Why is casez preferred than others?

I heard using 'casez' synthesizes into smaller hardware and casex could mask signals that are not initialized properly. Is this why casez is preferred over others?

x and z values as logic input only occur in simulation, never in hardware. Respectively the usage of casex and casez is a question of appropriate hardware simulation and if used in RTL code, of avoiding simulation mismatch.

FvM said:

x and z values as logic input only occur in simulation, never in hardware. Respectively the usage of casex and casez is a question of appropriate hardware simulation and if used in RTL code, of avoiding simulation mismatch.

Click to expand...

Why do we use casez over case? case statement seems to be the safest way to match the conditions exactly.

casez also provides a compact and descriptive way to specify don't care bits in RTL code.

FvM said:

casez also provides a compact and descriptive way to specify don't care bits in RTL code.

Click to expand...

My question is why would you want to use don't care over matching the conditions exactly, if this is just for simulation? Brute force matching (case) seems safer for validation.

stanford said:

My question is why would you want to use don't care over matching the conditions exactly, if this is just for simulation? Brute force matching (case) seems safer for validation.

Click to expand...

Because the Don't Care syntax is easier to read showing your intent rather than listing all the matching conditions, and less prone for mistakes. This is independent of simulation or synthesis

stanford said:

My question is why would you want to use don't care over matching the conditions exactly, if this is just for simulation? Brute force matching (case) seems safer for validation.

Click to expand...

One example of casez is to code a priority encoder (or servicing multiple interrupts based on priority). It makes easier to write the code, instead of writing multiple conditions using case statement.


casez ( intr [31:0])
32'b1zzzzzzz_zzzzzzzz_zzzzzzzz_zzzzzzzz : --------
32'b01zzzzzz_zzzzzzzz_zzzzzzzz_zzzzzzzz : --------
32'b001zzzzz_zzzzzzzz_zzzzzzzz_zzzzzzzz : --------
-------------
32'b00000000_00000000_00000000_00000001 : --------
--
endcase