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authorClifford Wolf <clifford@clifford.at>2014-08-18 00:03:33 +0200
committerClifford Wolf <clifford@clifford.at>2014-08-18 00:03:33 +0200
commit4b3834e0cc3c34b6845ab50ffd7e9fe396173e8d (patch)
tree0a920ce7e887243b5f4836710c166bf3965157ac
parentacb435b6cf583b6c18f405a9c92566c4e9fb85e5 (diff)
Replaced recursive lcu scheme with bk adder
-rw-r--r--techlibs/common/techmap.v92
1 files changed, 31 insertions, 61 deletions
diff --git a/techlibs/common/techmap.v b/techlibs/common/techmap.v
index 9bdff4f3..5bbe883e 100644
--- a/techlibs/common/techmap.v
+++ b/techlibs/common/techmap.v
@@ -285,80 +285,50 @@ module \$__alu_ripple (A, B, CI, X, Y, CO, CS);
endgenerate
endmodule
-module \$__lcu_simple (P, G, CI, CO, PG, GG);
- parameter WIDTH = 1;
+module \$__lcu (P, G, CI, CO);
+ parameter WIDTH = 2;
input [WIDTH-1:0] P, G;
input CI;
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;
- reg [WIDTH-1:0] tmp;
+ wire [1023:0] _TECHMAP_DO_ = "proc; opt -fast";
always @* begin
- PG = &P;
- GG = 0;
- for (i = 0; i < WIDTH; i = i+1) begin
- tmp = ~0;
- tmp[i] = G[i];
- for (j = i+1; j < WIDTH; j = j+1)
- tmp[j] = P[j];
- GG = GG || &tmp[WIDTH-1:i];
- end
-
- CO[0] = CI;
- for (i = 0; i < WIDTH; i = i+1)
- CO[i+1] = G[i] | (P[i] & CO[i]);
- 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;
+ p = P;
+ g = G;
+
+ // in almost all cases CI will be constant zero
+ g[0] = g[0] | (p[0] & CI);
+
+ // [[CITE]] Brent Kung Adder
+ // 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
- 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];
+ // Inverse tree
+ for (i = $clog2(WIDTH); i > 0; i = i-1) begin
+ 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
-
- \$__lcu_simple #(.WIDTH(GROUPS_NUM)) super_lcu (.P(groups_p), .G(groups_g), .CI(CI), .CO(groups_ci), .PG(PG), .GG(GG));
-
- assign CO[0] = CI;
end
- endgenerate
+ end
+
+ assign CO = {g, CI};
endmodule
module \$__alu_lookahead (A, B, CI, X, Y, CO, CS);