mirror of
https://github.com/YosysHQ/yosys
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154 lines
3.7 KiB
Verilog
154 lines
3.7 KiB
Verilog
//-----------------------------------------------------
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// Design Name : uart
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// File Name : uart.v
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// Function : Simple UART
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// Coder : Deepak Kumar Tala
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//-----------------------------------------------------
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module uart (
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reset ,
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txclk ,
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ld_tx_data ,
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tx_data ,
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tx_enable ,
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tx_out ,
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tx_empty ,
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rxclk ,
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uld_rx_data ,
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rx_data ,
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rx_enable ,
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rx_in ,
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rx_empty
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);
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// Port declarations
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input reset ;
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input txclk ;
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input ld_tx_data ;
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input [7:0] tx_data ;
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input tx_enable ;
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output tx_out ;
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output tx_empty ;
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input rxclk ;
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input uld_rx_data ;
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output [7:0] rx_data ;
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input rx_enable ;
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input rx_in ;
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output rx_empty ;
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// Internal Variables
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reg [7:0] tx_reg ;
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reg tx_empty ;
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reg tx_over_run ;
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reg [3:0] tx_cnt ;
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reg tx_out ;
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reg [7:0] rx_reg ;
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reg [7:0] rx_data ;
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reg [3:0] rx_sample_cnt ;
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reg [3:0] rx_cnt ;
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reg rx_frame_err ;
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reg rx_over_run ;
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reg rx_empty ;
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reg rx_d1 ;
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reg rx_d2 ;
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reg rx_busy ;
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// UART RX Logic
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always @ (posedge rxclk or posedge reset)
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if (reset) begin
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rx_reg <= 0;
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rx_data <= 0;
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rx_sample_cnt <= 0;
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rx_cnt <= 0;
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rx_frame_err <= 0;
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rx_over_run <= 0;
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rx_empty <= 1;
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rx_d1 <= 1;
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rx_d2 <= 1;
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rx_busy <= 0;
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end else begin
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// Synchronize the asynch signal
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rx_d1 <= rx_in;
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rx_d2 <= rx_d1;
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// Uload the rx data
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if (uld_rx_data) begin
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rx_data <= rx_reg;
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rx_empty <= 1;
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end
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// Receive data only when rx is enabled
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if (rx_enable) begin
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// Check if just received start of frame
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if (!rx_busy && !rx_d2) begin
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rx_busy <= 1;
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rx_sample_cnt <= 1;
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rx_cnt <= 0;
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end
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// Start of frame detected, Proceed with rest of data
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if (rx_busy) begin
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rx_sample_cnt <= rx_sample_cnt + 1;
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// Logic to sample at middle of data
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if (rx_sample_cnt == 7) begin
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if ((rx_d2 == 1) && (rx_cnt == 0)) begin
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rx_busy <= 0;
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end else begin
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rx_cnt <= rx_cnt + 1;
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// Start storing the rx data
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if (rx_cnt > 0 && rx_cnt < 9) begin
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rx_reg[rx_cnt - 1] <= rx_d2;
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end
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if (rx_cnt == 9) begin
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rx_busy <= 0;
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// Check if End of frame received correctly
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if (rx_d2 == 0) begin
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rx_frame_err <= 1;
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end else begin
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rx_empty <= 0;
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rx_frame_err <= 0;
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// Check if last rx data was not unloaded,
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rx_over_run <= (rx_empty) ? 0 : 1;
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end
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end
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end
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end
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end
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end
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if (!rx_enable) begin
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rx_busy <= 0;
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end
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end
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// UART TX Logic
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always @ (posedge txclk or posedge reset)
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if (reset) begin
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tx_reg <= 0;
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tx_empty <= 1;
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tx_over_run <= 0;
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tx_out <= 1;
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tx_cnt <= 0;
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end else begin
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if (ld_tx_data) begin
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if (!tx_empty) begin
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tx_over_run <= 0;
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end else begin
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tx_reg <= tx_data;
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tx_empty <= 0;
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end
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end
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if (tx_enable && !tx_empty) begin
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tx_cnt <= tx_cnt + 1;
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if (tx_cnt == 0) begin
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tx_out <= 0;
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end
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if (tx_cnt > 0 && tx_cnt < 9) begin
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tx_out <= tx_reg[tx_cnt -1];
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end
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if (tx_cnt == 9) begin
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tx_out <= 1;
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tx_cnt <= 0;
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tx_empty <= 1;
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end
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end
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if (!tx_enable) begin
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tx_cnt <= 0;
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end
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end
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endmodule
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