diff options
Diffstat (limited to 'techlibs/common')
-rw-r--r-- | techlibs/common/simlib.v | 44 |
1 files changed, 36 insertions, 8 deletions
diff --git a/techlibs/common/simlib.v b/techlibs/common/simlib.v index a424d3089..7845a3fed 100644 --- a/techlibs/common/simlib.v +++ b/techlibs/common/simlib.v @@ -532,14 +532,26 @@ endmodule // -------------------------------------------------------- +// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---| +//- +//- $lcu (P, G, CI, CO) +//- +//- Lookahead carry unit +//- A building block dedicated to fast computation of carry-bits used in binary +//- arithmetic operations. By replacing the ripple carry structure used in full-adder +//- blocks, the more significant bits of the sum can be expected to be computed more +//- quickly. +//- Typically created during `techmap` of $alu cells (see the "_90_alu" rule in +//- +/techmap.v). module \$lcu (P, G, CI, CO); parameter WIDTH = 1; -input [WIDTH-1:0] P, G; -input CI; +input [WIDTH-1:0] P; // Propagate +input [WIDTH-1:0] G; // Generate +input CI; // Carry-in -output reg [WIDTH-1:0] CO; +output reg [WIDTH-1:0] CO; // Carry-out integer i; always @* begin @@ -555,6 +567,17 @@ endmodule // -------------------------------------------------------- +// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---| +//- +//- $alu (A, B, CI, BI, X, Y, CO) +//- +//- Arithmetic logic unit. +//- A building block supporting both binary addition/subtraction operations, and +//- indirectly, comparison operations. +//- Typically created by the `alumacc` pass, which transforms: +//- $add, $sub, $lt, $le, $ge, $gt, $eq, $eqx, $ne, $nex +//- cells into this $alu cell. +//- module \$alu (A, B, CI, BI, X, Y, CO); parameter A_SIGNED = 0; @@ -563,12 +586,16 @@ parameter A_WIDTH = 1; parameter B_WIDTH = 1; parameter Y_WIDTH = 1; -input [A_WIDTH-1:0] A; -input [B_WIDTH-1:0] B; -output [Y_WIDTH-1:0] X, Y; +input [A_WIDTH-1:0] A; // Input operand +input [B_WIDTH-1:0] B; // Input operand +output [Y_WIDTH-1:0] X; // A xor B (sign-extended, optional B inversion, + // used in combination with + // reduction-AND for $eq/$ne ops) +output [Y_WIDTH-1:0] Y; // Sum -input CI, BI; -output [Y_WIDTH-1:0] CO; +input CI; // Carry-in (set for $sub) +input BI; // Invert-B (set for $sub) +output [Y_WIDTH-1:0] CO; // Carry-out wire [Y_WIDTH-1:0] AA, BB; @@ -584,6 +611,7 @@ endgenerate wire y_co_undef = ^{A, A, B, B, CI, CI, BI, BI}; assign X = AA ^ BB; +// Full adder assign Y = (AA + BB + CI) ^ {Y_WIDTH{y_co_undef}}; function get_carry; |