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//--------------------------------------------------------------------------------------------------------
// Module : uart_tx
// Type : synthesizable, IP's top
// Standard: Verilog 2001 (IEEE1364-2001)
// Function: input AXI-stream (configurable data width),
// output UART signal
//--------------------------------------------------------------------------------------------------------
module uart_tx #(
// clock frequency
parameter CLK_FREQ = 50000000, // clk frequency, Unit : Hz
// UART format
parameter BAUD_RATE = 115200, // Unit : Hz
parameter PARITY = "NONE", // "NONE", "ODD", or "EVEN"
parameter STOP_BITS = 2, // can be 1, 2, 3, 4, ...
// AXI stream data width
parameter BYTE_WIDTH = 1, // can be 1, 2, 3, 4, ...
// TX fifo depth
parameter FIFO_EA = 0, // 0:no fifo 1,2:depth=4 3:depth=8 4:depth=16 ... 10:depth=1024 11:depth=2048 ...
// do you want to send extra byte after each AXI-stream transfer or packet?
parameter EXTRA_BYTE_AFTER_TRANSFER = "", // specify a extra byte to send after each AXI-stream transfer. when ="", do not send this extra byte
parameter EXTRA_BYTE_AFTER_PACKET = "" // specify a extra byte to send after each AXI-stream packet . when ="", do not send this extra byte
) (
input wire rstn,
input wire clk,
// input stream : AXI-stream slave. Associated clock = clk
output wire i_tready,
input wire i_tvalid,
input wire [8*BYTE_WIDTH-1:0] i_tdata,
input wire [ BYTE_WIDTH-1:0] i_tkeep,
input wire i_tlast,
// UART TX output signal
output reg o_uart_tx
);
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
// TX fifo
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
wire f_tready;
reg f_tvalid;
reg [8*BYTE_WIDTH-1:0] f_tdata;
reg [ BYTE_WIDTH-1:0] f_tkeep;
reg f_tlast;
generate if (FIFO_EA <= 0) begin // no TX fifo
assign i_tready = f_tready;
always @ (*) f_tvalid = i_tvalid;
always @ (*) f_tdata = i_tdata;
always @ (*) f_tkeep = i_tkeep;
always @ (*) f_tlast = i_tlast;
end else begin // TX fifo
localparam EA = (FIFO_EA<=2) ? 2 : FIFO_EA;
localparam DW = ( 1 + BYTE_WIDTH + 8*BYTE_WIDTH ); // 1-bit tlast, (BYTE_WIDTH)-bit tkeep, (8*BYTE_WIDTH)-bit tdata
reg [DW-1:0] buffer [ ((1<<EA)-1) : 0 ];
localparam [EA:0] A_ZERO = {{EA{1'b0}}, 1'b0};
localparam [EA:0] A_ONE = {{EA{1'b0}}, 1'b1};
reg [EA:0] wptr = A_ZERO;
reg [EA:0] wptr_d1 = A_ZERO;
reg [EA:0] wptr_d2 = A_ZERO;
reg [EA:0] rptr = A_ZERO;
wire [EA:0] rptr_next = (f_tvalid & f_tready) ? (rptr+A_ONE) : rptr;
assign i_tready = ( wptr != {~rptr[EA], rptr[EA-1:0]} );
always @ (posedge clk or negedge rstn)
if (~rstn) begin
wptr <= A_ZERO;
wptr_d1 <= A_ZERO;
wptr_d2 <= A_ZERO;
end else begin
if (i_tvalid & i_tready)
wptr <= wptr + A_ONE;
wptr_d1 <= wptr;
wptr_d2 <= wptr_d1;
end
always @ (posedge clk)
if (i_tvalid & i_tready)
buffer[wptr[EA-1:0]] <= {i_tlast, i_tkeep, i_tdata};
