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tinyriscv/rtl/perips/uart.v

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rtl: add uart rx function Signed-off-by: liangkangnan <liangkangnan@163.com>
2020-06-26 14:40:44 +00:00
/*
Copyright 2020 Blue Liang, liangkangnan@163.com
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
// 串口模块(默认: 115200, 8 N 1)
module uart(
input wire clk,
input wire rst,
input wire we_i,
input wire req_i,
input wire[31:0] addr_i,
input wire[31:0] data_i,
output reg[31:0] data_o,
output reg ack_o,
output wire tx_pin,
input wire rx_pin
);
// 50MHz时钟，波特率115200bps对应的分频系数
localparam BAUD_115200 = 32'h1B8;
localparam S_IDLE = 4'b0001;
localparam S_START = 4'b0010;
localparam S_SEND_BYTE = 4'b0100;
localparam S_STOP = 4'b1000;
reg tx_data_valid;
reg tx_data_ready;
reg[3:0] state;
reg[15:0] cycle_cnt;
reg[3:0] bit_cnt;
reg[7:0] tx_data;
reg tx_reg;
reg rx_q0;
reg rx_q1;
wire rx_negedge;
reg rx_start; // RX使能
reg[3:0] rx_clk_edge_cnt; // clk时钟沿的个数
reg rx_clk_edge_level; // clk沿电平
reg rx_done;
reg[15:0] rx_clk_cnt;
reg[15:0] rx_div_cnt;
reg[7:0] rx_data;
reg rx_over;
localparam UART_CTRL = 8'h0;
localparam UART_STATUS = 8'h4;
localparam UART_BAUD = 8'h8;
localparam UART_TXDATA = 8'hc;
localparam UART_RXDATA = 8'h10;
// addr: 0x00
// rw. bit[0]: tx enable, 1 = enable, 0 = disable
// rw. bit[1]: rx enable, 1 = enable, 0 = disable
reg[31:0] uart_ctrl;
// addr: 0x04
// ro. bit[0]: tx busy, 1 = busy, 0 = idle
// rw. bit[1]: rx over, 1 = over, 0 = receiving
// must check this bit before tx data
reg[31:0] uart_status;
// addr: 0x08
// rw. clk div
reg[31:0] uart_baud;
// addr: 0x10
// ro. rx data
reg[31:0] uart_rx;
assign tx_pin = tx_reg;
// 写寄存器
always @ (posedge clk) begin
if (rst == 1'b0) begin
uart_ctrl <= 32'h0;
uart_status <= 32'h0;
uart_rx <= 32'h0;
uart_baud <= BAUD_115200;
tx_data_valid <= 1'b0;
end else begin
if (we_i == 1'b1) begin
case (addr_i[7:0])
UART_CTRL: begin
uart_ctrl <= data_i;
end
UART_BAUD: begin
uart_baud <= data_i;
end
UART_STATUS: begin
uart_status[1] <= data_i[1];
end
UART_TXDATA: begin
if (uart_ctrl[0] == 1'b1 && uart_status[0] == 1'b0) begin
tx_data <= data_i[7:0];
uart_status[0] <= 1'b1;
tx_data_valid <= 1'b1;
end
end
endcase
end else begin
tx_data_valid <= 1'b0;
if (tx_data_ready == 1'b1) begin
uart_status[0] <= 1'b0;
end
if (uart_ctrl[1] == 1'b1) begin
if (rx_over == 1'b1) begin
uart_status[1] <= 1'b1;
uart_rx <= {24'h0, rx_data};
end
end
end
end
end
// 读寄存器
always @ (*) begin
if (rst == 1'b0) begin
data_o = 32'h0;
end else begin
case (addr_i[7:0])
UART_CTRL: begin
data_o = uart_ctrl;
end
UART_STATUS: begin
data_o = uart_status;
end
UART_BAUD: begin
data_o = uart_baud;
end
UART_RXDATA: begin
data_o = uart_rx;
end
default: begin
data_o = 32'h0;
end
endcase
end
end
// *************************** TX发送 ****************************
always @ (posedge clk) begin
if (rst == 1'b0) begin
