diff --git a/src/spi_core.v b/src/spi_core.v
new file mode 100644
index 0000000..1f4b9a1
--- /dev/null
+++ b/src/spi_core.v
@@ -0,0 +1,125 @@
+	
+module spi_core(
+	input clk, rst,
+	
+	input sck, sdi, sdo, ncs,
+	
+	output reg cs_rising,
+	output reg cs_falling,
+	output reg data[15:0],
+	output reg data_valid
+);
+
+reg data_release_flag_sysclk;
+
+reg [15:0] rxbuf_sck;
+reg [15:0] data_reg_sck;
+reg data_good_flag_sck;
+always @(posedge sck or posedge ncs) begin
+	if (ncs) begin /* asynchronous reset */
+		data_reg_sck <= 16'h0001;
+		data_good_flag_sck <= 0;
+		
+	end else begin
+		if (data_reg_sck[15]) begin
+			rxbuf_sck <= {data_reg_sck[14:0], sdi};
+			data_reg_sck <= 16'h0001;
+			data_good_flag_sck <= 1;
+			
+		end else begin
+			data_reg_sck <= {data_reg_sck[14:0], sdi};
+		end
+	end
+end
+
+reg cs_rising_sysclk;
+reg cs_falling_sysclk;
+reg last_cs_sysclk;
+reg [1:0] data_good_flag_sysclk;
+always @(posedge clk) begin
+	if (rst) begin
+		last_cs_sysclk <= cs;
+		cs_rising <= 0;
+		cs_falling <= 0;
+		data_valid <= 0;
+		data <= 0;
+		data_release_flag_sysclk <= 0;
+		data_good_flag_sysclk <= 0;
+	
+	end else begin
+		data_good_flag_sysclk <= {data-good_flag_sysclk[0], data_good_flag_sck};
+		
+		if (last_cs_sysclk = 0 && cs == 1) begin
+			cs_rising <= 1;
+			cs_falling <= 0;
+		end else begin if (last_cs_sysclk = 1 && cs == 0) begin
+			cs_rising <= 0;
+			cs_falling <= 1;
+		end
+		
+		if (!last_cs_sysclk && data_good_flag_sysclk[0] && data_good_flag_sysclk[1]) begin
+			data <= rxbuf_sck;
+			data_release_flag_sysclk <= 1;
+		end
+	end
+end
+
+endmodule
+
+module cdc_reg (
+	input in_clk, in_rst,
+	input [WORDSIZE-1:0] in_data,
+	input in_data_valid,
+	
+	input out_clk, out_rst,
+	output reg [WORDSIZE-1:0] out_data,
+	output reg out_data_valid,
+);
+
+parameter WORDSIZE = 16;
+
+reg [2:0] wr_flags_in;
+reg [WORDSIZE-1:0] reg_in [0:2];
+always @(posedge in_clk, posedge in_rst) begin
+	if (in_rst) begin
+		wr_flags_in <= 3'b000;
+		regs_in[0] <= 0;
+		regs_in[1] <= 0;
+		regs_in[2] <= 0;
+		
+	end else begin
+		case (regs_in)
+		3'b001: 		begin regs_in[1] <= in_data; wr_flags_in <= 3'b010; end
+		3'b010: 		begin regs_in[2] <= in_data; wr_flags_in <= 3'b100; end
+		3'b100, 3'b000: begin regs_in[0] <= in_data; wr_flags_in <= 3'b001; end
+		endcase
+	end
+end
+
+reg [2:0] wr_flags_out [0:1];
+always @(posedge out_clk) begin
+	if (out_rst) begin
+		wr_flags_out[0] <= 3'b000;
+		wr_flags_out[1] <= 3'b000;
+	
+	end else begin
+		wr_flags_out[0] <= wr_flags_in;
+		wr_flags_out[1] <= wr_flags_out[0];
+		out_data_valid <= 0;
+		
+		if (wr_flags_out[0][0] && !wr_flags_out[1][0]) begin
+			out_data <= regs_in[0];
+			out_data_valid <= 1;
+			
+		end else if (wr_flags_out[0][1] && !wr_flags_out[1][1]) begin
+			out_data <= regs_in[1];
+			out_data_valid <= 1;
+			
+		end else if (wr_flags_out[0][2] && !wr_flags_out[1][2]) begin
+			out_data <= regs_in[2];
+			out_data_valid <= 1;
+		end
+	end
+end
+
+endmodule
\ No newline at end of file
diff --git a/test_bench/spi_core_tb.v b/test_bench/spi_core_tb.v
new file mode 100644
index 0000000..e69de29