Subject: Re: Enumerated Types Proposals
From: Clifford E. Cummings (cliffc@sunburst-design.com)
Date: Mon Apr 08 2002 - 12:39:13 PDT
Peter -
I really like the enum [data_type] proposal but would like to suggest one
small change. I don't want to be required to make the explicit logic
declaration when the context is clearly 4-state.
Proposed wording?
In the absence of a data type declaration and if no values are assigned,
the default data type shall be int. If only binary values are assigned to
the enum names, the default data type shall be int, If no data type is
assigned and the enumerated names have assigned values that include x's and
z's, the default data type shall be logic. This means that an enumeration
that defaults to a data type of int because the enum names were either
unassigned or were originally assigned binary values will default to a data
type of logic, after the design is recompiled, if x-assignments or
z-assignments are added to the enumeration when the design file is
modified. Any other data type requires an explicit data type declaration.
We still need to comment on what should happen if an unassigned enum name
follows an enum name with x or z assignments. Is this a syntax error or do
names S1 and S2 take on consistent defined values?
// IDLE=2'b00, XX=2'bx, S1=??, S2=??
enum {IDLE, XX='x, S1, S2} state, next;
Otherwise, I really do like this proposal.
Regards - Cliff
At 12:05 PM 4/8/02 +0100, you wrote:
>Kevin,
>
>If a value is not specified, then the following from Cliff should apply:
>
>Draft 4, Section 3.6 - page 8
>Section 3.6 - Paragraph #2 Clarification Proposal
>PROPOSAL: modify the second paragraph as follows:
>The named values can be cast to integer types, and increment from an
>initial value of 0. This can be over-ridden. If integers are assigned to
>some but not all of the named values, unassigned named values are
>implicitly assigned an increment of the previous explicitly or implicitly
>assigned integer.
>enum {bronze=3, silver, gold} medal; // silver=4, gold=5
>enum (a=3, b=7, c) alphabet; // c=8
>
>Peter.
>
>At 10:30 AM 4/5/02 -0800, Kevin Cameron wrote:
>>
>>
>>Peter Flake wrote:
>>> Cliff,
>>>
>>>We have considered your proposals, and we have a counter-proposal which
>>>we think should satisfy your requirements.
>>>
>>>We propose an optional data type with the enum. The default data type
>>>is int
>>>
>>>enum [data_type] { enum_member {, enum_member} }
>>>
>>>The data type is limited to integer data types, 2 state or 4 state. The
>>>4 state data types can have constant values containing X or Z.
>>>For example:
>>>enum logic [1:0] { S0=2'b00, S1=2'b01, S2=2'b11, XX='x } state, next;
>>>
>>>Peter.
>>What values get assigned if a value (or part of it) is not specified?
>>
>>Maybe want a default:
>>
>> enum [data_type] [ = <default value>] { enum_member {, enum_member} }
>>
>> e.g.:
>> enum logic [1:0] = 2'b00 { S0=1'b0, S1=1'b1, S2=2'b11, XX=2'bxx }
>> state, next;
>>
>> which extends as:
>> enum logic [2:0] = 3'b100 { S0=1'b0, S1=1'b1, S2=2'b11, XX=2'bxx,
>> BAD } state, next;
>>
>>// BAD takes default ==3'b100
>>
>>Note: since enums in C always allocate specific numbers (regardless of
>>the compiler)
>>mixing code from different compilers does not cause a problem (wrt
>>enums). The
>>same should (IMO) be true for SystemVerilog enums.
>>
>>Kev.
>>
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