1 files changed, 86 insertions, 0 deletions
diff --git a/src/ksa.sv b/src/ksa.sv
new file mode 100644
index 0000000..0d79899
--- /dev/null
+++ b/src/ksa.sv
@@ -0,0 +1,86 @@
+module ksa(clk, rst_n, en, rdy, key, addr, rddata, wrdata, wren);
+
+	input logic clk, rst_n, en;
+	input logic [7:0] rddata;
+	input logic [23:0] key;
+	output logic rdy, wren;
+	output logic [7:0] addr, wrdata;
+
+	logic started, wren_next;
+	logic [2:0] state, state_next;
+	logic [7:0] i, j, i_next, j_next, wrdata_next, addr_next, si, si_next;
+
+	always_comb begin: ksa_logic
+		state_next = state + 1;
+		i_next = i;
+		j_next = j;
+		addr_next = i;
+		wrdata_next = 8'b0;
+		wren_next = 1'b0;
+		si_next = si;
+		case (state)
+			/* Fetch s[i]. */
+			3'd0: begin end
+			/* s[i] is now in rddata. */
+			3'd1: begin end
+			/* Compute j; fetch s[j]; latch s[i] from rddata. */
+			3'd2: begin
+				if (i % 3 == 2'd0)
+					j_next = j + rddata + key[23:16];
+				else if (i % 3 == 2'd1)
+					j_next = j + rddata + key[15:8];
+				else
+					j_next = j + rddata + key[7:0];
+				addr_next = j_next;
+				si_next = rddata;
+			end
+			/* s[j] is now in rddata. */
+			3'd3: begin end
+			/* Store rddata (s[j]) to address i. */
+			3'd4: begin
+				wrdata_next = rddata;
+				wren_next = 1'b1;
+			end
+			/* Store si (s[i]) to address j; increment i; reset. */
+			3'd5: begin
+				state_next = 3'd0;
+				i_next = i + 1;
+				addr_next = j;
+				wrdata_next = si;
+				wren_next = 1'b1;
+			end
+		endcase
+	end: ksa_logic
+
+	always_ff @(posedge clk) begin: ksa_state_machine
+		if (~rst_n) begin
+			rdy <= 1'b1;
+			started <= 1'b0;
+			state <= 3'd0;
+			i <= 8'b0;
+			j <= 8'b0;
+			addr <= 8'b0;
+		end else if (rdy && en) begin
+			rdy <= 1'b0;
+			started <= 1'b1;
+			state <= 3'd0;
+			i <= 8'b0;
+			j <= 8'b0;
+			addr <= 8'b0;
+			wren <= 1'b0;
+		end else if (started) begin
+			state <= state_next;
+			i <= i_next;
+			j <= j_next;
+			addr <= addr_next;
+			wrdata <= wrdata_next;
+			wren <= wren_next;
+			si <= si_next;
+			if ((i == 8'd255) && (state == 3'd5)) begin
+				rdy <= 1'b1;
+				started <= 1'b0;
+			end
+		end
+	end: ksa_state_machine
+
+endmodule: ksa