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Replaced recursive lcu scheme with bk adder

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Clifford Wolf 2014-08-18 00:03:33 +02:00
parent acb435b6cf
commit 4b3834e0cc
1 changed files with 30 additions and 60 deletions
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88
techlibs/common/techmap.v
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@ -285,80 +285,50 @@ module \$__alu_ripple (A, B, CI, X, Y, CO, CS);
endgenerate endgenerate
endmodule endmodule
module \$__lcu_simple (P, G, CI, CO, PG, GG); module \$__lcu (P, G, CI, CO);
parameter WIDTH = 1; parameter WIDTH = 2;
input [WIDTH-1:0] P, G; input [WIDTH-1:0] P, G;
input CI; input CI;
output reg [WIDTH:0] CO; output reg [WIDTH:0] CO;
output reg PG, GG;
wire [1023:0] _TECHMAP_DO_ = "proc;;"; integer i, j, k;
reg [WIDTH-1:0] p, g;
integer i, j; wire [1023:0] _TECHMAP_DO_ = "proc; opt -fast";
reg [WIDTH-1:0] tmp;
always @* begin always @* begin
PG = &P; p = P;
GG = 0; g = G;
for (i = 0; i < WIDTH; i = i+1) begin
tmp = ~0; // in almost all cases CI will be constant zero
tmp[i] = G[i]; g[0] = g[0] | (p[0] & CI);
for (j = i+1; j < WIDTH; j = j+1)
tmp[j] = P[j]; // [[CITE]] Brent Kung Adder
GG = GG || &tmp[WIDTH-1:i]; // R. P. Brent and H. T. Kung, “A Regular Layout for Parallel Adders”,
// IEEE Transaction on Computers, Vol. C-31, No. 3, p. 260-264, March, 1982
// Main tree
for (i = 1; i <= $clog2(WIDTH); i = i+1) begin
for (j = 2**i - 1; j < WIDTH; j = j + 2**i) begin
k = j - 2**(i-1);
g[j] = g[j] | p[j] & g[k];
p[j] = p[j] & p[k];
end
end end
CO[0] = CI; // Inverse tree
for (i = 0; i < WIDTH; i = i+1) for (i = $clog2(WIDTH); i > 0; i = i-1) begin
CO[i+1] = G[i] | (P[i] & CO[i]); for (j = 2**i + 2**(i-1) - 1; j < WIDTH; j = j + 2**i) begin
k = j - 2**(i-1);
g[j] = g[j] | p[j] & g[k];
p[j] = p[j] & p[k];
end end
endmodule
module \$__lcu (P, G, CI, CO, PG, GG);
parameter WIDTH = 1;
function integer get_group_size;
begin
get_group_size = 4;
while (4 * get_group_size < WIDTH)
get_group_size = 4 * get_group_size;
end end
endfunction
input [WIDTH-1:0] P, G;
input CI;
output [WIDTH:0] CO;
output PG, GG;
genvar i;
generate
if (WIDTH <= 4) begin
\$__lcu_simple #(.WIDTH(WIDTH)) _TECHMAP_REPLACE_ (.P(P), .G(G), .CI(CI), .CO(CO), .PG(PG), .GG(GG));
end else begin
localparam GROUP_SIZE = get_group_size();
localparam GROUPS_NUM = (WIDTH + GROUP_SIZE - 1) / GROUP_SIZE;
wire [GROUPS_NUM-1:0] groups_p, groups_g;
wire [GROUPS_NUM:0] groups_ci;
for (i = 0; i < GROUPS_NUM; i = i+1) begin:V
localparam g_size = `MIN(GROUP_SIZE, WIDTH - i*GROUP_SIZE);
localparam g_offset = i*GROUP_SIZE;
wire [g_size:0] g_co;
\$__lcu #(.WIDTH(g_size)) g (.P(P[g_offset +: g_size]), .G(G[g_offset +: g_size]),
.CI(groups_ci[i]), .CO(g_co), .PG(groups_p[i]), .GG(groups_g[i]));
assign CO[g_offset+1 +: g_size] = g_co[1 +: g_size];
end end
\$__lcu_simple #(.WIDTH(GROUPS_NUM)) super_lcu (.P(groups_p), .G(groups_g), .CI(CI), .CO(groups_ci), .PG(PG), .GG(GG)); assign CO = {g, CI};
assign CO[0] = CI;
end
endgenerate
endmodule endmodule
module \$__alu_lookahead (A, B, CI, X, Y, CO, CS); module \$__alu_lookahead (A, B, CI, X, Y, CO, CS);