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Re: where footprints come from (was Re: Re: Internal


Werner Almesberger wrote:
Dick Hollenbeck wrote:

(units mil)
(resolution 10)
(const variable_def 30.4)

Do you really need the resolution if you already have floating-point
and a free choice of units ?

Probably not. It needs further thought. I duplicated something from specctra, and like all of this, the implementer would have to go back and justify each adoption by spending more time thinking about it.

We really don't need much in terms of expression support. Simple mx+b support is about all for positioning a pad with given shape.

Yes, you usually don't need higher math. If you want to stay close to
the respective reference material (i.e., use the same parameters as a
basis), you may need to add or subtract distances and quite often
divide them by two. Multiplications come in the form of
dimension*integer or dimension*(integer+/-0.5).

Things get a little more interesting if you want to create more than
one footprint from a single definition, e.g., DIL/SIOC/SSOP/QFN/etc.
families. Also, large BGAs are basically begging for some nestable
loop construct.

I don't want to do that. Copy the part, add the pins. This can be done in a text editor with the enhanced copy and paste I suggested. The format must be simple and loops I think overstep this goal. By simple, I mean the footprint editor has to be able to edit the file in a WYSIWIG mode, i.e. graphical editing mode as now. I would not commit to coding the looping support. How do you name pins in a loop without introducing a reasonably rich programming language? Then such language is not easily editable in a WYSIWYG mode. We cannot make commitments for anyone else. So writing a specification without a commitment to code it is pointless. I am trying to suggest things I suspect somebody can code in short order.

Here is another important point:

The simpler the footprint file is, the more easy it is to use a text editor on it. In the end, a text editor is a tool that everyone is familiar with. Copying lines of text is easy.

In fact, I might even dumb down

(expr 0 + variable_def * 1)


(mx+b variable_def 1 0)

where "mx+b" would be a keyword, or maybe muladd.

What's your opinion on measurements ? E.g., like here:

I think you mean "dimensions"? I like them, in particular when these footprints need to be printed to PDF or hardcopy. However, these measurements can be obtained in the footprint editor using the space bar to set a local origin. The cost benefit ratio of dimensions are too high for me personally to ever consider implementing them for free.

But I think they were drawn manually, so there's no automatic
correlation of the numbers displayed and the real distance.

For comparison, all the measurements shown here are automatic (and
adding a measurement is a matter of seconds):

How is this done? What software?


Yup, as simple as possible but not simpler :)



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