Re: [phdl-devel] Device Attributes

[Peter D. <hd...@ho...>]

I vote for FOOTPRINT for the physical layout shape to be associated with the part.

Other terms I have seen are PKG_TYPE (Mentor DxDesigner) and DECAL. 

-----Original Message-----
From: Wesley J. Landaker [mailto:wj...@ic...] 
Sent: Sunday, January 26, 2014 1:56 PM
To: phd...@li...
Cc: Peter Dudley
Subject: Device Attributes

In my message about PHDLIF, I asked about attributes:

On Friday, January 24, 2014 22:42:56 Wesley J. Landaker wrote:
> 4. Speaking of attributes ... what attributes do certain backends expect?

Here are some of my thoughts about attributes for devices that I'd love to get feedback on:

1. The structural two parts of devices we capture in PHDLIF are the device name and its list of pins. The rest is attributes. Let's look at the structure for second:

	* Name -- this is the low-level name of the device. This is not intended to be the friendly "user" name the PHDL user might have given their part {"FPGA", "ADC"} but instead is the "real" name of the device {"XC6LX45-1-CSG324I", "MAX1112EEE+"} that should match the datasheet. (For reference, In PHDL 2.x this was the "PARTNUMBER" attribute, but in 3.x it is part of the device structure.)

	* Pins -- the pins on the device. Again, this is not the friendly "user" pin names the PHDL user might have given {"clock", "data[5]"}, but are the "real" names of the pins from the device declaration {"AA17", "12"} that should match the datasheet.

In a sane world, this might be all we'd need, since this is how real designers refer to parts on their boards {"clock is hooked to pin AA17 of the FPGA"}. But pragmatically, we need more than structural information to work with most PCB tools.

2. Here are the "standard" device attributes I think we need. (Not worried too much about names yet, until we know semantically what are we trying to
communicate.)

	* Part number -- this here to show that I'm not forgetting this, but this is actually just the device name, as described above. This is always guaranteed to be present, so there are no edge conditions here.

	* Package / footprint -- usually a designer picks a part atomically, package and all, but some PCB tools like to separate the part number and the package or footprint type. This is like PHDL 1.x's "PACKAGE" attribute and PHDL 2.x "FOOTPRINT" attribute[1]. Since it seems that about 50% of backend formats require this information split out, whether or not the *user* wants it split out, my thought is that there are two ways to handle this: A. Leave the attribute optional (since many tools don't need or want this
information) and leave the backend to do something quasi-intelligent if its not provided (like reuse the part number for the footprint name), or B. make package/footprint information part of the first-class structure of PHDL devices (thus making it required for the user to always provide). I'm a little torn here. Any thoughts?

	* Library / collection -- I'm not sure why -- since part numbers are already unique in a global namespace -- but every PCB tool seems to insist that all parts be part of a name library or collection. This is like PHDL 2.x's LIBRARY attribute. This is fine, and kind of nice from an organizational point of view *when the user wants it*, but it is a little obnoxious that it is *required* by some tools, especially where there is no global library/collection hierarchy to follow. My thought here is that if this attribute is not provided by the user, and there is no way to indicate "no library" in a particular backend, netlisters should default to a default (but documented) library name {"default" if there is nothing better, "work" 
for VHDL, and so forth}.

Obviously there are a zillion other attributes that CAN go on devices, that might be useful for certain backends. For example, BOM generators need to know about values for parameterized parts {resistors}, and can use extra info like manufacturer, supplier, price, etc for making reports. We should standardize on names for those as well, but first I want to make sure we're on the right track for fundamental attributes needed during primary netlisting.

Footnotes:
[1] Okay, I said I didn't care about names yet, but seriously, what is the standard PCB terminology here? Package, footprint, or something else?! For reference, we changed from PACKAGE to FOOTPRINT only because "package" was a keyword in PHDL 2.x, not for any other super insightful reason.