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[/] [s6soc/] [trunk/] [rtl/] [rxuart.v] - Rev 31
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//////////////////////////////////////////////////////////////////////////////// // // Filename: rxuart.v // // Project: CMod S6 System on a Chip, ZipCPU demonstration project // // Purpose: Receive and decode inputs from a single UART line. // // // To interface with this module, connect it to your system clock, // pass it the 32 bit setup register (defined below) and the UART // input. When data becomes available, the o_wr line will be asserted // for one clock cycle. On parity or frame errors, the o_parity_err // or o_frame_err lines will be asserted. Likewise, on a break // condition, o_break will be asserted. These lines are self clearing. // // There is a synchronous reset line, logic high. // // Now for the setup register. The register is 32 bits, so that this // UART may be set up over a 32-bit bus. // // i_setup[29:28] Indicates the number of data bits per word. This will // either be 2'b00 for an 8-bit word, 2'b01 for a 7-bit word, 2'b10 // for a six bit word, or 2'b11 for a five bit word. // // i_setup[27] Indicates whether or not to use one or two stop bits. // Set this to one to expect two stop bits, zero for one. // // i_setup[26] Indicates whether or not a parity bit exists. Set this // to 1'b1 to include parity. // // i_setup[25] Indicates whether or not the parity bit is fixed. Set // to 1'b1 to include a fixed bit of parity, 1'b0 to allow the // parity to be set based upon data. (Both assume the parity // enable value is set.) // // i_setup[24] This bit is ignored if parity is not used. Otherwise, // in the case of a fixed parity bit, this bit indicates whether // mark (1'b1) or space (1'b0) parity is used. Likewise if the // parity is not fixed, a 1'b1 selects even parity, and 1'b0 // selects odd. // // i_setup[23:0] Indicates the speed of the UART in terms of clocks. // So, for example, if you have a 200 MHz clock and wish to // run your UART at 9600 baud, you would take 200 MHz and divide // by 9600 to set this value to 24'd20834. Likewise if you wished // to run this serial port at 115200 baud from a 200 MHz clock, // you would set the value to 24'd1736 // // Thus, to set the UART for the common setting of an 8-bit word, // one stop bit, no parity, and 115200 baud over a 200 MHz clock, you // would want to set the setup value to: // // 32'h0006c8 // For 115,200 baud, 8 bit, no parity // 32'h005161 // For 9600 baud, 8 bit, no parity // // // // Creator: Dan Gisselquist, Ph.D. // Gisselquist Technology, LLC // //////////////////////////////////////////////////////////////////////////////// // // Copyright (C) 2015-2016, Gisselquist Technology, LLC // // This program is free software (firmware): you can redistribute it and/or // modify it under the terms of the GNU General Public License as published // by the Free Software Foundation, either version 3 of the License, or (at // your option) any later version. // // This program is distributed in the hope that it will be useful, but WITHOUT // ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License // for more details. // // You should have received a copy of the GNU General Public License along // with this program. (It's in the $(ROOT)/doc directory, run make with no // target there if the PDF file isn't present.) If not, see // <http://www.gnu.org/licenses/> for a copy. // // License: GPL, v3, as defined and found on www.gnu.org, // http://www.gnu.org/licenses/gpl.html // // //////////////////////////////////////////////////////////////////////////////// // // // States: (@ baud counter == 0) // 0 First bit arrives // ..7 Bits arrive // 8 Stop bit (x1) // 9 Stop bit (x2) /// c break condition // d Waiting for the channel to go high // e Waiting for the reset to complete // f Idle state `define RXU_BIT_ZERO 4'h0 `define RXU_BIT_ONE 4'h1 `define RXU_BIT_TWO 4'h2 `define RXU_BIT_THREE 4'h3 `define RXU_BIT_FOUR 4'h4 `define RXU_BIT_FIVE 4'h5 `define RXU_BIT_SIX 4'h6 `define RXU_BIT_SEVEN 4'h7 `define RXU_PARITY 4'h8 `define RXU_STOP 4'h9 `define RXU_SECOND_STOP 4'ha // Unused 4'hb // Unused 4'hc `define RXU_BREAK 4'hd `define RXU_RESET_IDLE 4'he `define RXU_IDLE 4'hf module rxuart(i_clk, i_reset, i_setup, i_uart, o_wr, o_data, o_break, o_parity_err, o_frame_err, o_ck_uart); // parameter // CLOCKS_PER_BAUD = 25'd004340, // BREAK_CONDITION = CLOCKS_PER_BAUD * 12, // CLOCKS_PER_HALF_BAUD = CLOCKS_PER_BAUD/2; // 8 data bits, no parity, (at least 1) stop bit input i_clk, i_reset; input [29:0] i_setup; input i_uart; output reg o_wr; output reg [7:0] o_data; output reg o_break; output reg o_parity_err, o_frame_err; output wire o_ck_uart; wire [27:0] clocks_per_baud, break_condition, half_baud; wire [1:0] data_bits; wire use_parity, parity_even, dblstop, fixd_parity; reg [29:0] r_setup; assign clocks_per_baud = { 4'h0, r_setup[23:0] }; assign data_bits = r_setup[29:28]; assign dblstop = r_setup[27]; assign use_parity = r_setup[26]; assign fixd_parity = r_setup[25]; assign parity_even = r_setup[24]; assign break_condition = { r_setup[23:0], 4'h0 }; assign half_baud = { 5'h00, r_setup[23:1] }; reg q_uart, qq_uart, ck_uart; initial q_uart = 1'b0; initial qq_uart = 1'b0; initial ck_uart = 1'b0; always @(posedge i_clk) begin q_uart <= i_uart; qq_uart <= q_uart; ck_uart <= qq_uart; end assign o_ck_uart = ck_uart; reg [27:0] chg_counter; initial chg_counter = 28'h00; always @(posedge i_clk) if (i_reset) chg_counter <= 28'h00; else if (qq_uart != ck_uart) chg_counter <= 28'h00; else if (chg_counter < break_condition) chg_counter <= chg_counter + 1; always @(posedge i_clk) o_break <=((chg_counter >= break_condition)&&(~ck_uart))? 1'b1:1'b0; reg [3:0] state; reg [27:0] baud_counter; reg [7:0] data_reg; reg calc_parity; initial o_wr = 1'b0; initial state = `RXU_RESET_IDLE; initial o_parity_err = 1'b0; initial o_frame_err = 1'b0; // initial baud_counter = clocks_per_baud; always @(posedge i_clk) begin if (i_reset) begin o_wr <= 1'b0; o_data <= 8'h00; state <= `RXU_RESET_IDLE; baud_counter <= clocks_per_baud; // Set, not reset data_reg <= 8'h00; calc_parity <= 1'b0; o_parity_err <= 1'b0; o_frame_err <= 1'b0; end else if (state == `RXU_RESET_IDLE) begin r_setup <= i_setup; data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0; baud_counter <= clocks_per_baud-28'h01;// Set, not reset if ((ck_uart)&&(chg_counter >= break_condition)) // Goto idle state from a reset state <= `RXU_IDLE; else // Otherwise, stay in this condition 'til reset state <= `RXU_RESET_IDLE; calc_parity <= 1'b0; o_parity_err <= 1'b0; o_frame_err <= 1'b0; end else if ((~ck_uart)&&(chg_counter >= break_condition)) begin // We are in a break condition state <= `RXU_BREAK; o_wr <= 1'b0; o_data <= 8'h00; baud_counter <= clocks_per_baud-28'h01;// Set, not reset data_reg <= 8'h00; calc_parity <= 1'b0; o_parity_err <= 1'b0; o_frame_err <= 1'b0; r_setup <= i_setup; end else if (state == `RXU_BREAK) begin // Goto idle state following return ck_uart going high data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0; baud_counter <= clocks_per_baud - 28'h01; if (ck_uart) state <= `RXU_IDLE; else state <= `RXU_BREAK; calc_parity <= 1'b0; o_parity_err <= 1'b0; o_frame_err <= 1'b0; r_setup <= i_setup; end else if (state == `RXU_IDLE) begin // Idle state, independent of baud counter data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0; baud_counter <= clocks_per_baud - 28'h01; if ((ck_uart == 1'b0)&&(chg_counter > half_baud)) begin // We are in the center of a valid start bit case (data_bits) 2'b00: state <= `RXU_BIT_ZERO; 2'b01: state <= `RXU_BIT_ONE; 2'b10: state <= `RXU_BIT_TWO; 2'b11: state <= `RXU_BIT_THREE; endcase end else // Otherwise, just stay here in idle state <= `RXU_IDLE; calc_parity <= 1'b0; o_parity_err <= 1'b0; o_frame_err <= 1'b0; end else if (baud_counter == 0) begin baud_counter <= clocks_per_baud-28'h1; if (state < `RXU_BIT_SEVEN) begin // Data arrives least significant bit first. // By the time this is clocked in, it's what // you'll have. data_reg <= { ck_uart, data_reg[7:1] }; calc_parity <= calc_parity ^ ck_uart; o_data <= 8'h00; o_wr <= 1'b0; state <= state + 1; o_parity_err <= 1'b0; o_frame_err <= 1'b0; end else if (state == `RXU_BIT_SEVEN) begin data_reg <= { ck_uart, data_reg[7:1] }; calc_parity <= calc_parity ^ ck_uart; o_data <= 8'h00; o_wr <= 1'b0; state <= (use_parity) ? `RXU_PARITY:`RXU_STOP; o_parity_err <= 1'b0; o_frame_err <= 1'b0; end else if (state == `RXU_PARITY) begin if (fixd_parity) o_parity_err <= (ck_uart ^ parity_even); else o_parity_err <= ((parity_even && (calc_parity != ck_uart)) ||((~parity_even)&&(calc_parity==ck_uart))); state <= `RXU_STOP; o_frame_err <= 1'b0; end else if (state == `RXU_STOP) begin // Stop (or parity) bit(s) case (data_bits) 2'b00: o_data <= data_reg; 2'b01: o_data <= { 1'b0, data_reg[7:1] }; 2'b10: o_data <= { 2'b0, data_reg[7:2] }; 2'b11: o_data <= { 3'b0, data_reg[7:3] }; endcase o_wr <= 1'b1; // Pulse the write o_frame_err <= (~ck_uart); if (~ck_uart) state <= `RXU_RESET_IDLE; else if (dblstop) state <= `RXU_SECOND_STOP; else state <= `RXU_IDLE; // o_parity_err <= 1'b0; end else // state must equal RX_SECOND_STOP begin if (~ck_uart) begin o_frame_err <= 1'b1; state <= `RXU_RESET_IDLE; end else begin state <= `RXU_IDLE; o_frame_err <= 1'b0; end o_parity_err <= 1'b0; end end else begin o_wr <= 1'b0; // data_reg = data_reg baud_counter <= baud_counter - 28'd1; o_parity_err <= 1'b0; o_frame_err <= 1'b0; end end endmodule
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