| // SPDX-License-Identifier: Apache-2.0 |
| |
| `default_nettype none |
| /* |
| * PicoSoC - A simple example SoC using PicoRV32 |
| * |
| * Copyright (C) 2017 Clifford Wolf <clifford@clifford.at> |
| * |
| * Permission to use, copy, modify, and/or distribute this software for any |
| * purpose with or without fee is hereby granted, provided that the above |
| * copyright notice and this permission notice appear in all copies. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES |
| * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF |
| * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR |
| * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN |
| * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF |
| * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
| * |
| */ |
| |
| `timescale 1 ns / 1 ps |
| |
| /* tbuart --- mimic an external UART display, operating at 9600 baud */ |
| /* and accepting ASCII characters for display. */ |
| |
| /* To do: Match a known UART 3.3V 16x2 LCD display. However, it */ |
| /* should be possible on a testing system to interface to the UART */ |
| /* pins on a Raspberry Pi, also running at 3.3V. */ |
| |
| module tbuart ( |
| input ser_rx |
| ); |
| reg [3:0] recv_state; |
| reg [2:0] recv_divcnt; |
| reg [7:0] recv_pattern; |
| reg [8*50-1:0] recv_buf_data; // 50 characters. Increase as needed for tests. |
| |
| reg clk; |
| |
| initial begin |
| clk <= 1'b0; |
| recv_state <= 0; |
| recv_divcnt <= 0; |
| recv_pattern <= 0; |
| recv_buf_data <= 0; |
| end |
| |
| // NOTE: Running at 3.0us clock period @ 5 clocks per bit = 15.0us per |
| // bit ~= 64 kbaud. Not tuned to any particular UART. Most run at |
| // 9600 baud default and will bounce up to higher baud rates when |
| // passed specific command words. |
| |
| always #1500 clk <= (clk === 1'b0); |
| |
| always @(posedge clk) begin |
| recv_divcnt <= recv_divcnt + 1; |
| case (recv_state) |
| 0: begin |
| if (!ser_rx) |
| recv_state <= 1; |
| recv_divcnt <= 0; |
| end |
| 1: begin |
| if (2*recv_divcnt > 3'd3) begin |
| recv_state <= 2; |
| recv_divcnt <= 0; |
| end |
| end |
| 10: begin |
| if (recv_divcnt > 3'd3) begin |
| // 0x0a = '\n' |
| if (recv_pattern == 8'h0a) begin |
| $display("output: %s", recv_buf_data); |
| end else begin |
| recv_buf_data <= {recv_buf_data, recv_pattern}; |
| end |
| recv_state <= 0; |
| end |
| end |
| default: begin |
| if (recv_divcnt > 3'd3) begin |
| recv_pattern <= {ser_rx, recv_pattern[7:1]}; |
| recv_state <= recv_state + 1; |
| recv_divcnt <= 0; |
| end |
| end |
| endcase |
| end |
| |
| endmodule |