Round-robin priority encoder

[Pasacco]

Dear

I am having problem to implement "circular round-robin" priority
encoder.

My goal is to implement using "generic" number of ports.

I tried to use two "for" loops.

Problem was that the index is not always increasing.

It seems that it is not possible to implement using generic.
If anyone has this experience, please let me know.

Manual implementation is below:
--------------------------------------------------------
-- 4-port circular round-robin
-- priority encoder
-- current : current pointer
-- req : request
-- next : next pointer
--------------------------------------------------------
process(current,req)
begin
case current is
when 0=>
if req(1)='1' then next<=1;
elsif req(2)='1' then next<=2;
elsif req(3)='1' then next<=3;
else next<=0;
end if;
when 1=>
if req(2)='1' then next<=2;
elsif req(3)='1' then next<=3;
elsif req(0)='1' then next<=0;
else next<=1;
end if;
when 2=>
elsif req(3)='1' then next<=3;
elsif req(0)='1' then next<=0;
elsif req(1)='1' then next<=1;
else next<=2;
end if;
when 3=>
if req(0)='1' then next<=0;
elsif req(1)='1' then next<=1;
elsif req(2)='1' then next<=2;
else next<=3;
end if;
end case;
end process;

 

[Pasacco]

It is not quite clear what normalized index means and how to use.

In this example of priority encoder,

input :
current: integer range 0 to 3;
req: array(0 to 3) of std_logic;

output:
nxt: integer range 0 to 3;

If you have some idea, please let me know -:

 

[Mike Treseler]

It is not quite clear what normalized index means

See Jonathan's variable declarations.
It means fix the vector dimensions
and direction to (A'length-1 downto 0).

If you have some idea, please let me know -:

I would consider using numeric_std.unsigned type
and the numeric_std.rotate_left function.
Related example:
http://mysite.verizon.net/miketreseler/sync_template.vhd
Good luck.

-- Mike Treseler