rtl/gfx: reimplement multiplier as a much smaller mat-vec pipeline

1 files changed, 55 insertions, 0 deletions

diff --git a/rtl/gfx/fold_flow.sv b/rtl/gfx/fold_flow.sv
new file mode 100644
index 0000000..718786e
--- /dev/null
+++ b/rtl/gfx/fold_flow.sv
@@ -0,0 +1,55 @@
+`include "gfx/gfx_defs.sv"
+
+module fold_flow
+(
+	input  logic  clk,
+	              rst_n,
+
+	input  logic  in_valid,
+	              out_ready,
+
+	output logic  in_ready,
+	              out_valid,
+	              stall,
+	              feedback,
+	              feedback_last
+);
+
+	index4 rounds[`FP_ADD_STAGES], last_round;
+
+	assign stall = out_valid && !out_ready;
+	assign in_ready = !stall && !feedback;
+	assign out_valid = last_round == `INDEX4_MAX;
+
+	assign feedback = last_round[1] ^ last_round[0];
+	assign feedback_last = last_round[1];
+
+	assign last_round = rounds[`FP_ADD_STAGES - 1];
+
+	always_ff @(posedge clk or negedge rst_n)
+		if (!rst_n)
+			rounds[0] <= `INDEX4_MIN;
+		else if (!stall)
+			unique case (last_round)
+				2'b01:
+					rounds[0] <= 2'b10;
+
+				2'b10: 
+					rounds[0] <= 2'b11;
+
+				2'b00, 2'b11:
+					rounds[0] <= {1'b0, in_valid};
+			endcase
+
+	genvar i;
+	generate
+		for (i = 1; i < `FP_ADD_STAGES; ++i) begin: pipeline
+			always_ff @(posedge clk or negedge rst_n)
+				if (!rst_n)
+					rounds[i] <= `INDEX4_MIN;
+				else if (in_ready)
+					rounds[i] <= rounds[i - 1];
+		end
+	endgenerate
+
+endmodule