I'm trying to implement an add-compare-select (ACS) unit in a Spartan3 but I am not satisfied with the speed. The code looks like this:

... type sum_array is array(0 to 7) of signed(13 downto 0); signal state_reg : sum_array; ...

process(clk, rst) is

variable sum1, sum2, sum3, sum4 : sum_array;

begin if rst = '1' then .... elsif clk'event and clk = '1' then


sum1(0) := state_reg(a1) + gamma(a2); sum2(0) := state_reg(b1) + gamma(b2); sum3(0) := state_reg(c1) + gamma(c2); sum4(0) := state_reg(d1) + gamma(d2);


Reply to
Matthias Alles
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What's the current speed ? What would you like to achieve ?

Are the gamma constants ?

The only thing I see from a quick look is that you could "post-pone" part of the minimum mux.

For now, you have a MUX4 between the 4 sums. You could just assign state_reg_a to min2(sum1,sum2) and state_reg_b to min2(sum3,sum4). Then register the output of your other comparaison (to know whick of _a or _b is the good one), then do the mux the cycle after. And that mux can fit within the same LUT as the one that does the addition.

I have no idea if it will be really that much faster (or faster at all) because all you gain is a F5 mux and that gain could be couteracted by other factors ...

You can also take a faster speedgrade ;)


Reply to
Sylvain Munaut

sir i need vhdl code for viterbi decoder please snd me the code sir

Reply to

Sure no problem. Please make check out for £2350 + Vat.

Reply to
Andy Bartlett

One does wonder just what people think is on the other end of the conversation in a newsgroup.

Like Andy, I'm not going to work for free, but I'll happily help you out if you contact me off-group, with money in hand.

My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
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Reply to
Tim Wescott

It is certainly possible that one exists in, for example, opencores.

In that case, if one did reply, it would usually be with the link to the site and not the actual code.

Anyone remember the movie "Back to the Future" when the main character goes to a lunch counter and orders a "Pepsi Free" (which didn't yet exist)?

-- glen

Reply to
glen herrmannsfeldt

I should probably have pointed that out. "I need code, send it to me" just pushes a button with me, even though I know it's usually some student, possibly foreign, who is not being rude on purpose.

Sigh. I suppose I could give up being a curmudgeon for Lent, but then where would I be?

Tim Wescott 
Control system and signal processing consulting 
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Reply to
Tim Wescott

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