How dofor using generate or loop for this process ?

[Olivier Dir]

Hi all,
for this code I would like write this code with loop or generate.
I don't know if it's possible.



pSelFifo : process(Clk, SRst)
begin
if SRst = '1' then
SelFifo <= (others=>'0');
elsif Clk'event and Clk='1' then
if DataAvlble(1) = '1' then
SelFifo <= "000001"
elsif DataAvlble(2) = '1' then
SelFifo <= "000010"
elsif DataAvlble(3) = '1' then
SelFifo <= "000100"
elsif DataAvlble(4) = '1' then
SelFifo <= "001000"
elsif DataAvlble(5) = '1' then
SelFifo <= "010000"
elsif DataAvlble(6) = '1' then
SelFifo <= "100000"
else
SelFifo <= (others=>'0');
end if;

end if;
end process;

thank for your help.

Olive

 

[Brian Drummond]

On Tue, 01 Apr 2014 03:04:29 -0700, Olivier Dir wrote:

Hi all,
for this code I would like write this code with loop or generate.
I don't know if it's possible.



pSelFifo : process(Clk, SRst)
begin
if SRst = '1' then
SelFifo <= (others=>'0');
elsif Clk'event and Clk='1' then
if DataAvlble(1) = '1' then
SelFifo <= "000001"
elsif DataAvlble(2) = '1' then
SelFifo <= "000010"
....

thank for your help.

Olive

pSelFifo : process(Clk, SRst)
begin
if SRst = '1' then
SelFifo <= (others=>'0');
elsif rising_edge(Clk) then
SelFifo <= (others=>'0');
for i in DataAvlble'low to DataAvlble'high loop
if DataAvlble(i) = '1' then
SelFifo(i) <= '1';
exit; -- prevent multiple bit set, as in original
end if;
end loop;
end if;
end process;

 

[Olivier Dir]

Le mardi 1 avril 2014 13:25:02 UTC+2, Brian Drummond a écrit :

On Tue, 01 Apr 2014 03:04:29 -0700, Olivier Dir wrote:



Hi all,

for this code I would like write this code with loop or generate.

I don't know if it's possible.







pSelFifo : process(Clk, SRst)

begin

if SRst = '1' then

SelFifo <= (others=>'0');

elsif Clk'event and Clk='1' then

if DataAvlble(1) = '1' then

SelFifo <= "000001"

elsif DataAvlble(2) = '1' then

SelFifo <= "000010"

...



thank for your help.



Olive



pSelFifo : process(Clk, SRst)

begin

if SRst = '1' then

SelFifo <= (others=>'0');

elsif rising_edge(Clk) then

SelFifo <= (others=>'0');

for i in DataAvlble'low to DataAvlble'high loop

if DataAvlble(i) = '1' then

SelFifo(i) <= '1';

exit; -- prevent multiple bit set, as in original

end if;

end loop;

end if;

end process;

Thank you.

 

[Andy]

It is not clear from the example what is the index range on SelFifo, and if that range matches the range of DataAvlble. We do know that Selfifo has 6 bits. DataAvlble has at least 6 bits, indexed between 6 and 1 inclusive, but we do not know DataAvlble's index range direction.

The loop would only work if SelFifo'range is 6 downto 1.

The following would work if the index diretion of both DataAvlble and SelFifo is "downto", given the correct value for DaOffset:

pSelFifo : process(Clk, SRst)
constant DaOffset : integer := 1;
begin
if SRst = '1' then
SelFifo <= (others=>'0');
elsif rising_edge(Clk) then
SelFifo <= (others=>'0');
for i in SelFifo'reverse_range loop -- right to left in SelFifo
if DataAvlble(i + DaOffset) = '1' then
SelFifo(i) <= '1';
exit; -- prevent multiple bit set, as in original
end if;
end loop;
end if;
end process;

The sum (i + DaOffset) becomes a constant when synthesis unrolls the loop.

Andy

 

[Daniel Kho]

On Saturday, 5 April 2014 01:07:00 UTC+8, Andy wrote:

It is not clear from the example what is the index range on SelFifo, and if that range matches the range of DataAvlble. We do know that Selfifo has 6 bits. DataAvlble has at least 6 bits, indexed between 6 and 1 inclusive, but we do not know DataAvlble's index range direction.



The loop would only work if SelFifo'range is 6 downto 1.



The following would work if the index diretion of both DataAvlble and SelFifo is "downto", given the correct value for DaOffset:



pSelFifo : process(Clk, SRst)

constant DaOffset : integer := 1;

begin

if SRst = '1' then

SelFifo <= (others=>'0');

elsif rising_edge(Clk) then

SelFifo <= (others=>'0');

for i in SelFifo'reverse_range loop -- right to left in SelFifo

if DataAvlble(i + DaOffset) = '1' then

SelFifo(i) <= '1';

exit; -- prevent multiple bit set, as in original

end if;

end loop;

end if;

end process;



The sum (i + DaOffset) becomes a constant when synthesis unrolls the loop..



Andy

Something like this might just work (not tested):

signal n: positive;
....
pSelFifo : process(Clk, SRst) begin
if SRst = '1' then
SelFifo <= (others=>'0');
elsif Clk'event and Clk='1' then
if n>6 then SelFifo <= (others=>'0');
else
if DataAvlble then SelFifo <= to_unsigned(2**(n-1),6); end if;
end if;
end if;
end process;

Not sure though if this will synthesise. Probably not, since the expression (2**(n-1)) is not a constant. However, this can be replaced by a shift-left operation for synthesis. We could try that as well.

-daniel