Re: gEDA-user: Heavy Symbols and such

[Dave N6NZ <n6nz@xxxxxxxx>]

Steve Meier wrote:
> Dave,
> 
>
> 
> I have been thinking that the way to do back annotation is to add a
> schematic level attribute that is attached to a symbol. Something like
> 
> C 8500 9600 1 180 0 big_fpga-1.sym
> {
> T 8300 9100 5 10 1 1 180 0 1
> refdes=U1
> T -100 -100 5 10 1 1 180 0 1
> pinswap=a12,g13
> }
> 
> This could then be used when viewing the schematic or generating a
> netlist to swap the two pins.

This seems like a good idea.  In fact, it strikes me as very similar to 
the "slots" concept.  With slots, we have "numslots", "slot", and 
"slotdef".  Perhaps pin swapping has an orthogonal set of attributes. 
Of course, pin swapping interacts with slot swapping -- think of our old 
friend the 74xx00 -- four slots, each with swappable inputs within the slot.

I suppose today one could define 8 slots for a 7400, sounds a little 
odd, but the point is you would only use 4 of them at a time.  Each slot 
would be defined twice -- once for each possible swap. Obviously, this 
leads to combinatorial explosion, but for practical parts it might be 
OK.  I think the right answer is that slots map pinseq #'s onto logical 
pins, and "swaps" map the logical pins onto physical pins, which 
requires an extra layer of symbolic pin names in between slots and swaps 
that does not currently exist.

I like the idea of the netlister being able to read a file of slot=N and 
swap=N attributes and generate the netlist accordingly.  Then after the 
layout is done, gschem could import the same file to update the 
attributes to accomplish back-annotation.

And let's not forget my desire to target multiple package pin-outs -- 
but I think that can be handled by creative use of slots, although its a 
bit of a hack.

-dave
> 
> Steve Meier
> 
> On Wed, 2007-12-05 at 10:13 -0800, Dave N6NZ wrote:
>> Steve Meier wrote:
>>> Eventually, I would also like to see being able to define the logic
>>> level for a group of pins, can the pins be used differentialy? if so
>>> which pins are paired? Can we swap pins if so which ones? 
>> The pin swapping question brings up another of my pet peeves -- when the 
>> same part comes in packages with different pin outs, it needs different 
>> symbols.  Although -- last night it occurred to me that I could use 
>> slots to fake that out.  Even if the part isn't slotted, I could define 
>> a slot for each package pin out.
>>
>> But it really points out the fact that there is a level of abstraction 
>> missing in the current symbol definition, and that interacts with back 
>> annotation from what ever PCB layout tool you are using.  Maybe the 
>> netlister needs to be enhanced to be a more interactive tool instead of 
>> a one-way translator to make all the work well.
>>
>> -dave
>>


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