always @ (posedge clk or negedge rstn)
if (~rstn) begin
rptr <= A_ZERO;
f_tvalid <= 1'b0;
end else begin
rptr <= rptr_next;
f_tvalid <= (rptr_next != wptr_d2);
end
always @ (posedge clk)
{f_tlast, f_tkeep, f_tdata} <= buffer[rptr_next[EA-1:0]];
initial {f_tvalid, f_tlast, f_tkeep, f_tdata} = 0;
end endgenerate
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
// Generate fractional precise upper limit for counter
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
localparam BAUD_CYCLES = ( (CLK_FREQ*10*2 + BAUD_RATE) / (BAUD_RATE*2) ) / 10 ;
localparam BAUD_CYCLES_FRAC = ( (CLK_FREQ*10*2 + BAUD_RATE) / (BAUD_RATE*2) ) % 10 ;
localparam STOP_BIT_CYCLES = (BAUD_CYCLES_FRAC == 0) ? BAUD_CYCLES : (BAUD_CYCLES + 1);
localparam [9:0] ADDITION_CYCLES = (BAUD_CYCLES_FRAC == 0) ? 10'b0000000000 :
(BAUD_CYCLES_FRAC == 1) ? 10'b0000010000 :
(BAUD_CYCLES_FRAC == 2) ? 10'b0010000100 :
(BAUD_CYCLES_FRAC == 3) ? 10'b0010010010 :
(BAUD_CYCLES_FRAC == 4) ? 10'b0101001010 :
(BAUD_CYCLES_FRAC == 5) ? 10'b0101010101 :
(BAUD_CYCLES_FRAC == 6) ? 10'b1010110101 :
(BAUD_CYCLES_FRAC == 7) ? 10'b1101101101 :
(BAUD_CYCLES_FRAC == 8) ? 10'b1101111011 :
/*BAUD_CYCLES_FRAC == 9)*/ 10'b1111101111 ;
wire [31:0] cycles [9:0];
assign cycles[0] = BAUD_CYCLES + (ADDITION_CYCLES[0] ? 1 : 0);
assign cycles[1] = BAUD_CYCLES + (ADDITION_CYCLES[1] ? 1 : 0);
assign cycles[2] = BAUD_CYCLES + (ADDITION_CYCLES[2] ? 1 : 0);
assign cycles[3] = BAUD_CYCLES + (ADDITION_CYCLES[3] ? 1 : 0);
assign cycles[4] = BAUD_CYCLES + (ADDITION_CYCLES[4] ? 1 : 0);
assign cycles[5] = BAUD_CYCLES + (ADDITION_CYCLES[5] ? 1 : 0);
assign cycles[6] = BAUD_CYCLES + (ADDITION_CYCLES[6] ? 1 : 0);
assign cycles[7] = BAUD_CYCLES + (ADDITION_CYCLES[7] ? 1 : 0);
assign cycles[8] = BAUD_CYCLES + (ADDITION_CYCLES[8] ? 1 : 0);
assign cycles[9] = BAUD_CYCLES + (ADDITION_CYCLES[9] ? 1 : 0);
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
//
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
localparam [BYTE_WIDTH-1:0] ZERO_KEEP = 0;
localparam [31:0] PARITY_BITS = (PARITY == "ODD" || PARITY == "EVEN") ? 1 : 0;
localparam [31:0] TOTAL_BITS = (STOP_BITS >= ('hFFFFFFFF-9-PARITY_BITS)) ? 'hFFFFFFFF : (PARITY_BITS+STOP_BITS+9);
localparam [ 0:0] BYTE_T_EN = (EXTRA_BYTE_AFTER_TRANSFER == "") ? 1'b0 : 1'b1;
localparam [ 0:0] BYTE_B_EN = (EXTRA_BYTE_AFTER_PACKET == "") ? 1'b0 : 1'b1;
localparam [ 7:0] BYTE_T = EXTRA_BYTE_AFTER_TRANSFER;
localparam [ 7:0] BYTE_P = EXTRA_BYTE_AFTER_PACKET;
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
// function for calculate parity bit
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
function [0:0] get_parity;
input [7:0] data;
begin
get_parity = (PARITY == "ODD" ) ? (~(^(data[7:0]))) :
(PARITY == "EVEN") ? (^(data[7:0])) :
/*(PARITY == "NONE")*/ 1'b1 ;
end
endfunction
