[SOLVED] Which is more efficient way to write HDL code?

[amitjagtap]

hi all,
Which is more efficient way to write HDL code.
Bellow...which one is good...and why?
1st way----------
If Din=0 then ab<="00" else
If Din=1 then ab<="01" else
If Din=2 then ab<="10" else
If Din=3 then ab<="11" end if;

2nd Way------------
If Din=0 or Din=1 then a<=0 else
If Din=2 or Din=3 then a<=1 end if;
If Din=0 or Din=2 then b<=0 else
If Din=1 or Din=3 then b<=1 end if;

:lol:

 

[FvM]

Because both are equivalent, they will result in the same gate level logic. Readability would be my primary criterion, I guess the first is better in this regard. I would however use a case construct as third variant.

 

[amitjagtap]

Yes you are right....
Can you tell me the difference at synthesis level if i used 'if else' and 'Case' statement for the same logic.

 

[TrickyDicky]

it is going to depend on the code. They can produce the same logic, but if implies a preference where case does not.

 

[sv1437]

You can check that in the RTL schematic. The one with fewer number of gates is a better way.

 

[alexan_e]

Assuming that by

If Din=0 or Din=1 then a<=0 else
If Din=2 or Din=3 then a<=1 end if;
If Din=0 or Din=2 then b<=0 else
If Din=1 or Din=3 then b<=1 end if;

you mean

If Din=0 or Din=1 then ab(1)<='0'; else
If Din=2 or Din=3 then ab(1)<='1'; end if;
If Din=0 or Din=2 then ab(0)<='0'; else
If Din=1 or Din=3 then ab(0)<='1'; end if;

then these two should be the same but i would prefer the first way from your post.

Alex

 

[amitjagtap]

Ha.....
I haven't written the code for checking my syntax ....its for logic that i m asking..........

 

[imbichie]

You can synthesis both codes using the ISE and see which will take less LUT's and all. Less LUT means better coding