This file contains notes on library Portable.  It is kept by date, most recent
entries first.  Use the GRIPE command to ask questions or comment on library
VDEG_Portable.


21-Aug-1989	Paul Menchini
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I've added a clock port to the JKFF component in VDEG_Portable.Components, as
it (erroneously) did not have one.  The port is called "Clk" and appears immed-
iately prior to the "Clr" port.


27-Jul-1989	Paul Menchini
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Per the decision at the VDEG meeting earlier this week, I've changed the type
of all input ports of the components in package VDEG_Portable.Components to
scalars, except for those components that are generic in their number of
inputs.  I've also improved the formatting by adding explicit modes to all
generics and using tabs to align the generic and port lists of all components.


07-Jun-1989	Paul Menchini
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I've done some further review and made several small changes.  In the package
body for the Types package, I've changed statements of the form "if <condition>
then exit; end if;" to "exit when <condition>;".  In the Components package,
I've fixed mode errors on the flip flops, and changed all generics of type
Delay to be of type Time.  Since package Timing gives ways of supplying min-
nom-max information, the type Delay us unnecessary.


12-May-1989	Paul Menchini
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Library Portable consists of the files TYPES.VHDL, TYPES-BODY.VHDL,
COMPONENTS.VHDL, and TIMING.VHDL.  These files are as agreed to by the
attendees of the 9-10 May VDEG meeting, with the following exceptions:

    1.	The package Vector_Comp_Ops and its corresponding body are not included
	in library Portable.  After rethinking over the whole issue of
	comparison operators, I now agree with the position of those who wish
	to include the comparison operators "<", "<=", ">", and ">=" in
	numbering-system-specific packages and not in the basic types package.
	I am keeping the definitions of these operations around in case we
	change our minds, but have not included them in any of the posted
	packages.

    2.	In keeping with the above change, I've deleted the same operators
	returning Logic4 from package Types and its corresponding body.

    3.	The first line of all operators on Logic4 arguments now assert that
	neither of their inputs are equal to 'Z'.  During the VDEG meeting, it
	was asserted that these functions do an implicit Sense, but the
	implicit second parameter is always 'X'; I feel it's much better, when
	using these functions, to do an explicit Sense, hence the prohibition
	on 'Z'.  Note that, since the Vector4 operations use the Logic4
	operations, they also disallow 'Z'.

    4.	One of the suggestions made during the VASG is that the "=" and "/="
	operations having Logic4 arguments and returning a Logic4 result be
	defined in terms of xor.  We decided that this wasn't necessarily a
	good thing to do, but I did decide to define "/=" in terms of "="; I
	also defined "nand" in terms of "and", and "nor" in terms of "or" while
	I was at it.

    5.	The Sense functions working on vectors now use an alias to normalize
	the input vector rather than maintaining two indices (one for the
	input, one for the result vector).

    6.	I changed the name of the "DataOut" port of the ROM component in
	package Components.  It now has the name "Data".