state <= S_IDLE;
cycle_cnt <= 16'd0;
tx_reg <= 1'b0;
bit_cnt <= 4'd0;
tx_data_ready <= 1'b0;
end else begin
if (state == S_IDLE) begin
tx_reg <= 1'b1;
tx_data_ready <= 1'b0;
if (tx_data_valid == 1'b1) begin
state <= S_START;
cycle_cnt <= 16'd0;
bit_cnt <= 4'd0;
tx_reg <= 1'b0;
end
end else begin
cycle_cnt <= cycle_cnt + 16'd1;
if (cycle_cnt == uart_baud[15:0]) begin
cycle_cnt <= 16'd0;
case (state)
S_START: begin
tx_reg <= tx_data[bit_cnt];
state <= S_SEND_BYTE;
bit_cnt <= bit_cnt + 4'd1;
end
S_SEND_BYTE: begin
bit_cnt <= bit_cnt + 4'd1;
if (bit_cnt == 4'd8) begin
state <= S_STOP;
tx_reg <= 1'b1;
end else begin
tx_reg <= tx_data[bit_cnt];
end
end
S_STOP: begin
tx_reg <= 1'b1;
state <= S_IDLE;
tx_data_ready <= 1'b1;
end
endcase
end
end
end
end
// *************************** RX接收 ****************************
// 下降沿检测(检测起始信号)
assign rx_negedge = rx_q1 && ~rx_q0;
always @ (posedge clk) begin
if (rst == 1'b0) begin
rx_q0 <= 1'b0;
rx_q1 <= 1'b0;
end else begin
rx_q0 <= rx_pin;
rx_q1 <= rx_q0;
end
end
// 开始接收数据信号，接收期间一直有效
always @ (posedge clk) begin
if (rst == 1'b0) begin
rx_start <= 1'b0;
end else begin
if (uart_ctrl[1]) begin
if (rx_negedge) begin
rx_start <= 1'b1;
end else if (rx_clk_edge_cnt == 4'd9) begin
rx_start <= 1'b0;
end
end else begin
rx_start <= 1'b0;
end
end
end
always @ (posedge clk) begin
if (rst == 1'b0) begin
rx_div_cnt <= 16'h0;
end else begin
// 第一个时钟沿只需波特率分频系数的一半
if (rx_start == 1'b1 && rx_clk_edge_cnt == 4'h0) begin
rx_div_cnt <= {1'b0, uart_baud[15:1]};
end else begin
rx_div_cnt <= uart_baud[15:0];
end
end
end
// 对时钟进行计数
always @ (posedge clk) begin
if (rst == 1'b0) begin
rx_clk_cnt <= 16'h0;
end else if (rx_start == 1'b1) begin
// 计数达到分频值
if (rx_clk_cnt == rx_div_cnt) begin
rx_clk_cnt <= 16'h0;
end else begin
rx_clk_cnt <= rx_clk_cnt + 1'b1;
end
end else begin
rx_clk_cnt <= 16'h0;
end
end
// 每当时钟计数达到分频值时产生一个上升沿脉冲
always @ (posedge clk) begin
if (rst == 1'b0) begin
rx_clk_edge_cnt <= 4'h0;
rx_clk_edge_level <= 1'b0;
end else if (rx_start == 1'b1) begin
// 计数达到分频值
if (rx_clk_cnt == rx_div_cnt) begin
// 时钟沿个数达到最大值
if (rx_clk_edge_cnt == 4'd9) begin
rx_clk_edge_cnt <= 4'h0;
rx_clk_edge_level <= 1'b0;
end else begin
// 时钟沿个数加1
rx_clk_edge_cnt <= rx_clk_edge_cnt + 1'b1;
// 产生上升沿脉冲
rx_clk_edge_level <= 1'b1;
end
end else begin
rx_clk_edge_level <= 1'b0;
end
end else begin
rx_clk_edge_cnt <= 4'h0;
rx_clk_edge_level <= 1'b0;
end
end
// bit序列
always @ (posedge clk) begin
if (rst == 1'b0) begin
rx_data <= 8'h0;
rx_over <= 1'b0;
end else begin
if (rx_start == 1'b1) begin
// 上升沿
if (rx_clk_edge_level == 1'b1) begin
case (rx_clk_edge_cnt)
// 起始位
1: begin
end
// 数据位
2, 3, 4, 5, 6, 7, 8, 9: begin
rx_data <= rx_data | (rx_pin << (rx_clk_edge_cnt - 2));
// 最后一位接收完成，置位接收完成标志
if (rx_clk_edge_cnt == 4'h9) begin
rx_over <= 1'b1;
end
end
endcase
end
end else begin
rx_data <= 8'h0;
rx_over <= 1'b0;
end
end
end
endmodule