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From: Kevin Neilson on 6 May 2008 19:15
I'd like to infer a DSP48 in XST and can't find a template that will
infer all of these opmodes:

P=M
P=M+C
P=P+M
P=P-M

(where M=A*B)

I can get XST to do any of these, one or two at a time, but when I try
to do all at once it adds a bunch of fabric. Any suggestions? The code
below, for example, properly connects up the ALUMODE pins (in a V5) for
the add/subtract function, but the mux that should be inferred as the
the DSP48's Z mux gets put in fabric instead, so P gets routed through a
fabric mux which feeds into C.
-Kevin

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.numeric_std.ALL;
entity xst_mac is
port (clk, reset, sel, add_sub: in std_logic;
A, B : in signed(17 downto 0);
C : in signed(47 downto 0);
P : out signed(47 downto 0));
end xst_mac;
architecture synth of xst_mac is
signal mult : signed(35 downto 0);
signal accum : signed(47 downto 0);
begin
process (clk)
begin
if (clk'event and clk='1') then
if (reset = '1') then
accum <= (others => '0');
mult <= (others => '0');
else
if (sel='0') then
accum <= C + mult;
elsif (add_sub='1') then
accum <= accum + mult;
else
accum <= accum - mult;
end if;
mult <= A * B;
end if;
end if;
end process;
P <= accum;
end synth;
From: Kevin Neilson on 7 May 2008 13:22
Kevin Neilson wrote:
> I'd like to infer a DSP48 in XST and can't find a template that will
> infer all of these opmodes:
>
....

Never mind--I don't think this type of inference is supported at the
time. -Kevin
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