He
isn’t trying to modify the signedness of T, or create a new
type that is like T but with a different signedness. He is
trying to construct a packed array with elements of type T,
and set the signedness of that new packed array type.
This
is related to another deficiency in the language. When you
compose packed arrays of packed arrays, there is no way to
independently control the signedness of each level. The
language only allows you to set the array to signed at one
level. You can declare an unsigned word that is an array of
4 signed bytes, or a signed word that is an array of
unsigned bytes. But there is no way to declare a signed
word that is an array of signed bytes.
For
the 2005 standard, Cadence proposed a syntax for declaring
packed arrays that would allow separately specifying the
signedness at each dimension. But nobody else seemed to
understand what that meant, until after something had been
standardized that was incompatible with it and it was too
late. It should still be possible to support it in a
backward compatible way using typedefs for each level that
needs to be signed, but it requires allowing the syntax
Radoslaw is trying to use here, i.e.
typedef
logic signed [7:0] mybyte;
typedef
mybyte signed [3:0] myword; //signed word composed of signed
bytes
And
type T is implicitly unsigned. There are no rules to explain
how you could override the signedness of a type.
I
don't see that the BNF allows it.
type_identifier
can be followed by packed_dimension, but I don’t see that it
can be followed by 'signing'.
Shalom
typedef
reg T;
T signed [1:0] r;
Is
it legal ?
I cannot find reason why nobody supports it
Regards,
Radek
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