Yuqing li - config regs/baud rate

rtl/io/uart16550.sv

@@ -0,0 +1,171 @@
+`timescale 1ns / 1ps
+parameter FIFO_DEPTH = 16;
+//UART interface
+module UARTmodule(
+//clock to generate Baud rate
+input wire clk,
+//reset signal to initialize/clear registers
+input wire rst,
+//Axi-lite bus interface
+input  wire [31:0] CPU_to_UART, 
+output wire [31:0] UART_to_CPU,
+//Recieve/Transmit serial bit 
+input wire rx_i,
+output wire tx_o,
+//Interrupt for CPU to read
+output wire irq_o
+    );
+/*******************************BUS BIT FIELDS*****************************/
+    //CPU to UART internal signals for write
+    wire awvalid = CPU_to_UART [0];
+    wire wvalid = CPU_to_UART [1];
+    wire [2:0] awaddr = CPU_to_UART [4:2];
+    wire bready = CPU_to_UART [5];
+    wire [7:0] wdata = CPU_to_UART [13:6];
+    //UART to CPU internal signals for write
+    wire awready;
+    wire wready;
+    wire bvalid;
+    wire [1:0] bresp;
+    //CPU to UART internal signals for read
+    wire arvalid = CPU_to_UART [15];
+    wire [2:0] araddr = CPU_to_UART [18:16];
+    wire rready = CPU_to_UART [19];
+    //UART to CPU internal signals for read
+    wire arready;
+    wire rvalid;
+    wire [1:0] rresp;
+    wire [7:0] rdata;
+    //assign write-related bits
+
+/**************************REGISTERS & FIFO QUEUE*************************/ 
+    localparam ADDR_WIDTH = $clog2(FIFO_DEPTH);
+    reg [7:0] THR;
+    reg [7:0] RBR;
+    reg [7:0] IER;
+    reg [7:0] ISR;
+    reg [7:0] FCR;
+    reg [7:0] LCR;
+    reg [7:0] LSR;
+    reg [7:0] MCR;
+    reg [7:0] MSR;
+    reg [7:0] SPR;
+    reg [7:0] DLL;
+    reg [7:0] DLM;
+    reg [7:0] PSD;
+    //FIFO mem stack, pointers and status
+    reg [7:0] fifo_mem [0:FIFO_DEPTH-1];
+    reg [ADDR_WIDTH-1:0] waddr_ptr;
+    reg [ADDR_WIDTH-1:0] raddr_ptr;
+    reg [ADDR_WIDTH:0] count;
+    wire fifo_full  = (count == FIFO_DEPTH);
+    wire fifo_empty = (count == 0);
+
+/****************************CONFIG REGS*******************************/
+    always @(posedge clk or posedge rst) begin
+        if (rst) begin //reset registers to its reset values
+            THR <= 8'h00;
+            RBR <= 8'h00;
+            IER <= 8'h00;
+            ISR <= 8'h01;
+            FCR <= 8'h00; //the datasheet reset value is 0x00? 
+            LCR <= 8'h00;
+            LSR <= 8'h60;
+            MCR <= 8'h00;
+            MSR <= 8'h00;
+            SPR <= 8'h00;
+            DLL <= 8'h01;
+            DLM <= 8'h01;
+            PSD <= 8'h00;
+        end
+        else begin //to handle CPU writes 
+            if  (awvalid && wvalid && awready && wready) begin 
+                case (awaddr) //address of the register
+                    3'b000: begin 
+                        if (LCR[7]==1'b0)// check DLAB = 0 -> THR, DLAB = 1 -> DLL
+                            THR <= wdata; // write data to be transmitted
+                        else
+                            DLL <= wdata; // baudrate low byte
+                    end
+                    3'b001: begin
+                        if (LCR[7]==1'b0)
+                            IER <= wdata; // enable interrupt 
+                        else
+                            DLM <= wdata; // baudrate high byte
+                    end 
+                    3'b010: FCR <= wdata; //FIFO control
+                    3'b011: LCR <= wdata; //Line Control
+                    3'b100: MCR <= wdata; //Modern control
+                    3'b101: begin 
+                        if (LCR [7] ==1'b1) 
+                            PSD <= {4'b0000, wdata[3:0]}; //prescaler division
+                    end
+                    3'b111: SPR <= wdata; // Scratch Pad 
+                endcase
+            end
+        end
+    end
+
+/**************************BAUD RATE CALC******************************/
+wire [15:0] baud_divisor = {DLM,DLL};   //16-bit divisor from DLM & DLL
+    wire [3:0] psd_value = PSD [3:0];       // the lower 4-bit are used
+
+    //clk/(16*(PSD+1)*baud_divisor) -- counter holder for the math 
+    reg [3:0] PSD_counter;         //for PSD+1
+    reg [15:0] divisor_counter;    //divides by divisor
+    reg [3:0] multi_by_16;         //divides by 16
+    reg baud_tick;                 //final baud pulse
+
+    always @(posedge clk_i or negedge rst_ni) begin 
+        if (rst_ni) begin //reseting the counter
+            PSD_counter <= 4'd0;
+            divisor_counter <= 16'd0;
+            multi_by_16 <= 4'd0;
+            baud_tick <= 1'b0; 
+        end 
+        else begin
+            baud_tick <= 1'b0; //default setting counting clock cycle
+
+            if (PSD_counter == psd_value) begin // divides by PSD + 1 
+                PSD_counter <= 4'd0;
+            end 
+            else begin 
+                PSD_counter <= PSD_counter + 1'b1; 
+            end
+
+            if (divisor_counter == baud_divisor - 1) begin //divides by divisor
+                divisor_counter <= 16'd0;
+            end
+            else begin
+                divisor_counter <= divisor_counter + 1'b1; 
+            end 
+
+            if (multi_by_16 == 4'd15) begin // divide by 16 
+                multi_by_16 <= 16'd0;
+                baud_tick <= 1'b1; 
+            end else begin
+                multi_by_16 <= multi_by_16 + 1'b1; 
+            end 
+        end
+     end
+/***************************TRANSMIT tx_o******************************/
+// FIFO -> shift register -> serial output
+
+/***************************RECEIVE rx_i*******************************/
+// Serial input -> shift register -> FIFO
+
+/***************************UART to CPU********************************/
+// AXI-Lite read/write response
+// THR, RBR, FIFO status, line status
+
+/***************************INTERRUPT irq_o****************************/
+// RX/TX interrupts based on IER and FIFO/line status
+
+/***************************FIFO MANAGEMENT****************************/
+// Push/pop data, update pointers and count
+
+/***************************ERROR DETECTION***************************/
+// Parity, framing, overrun errors
+endmodule
+
+