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
// main FSM
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
localparam [ 1:0] S_IDLE = 2'b01 , // only in state S_IDLE, state[0]==1, the goal is to make f_tready pure register-out
S_PREPARE = 2'b00 ,
S_TX = 2'b10 ;
reg [ 1:0] state = S_IDLE; // FSM state register
reg [8*BYTE_WIDTH-1:0] data = 0;
reg [ BYTE_WIDTH-1:0] keep = 0;
reg byte_t_en = 1'b0;
reg byte_p_en = 1'b0;
reg [ 9:0] txbits = 10'b0;
reg [ 31:0] txcnt = 0;
reg [ 31:0] cycle = 1;
always @ (posedge clk or negedge rstn)
if (~rstn) begin
state <= S_IDLE;
data <= 0;
keep <= 0;
byte_t_en <= 1'b0;
byte_p_en <= 1'b0;
txbits <= 10'b0;
txcnt <= 0;
cycle <= 1;
end else begin
case (state)
S_IDLE : begin
state <= f_tvalid ? S_PREPARE : S_IDLE;
data <= f_tdata;
keep <= f_tkeep;
byte_t_en <= BYTE_T_EN;
byte_p_en <= BYTE_B_EN & f_tlast;
txbits <= 10'b0;
txcnt <= 0;
cycle <= 1;
end
S_PREPARE : begin
data <= (data >> 8);
keep <= (keep >> 1);
if ( keep[0] == 1'b1 ) begin
txbits <= {get_parity(data[7:0]), data[7:0], 1'b0};
state <= S_TX;
end else if ( keep != ZERO_KEEP ) begin
state <= S_PREPARE;
end else if ( byte_t_en ) begin
byte_t_en <= 1'b0;
txbits <= {get_parity(BYTE_T), BYTE_T, 1'b0};
state <= S_TX;
end else if ( byte_p_en ) begin
byte_p_en <= 1'b0;
txbits <= {get_parity(BYTE_P), BYTE_P, 1'b0};
state <= S_TX;
end else begin
state <= S_IDLE;
end
txcnt <= 0;
cycle <= 1;
end
default : begin // S_TX
if (keep[0] == 1'b0) begin
data <= (data >> 8);
keep <= (keep >> 1);
end
if ( cycle < ((txcnt<=9) ? cycles[txcnt] : STOP_BIT_CYCLES) ) begin // cycle loop from 1 to ((txcnt<=9) ? cycles[txcnt] : STOP_BIT_CYCLES)
cycle <= cycle + 1;
end else begin
cycle <= 1;
txbits <= {1'b1, txbits[9:1]}; // right shift txbits, and fill '1' to MSB
if ( txcnt < (TOTAL_BITS-1) ) begin // txcnt loop from 0 to (TOTAL_BITS-1)
txcnt <= txcnt + 1;
end else begin
txcnt <= 0;
state <= S_PREPARE;
end
end
end
endcase
end
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
// generate UART output
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
initial o_uart_tx = 1'b1;
always @ (posedge clk or negedge rstn)
if (~rstn)
o_uart_tx <= 1'b1;
else
o_uart_tx <= (state == S_TX) ? txbits[0] : 1'b1;
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
// generate AXI-stream TREADY
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
assign f_tready = state[0]; // (state == S_IDLE)
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
// parameter checking
//---------------------------------------------------------------------------------------------------------------------------------------------------------------
initial begin
if (BYTE_WIDTH <= 0) begin $error("invalid parameter : BYTE_WIDTH<=0"); $stop; end
if (STOP_BITS <= 0) begin $error("invalid parameter : STOP_BITS <=0"); $stop; end
