Conversion for different packages

[Binome]

Hi,
I'm using : R<= unsigned(ext(A, N)) + unsigned(ext(B,N));
with ieee.std_logic_arith library.A, B, and R are std_logic_vector.
Now I know it's not a recommended library I want to use numeric_std. ext() is not known so I have to use another function. I'm trying to use to_unsigned like that:
R<= std_logic_vector(to_unsigned(unsigned(A), N) + to_unsigned(unsigned(B),N));
But Modelsim can't compile, the error is "No feasible entries for subprogram "TO_UNSIGNED"."
Can someone tell me why?

 

[lucbra]

I assume you have declared to use the library numeric_std?

use ieee.numeric_std.all;

 

[TrickyDicky]

converting A and B to unsigned is fine, but there is no to_unsigned function for an unsigned type, thats only for integers. You're after the resize function:

R < std_logic_vector(resize(unsigned(A), N) + resize(unsigned(B), N));

 

[Binome]

Thanks, it's ok.