i2c_master_byte_ctrl.v

人民邮电出版社出版的《FPGA硬件接口设计实践》一书的代码

// synopsys translate_off
`include "timescale.v"
// synopsys translate_on

`include "i2c_master_defines.v"

module i2c_master_byte_ctrl (
	clk, rst, nReset, ena, clk_cnt, start, stop, read, write, ack_in, din,
	cmd_ack, ack_out, dout, i2c_busy, i2c_al, scl_i, scl_o, scl_oen, sda_i, sda_o, sda_oen );

	//
	// inputs & outputs
	//
	input clk;     // master clock
	input rst;     // synchronous active high reset
	input nReset;  // asynchronous active low reset
	input ena;     // core enable signal

	input [15:0] clk_cnt; // 4x SCL

	// control inputs
	input       start;
	input       stop;
	input       read;
	input       write;
	input       ack_in;
	input [7:0] din;

	// status outputs
	output       cmd_ack;
	reg cmd_ack;
	output       ack_out;
	reg ack_out;
	output       i2c_busy;
	output       i2c_al;
	output [7:0] dout;

	// I2C signals
	input  scl_i;
	output scl_o;
	output scl_oen;
	input  sda_i;
	output sda_o;
	output sda_oen;


	//
	// Variable declarations
	//

	// statemachine
	parameter [4:0] ST_IDLE  = 5'b0_0000;
	parameter [4:0] ST_START = 5'b0_0001;
	parameter [4:0] ST_READ  = 5'b0_0010;
	parameter [4:0] ST_WRITE = 5'b0_0100;
	parameter [4:0] ST_ACK   = 5'b0_1000;
	parameter [4:0] ST_STOP  = 5'b1_0000;

	// signals for bit_controller
	reg  [3:0] core_cmd;
	reg        core_txd;
	wire       core_ack, core_rxd;

	// signals for shift register
	reg [7:0] sr; //8bit shift register
	reg       shift, ld;

	// signals for state machine
	wire       go;
	reg  [2:0] dcnt;
	wire       cnt_done;

	//
	// Module body
	//

	// hookup bit_controller
	i2c_master_bit_ctrl bit_controller (
		.clk     ( clk      ),
		.rst     ( rst      ),
		.nReset  ( nReset   ),
		.ena     ( ena      ),
		.clk_cnt ( clk_cnt  ),
		.cmd     ( core_cmd ),
		.cmd_ack ( core_ack ),
		.busy    ( i2c_busy ),
		.al      ( i2c_al   ),
		.din     ( core_txd ),
		.dout    ( core_rxd ),
		.scl_i   ( scl_i    ),
		.scl_o   ( scl_o    ),
		.scl_oen ( scl_oen  ),
		.sda_i   ( sda_i    ),
		.sda_o   ( sda_o    ),
		.sda_oen ( sda_oen  )
	);

	// generate go-signal
	assign go = (read | write | stop) & ~cmd_ack;

	// assign dout output to shift-register
	assign dout = sr;

	// generate shift register
	always @(posedge clk or negedge nReset)
	  if (!nReset)
	    sr <= #1 8'h0;
	  else if (rst)
	    sr <= #1 8'h0;
	  else if (ld)
	    sr <= #1 din;
	  else if (shift)
	    sr <= #1 {sr[6:0], core_rxd};

	// generate counter
	always @(posedge clk or negedge nReset)
	  if (!nReset)
	    dcnt <= #1 3'h0;
	  else if (rst)
	    dcnt <= #1 3'h0;
	  else if (ld)
	    dcnt <= #1 3'h7;
	  else if (shift)
	    dcnt <= #1 dcnt - 3'h1;

	assign cnt_done = ~(|dcnt);