if (BAUD_CYCLES < 1) begin $error("invalid parameter : BAUD_CYCLES < 1, please use a faster driving clock"); $stop; end
$display("uart_tx : parity = %s" , PARITY );
$display("uart_tx : clock period = %.0f ns (%-10d Hz)" , 1000000000.0/CLK_FREQ , CLK_FREQ );
$display("uart_tx : baud rate period = %.0f ns (%-10d Hz)" , 1000000000.0/BAUD_RATE , BAUD_RATE);
$display("uart_tx : baud cycles = %-10d" , BAUD_CYCLES );
$display("uart_tx : baud cycles frac = %-10d" , BAUD_CYCLES_FRAC );
if (PARITY == "ODD" || PARITY == "EVEN") begin
$display("uart_tx : __ ____ ____ ____ ____ ____ ____ ____ ____________ ");
$display("uart_tx : wave \\____/____X____X____X____X____X____X____X____X____/ ");
$display("uart_tx : bits | S | B0 | B1 | B2 | B3 | B4 | B5 | B6 | B7 | P | ");
$display("uart_tx : time_points t0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 ");
$display("uart_tx :");
end else begin
$display("uart_tx : __ ____ ____ ____ ____ ____ ____ ____ _______ ");
$display("uart_tx : wave \\____/____X____X____X____X____X____X____X____/ ");
$display("uart_tx : bits | S | B0 | B1 | B2 | B3 | B4 | B5 | B6 | B7 | ");
$display("uart_tx : time_points t0 t1 t2 t3 t4 t5 t6 t7 t8 t9 ");
$display("uart_tx :");
end
end
generate genvar index, i;
for (index=0; index<=9; index=index+1) begin : print_and_check_time
localparam cycles_acc = ( (index >= 0) ? (BAUD_CYCLES + (ADDITION_CYCLES[0] ? 1 : 0)) : 0 )
+ ( (index >= 1) ? (BAUD_CYCLES + (ADDITION_CYCLES[1] ? 1 : 0)) : 0 )
+ ( (index >= 2) ? (BAUD_CYCLES + (ADDITION_CYCLES[2] ? 1 : 0)) : 0 )
+ ( (index >= 3) ? (BAUD_CYCLES + (ADDITION_CYCLES[3] ? 1 : 0)) : 0 )
+ ( (index >= 4) ? (BAUD_CYCLES + (ADDITION_CYCLES[4] ? 1 : 0)) : 0 )
+ ( (index >= 5) ? (BAUD_CYCLES + (ADDITION_CYCLES[5] ? 1 : 0)) : 0 )
+ ( (index >= 6) ? (BAUD_CYCLES + (ADDITION_CYCLES[6] ? 1 : 0)) : 0 )
+ ( (index >= 7) ? (BAUD_CYCLES + (ADDITION_CYCLES[7] ? 1 : 0)) : 0 )
+ ( (index >= 8) ? (BAUD_CYCLES + (ADDITION_CYCLES[8] ? 1 : 0)) : 0 )
+ ( (index >= 9) ? (BAUD_CYCLES + (ADDITION_CYCLES[9] ? 1 : 0)) : 0 ) ;
localparam real ideal_time_ns = ((index+1)*1000000000.0/BAUD_RATE);
localparam real actual_time_ns = (cycles_acc*1000000000.0/CLK_FREQ);
localparam real error = (ideal_time_ns>actual_time_ns) ? (ideal_time_ns-actual_time_ns) : (-ideal_time_ns+actual_time_ns);
localparam real relative_error_percent = (error / (1000000000.0/BAUD_RATE)) * 100.0;
initial if (PARITY == "ODD" || PARITY == "EVEN" || index < 9) begin
$display("uart_tx : t%-2d- t0 = %.0f ns (ideal) %.0f ns (actual). error=%.0f ns relative_error=%.3f%%" ,
(index+1) ,
ideal_time_ns ,
actual_time_ns,
error,
relative_error_percent
);
if ( relative_error_percent > 3.0 ) begin $error("relative_error is too large"); $stop; end // if relative error larger than 3%
end
end
endgenerate
endmodule
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