optimizing lookup table?

Status
Not open for further replies.
Y

Ye2x

Newbie level 4
Joined
May 2, 2012
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,328
hi,

i got a problem
can we group similar entry that give the same output in look up table

for example,
B <= "0000" when a = "0000" else
"0000" when a = "0001" else
"0000" when a = "0010" else
"0000" when a = "0011" else
"0001" when a = "0100" else
"0001" when a = "0101" else
"1111"

can we group the first four line into one command because the value of B will be the same for any input from 0 to 3?

thanks
 

The question hasn't to do with optimization, which is performed by the synthesis tool anyway. It's just a matter of typing effort.

You can combine the first four compares to
Code: 
"0000" when a(3 downto 2) = "00"
similarly combine the next two lines.
 

i see, so we can combine till the last bit that will be same?

for example,
B <= "00000000" when a = 1 until 18
B <= "00000000" when b = 19 until 24

can we do the same like before?
 

assuming a is a signed or unsigned type, you could use comparitors:

Code: 
C <= "0000" when a >= 1 and a <= 18 else
  <= "0001" when b >= 19 and b <= 24 else
...
--etc

Remember, with 2 on the right hand side, this will build a priority encoder.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…