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// Signed 40-bit streaming accumulator with 16-bit inputs
// File: HDL_Coding_Techniques/multipliers/multipliers4.v
//
// Source:
// https://www.xilinx.com/support/documentation/sw_manuals/xilinx2014_2/ug901-vivado-synthesis.pdf p.90
//
module macc # (parameter SIZEIN = 16, SIZEOUT = 40) (
input clk, ce, sload,
input signed [SIZEIN-1:0] a, b,
output signed [SIZEOUT-1:0] accum_out
);
// Declare registers for intermediate values
reg signed [SIZEIN-1:0] a_reg, b_reg;
reg sload_reg;
reg signed [2*SIZEIN-1:0] mult_reg;
reg signed [SIZEOUT-1:0] adder_out, old_result;
always @* /*(adder_out or sload_reg)*/ begin // Modification necessary to fix sim/synth mismatch
if (sload_reg)
old_result <= 0;
else
// 'sload' is now active (=low) and opens the accumulation loop.
// The accumulator takes the next multiplier output in
// the same cycle.
old_result <= adder_out;
end
always @(posedge clk)
if (ce)
begin
a_reg <= a;
b_reg <= b;
mult_reg <= a_reg * b_reg;
sload_reg <= sload;
// Store accumulation result into a register
adder_out <= old_result + mult_reg;
end
// Output accumulation result
assign accum_out = adder_out;
endmodule
// Adapted variant of above
module macc2 # (parameter SIZEIN = 16, SIZEOUT = 40) (
input clk,
input ce,
input rst,
input signed [SIZEIN-1:0] a, b,
output signed [SIZEOUT-1:0] accum_out,
output overflow
);
// Declare registers for intermediate values
reg signed [SIZEIN-1:0] a_reg, b_reg, a_reg2, b_reg2;
reg signed [2*SIZEIN-1:0] mult_reg = 0;
reg signed [SIZEOUT:0] adder_out = 0;
reg overflow_reg;
always @(posedge clk) begin
//if (ce)
begin
a_reg <= a;
b_reg <= b;
a_reg2 <= a_reg;
b_reg2 <= b_reg;
mult_reg <= a_reg2 * b_reg2;
// Store accumulation result into a register
adder_out <= adder_out + mult_reg;
overflow_reg <= overflow;
end
if (rst) begin
a_reg <= 0;
a_reg2 <= 0;
b_reg <= 0;
b_reg2 <= 0;
mult_reg <= 0;
adder_out <= 0;
overflow_reg <= 1'b0;
end
end
assign overflow = (adder_out >= 2**(SIZEOUT-1)) | overflow_reg;
// Output accumulation result
assign accum_out = overflow ? 2**(SIZEOUT-1)-1 : adder_out;
endmodule
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