why input cannot be used in case??

[fahim1]

i want to use input in case but i have warning "Array type case expression must be of a locally static subtype."
how can i fix it?whats the soloution?
heres the code :

case mplr(1 downto 0)&'0' is
  when "000" =>  p1 := "00000000" ;

tnx

 

[barry]

Why are you bothering adding that '0'???? That's simply redundant.

case mplr(1 downto 0) is
      when "00"=>...

 

[TrickyDicky]

i want to use input in case but i have warning "Array type case expression must be of a locally static subtype."
how can i fix it?whats the soloution?
heres the code :

case mplr(1 downto 0)&'0' is
  when "000" =>  p1 := "00000000" ;

tnx

Because you're not allowed - its an annoying quirt of vhdl. You need to make an intermediate signal:

my_intermediate <= mplr(1 downto 0) & '0';
case my_intermediate is...

 

[barry]

Because you're not allowed - its an annoying quirt of vhdl. You need to make an intermediate signal:

my_intermediate <= mplr(1 downto 0) & '0';
case my_intermediate is...

That's still a waste of resources. (Which will probably be trimmed by the tool anyway).

 

[fahim1]

Why are you bothering adding that '0'???? That's simply redundant.

case mplr(1 downto 0) is
      when "00"=>...

its just part of code i have other parts
like
when "001"

 

[TrickyDicky]

its just part of code i have other parts
like
when "001"

if you did the code you describe:

case a(1 downto 0) & '0' is

when "001" =>

would be an impossible case - so it would be removed during compilation.

 

[std_match]

Because you're not allowed - its an annoying quirt of vhdl. You need to make an intermediate signal:

my_intermediate <= mplr(1 downto 0) & '0';
case my_intermediate is...

Is is better to use a variable as the intermediate value. It probably doesn't matter in a combinatorial process, but a signal will create a register and a delay in a clocked process.