	//
	// state machine
	//
	reg [4:0] c_state; // synopsis enum_state

	always @(posedge clk or negedge nReset)
	  if (!nReset)
	    begin
	        core_cmd <= #1 `I2C_CMD_NOP;
	        core_txd <= #1 1'b0;
	        shift    <= #1 1'b0;
	        ld       <= #1 1'b0;
	        cmd_ack  <= #1 1'b0;
	        c_state  <= #1 ST_IDLE;
	        ack_out  <= #1 1'b0;
	    end
	  else if (rst | i2c_al)
	   begin
	       core_cmd <= #1 `I2C_CMD_NOP;
	       core_txd <= #1 1'b0;
	       shift    <= #1 1'b0;
	       ld       <= #1 1'b0;
	       cmd_ack  <= #1 1'b0;
	       c_state  <= #1 ST_IDLE;
	       ack_out  <= #1 1'b0;
	   end
	else
	  begin
	      // initially reset all signals
	      core_txd <= #1 sr[7];
	      shift    <= #1 1'b0;
	      ld       <= #1 1'b0;
	      cmd_ack  <= #1 1'b0;

	      case (c_state) // synopsis full_case parallel_case
	        ST_IDLE:
	          if (go)
	            begin
	                if (start)
	                  begin
	                      c_state  <= #1 ST_START;
	                      core_cmd <= #1 `I2C_CMD_START;
	                  end
	                else if (read)
	                  begin
	                      c_state  <= #1 ST_READ;
	                      core_cmd <= #1 `I2C_CMD_READ;
	                  end
	                else if (write)
	                  begin
	                      c_state  <= #1 ST_WRITE;
	                      core_cmd <= #1 `I2C_CMD_WRITE;
	                  end
	                else // stop
	                  begin
	                      c_state  <= #1 ST_STOP;
	                      core_cmd <= #1 `I2C_CMD_STOP;

	                      // generate command acknowledge signal
	                      cmd_ack  <= #1 1'b1;
	                  end

	                ld <= #1 1'b1;
	            end

	        ST_START:
	          if (core_ack)
	            begin
	                if (read)
	                  begin
	                      c_state  <= #1 ST_READ;
	                      core_cmd <= #1 `I2C_CMD_READ;
	                  end
	                else
	                  begin
	                      c_state  <= #1 ST_WRITE;
	                      core_cmd <= #1 `I2C_CMD_WRITE;
	                  end

	                ld <= #1 1'b1;
	            end

	        ST_WRITE:
	          if (core_ack)
	            if (cnt_done)
	              begin
	                  c_state  <= #1 ST_ACK;
	                  core_cmd <= #1 `I2C_CMD_READ;
	              end
	            else
	              begin
	                  c_state  <= #1 ST_WRITE;       // stay in same state
	                  core_cmd <= #1 `I2C_CMD_WRITE; // write next bit
	                  shift    <= #1 1'b1;
	              end

	        ST_READ:
	          if (core_ack)
	            begin
	                if (cnt_done)
	                  begin
	                      c_state  <= #1 ST_ACK;
	                      core_cmd <= #1 `I2C_CMD_WRITE;
	                  end
	                else
	                  begin
	                      c_state  <= #1 ST_READ;       // stay in same state
	                      core_cmd <= #1 `I2C_CMD_READ; // read next bit
	                  end

	                shift    <= #1 1'b1;
	                core_txd <= #1 ack_in;
	            end

	        ST_ACK:
	          if (core_ack)
	            begin
	               if (stop)
	                 begin
	                     c_state  <= #1 ST_STOP;
	                     core_cmd <= #1 `I2C_CMD_STOP;
	                 end
	               else
	                 begin
	                     c_state  <= #1 ST_IDLE;
	                     core_cmd <= #1 `I2C_CMD_NOP;
	                 end

	                 // assign ack_out output to bit_controller_rxd (contains last received bit)
	                 ack_out <= #1 core_rxd;

	                 // generate command acknowledge signal
	                 cmd_ack  <= #1 1'b1;

	                 core_txd <= #1 1'b1;
	             end
	           else
	             core_txd <= #1 ack_in;

	        ST_STOP:
	          if (core_ack)
	            begin
	                c_state  <= #1 ST_IDLE;
	                core_cmd <= #1 `I2C_CMD_NOP;
	            end

	      endcase
	  end
endmodule