as I can see, we just need to add a 'harness' type similar to the
'bus' type.

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