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Fix off-by-one UART bitrate counter value that will make the RX sampling

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and TX sending drift. The impact gets higher as the baudrate increases and
the bitrate counter value gets smaller.
This commit is contained in:
Jonas Thörnblad 2024-12-16 13:05:36 +01:00
parent 66888a3756
commit 3389d7ebf3
No known key found for this signature in database
GPG Key ID: 2D318AD00A326F95
2 changed files with 86 additions and 70 deletions
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2
hw/application_fpga/application_fpga.bin.sha256
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@ -1 +1 @@
44086edb70377991b57d3f1c231f743fcf0c2c9d2303843ec133f76cc42449a8 application_fpga.bin
f66159016ebbc98e07d0a1cb01d779d0e898eaba3a718576ca7f894f7fab7b85 application_fpga.bin

126
hw/application_fpga/core/uart/rtl/uart_core.v
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@ -81,10 +81,9 @@ module uart_core (
parameter ERX_SYN = 4;
parameter ETX_IDLE = 0;
parameter ETX_ACK = 1;
parameter ETX_START = 2;
parameter ETX_BITS = 3;
parameter ETX_STOP = 4;
parameter ETX_START = 1;
parameter ETX_BITS = 2;
parameter ETX_STOP = 3;
//----------------------------------------------------------------
@ -171,19 +170,19 @@ module uart_core (
//----------------------------------------------------------------
always @(posedge clk) begin : reg_update
if (!reset_n) begin
rxd0_reg <= 1'b0;
rxd_reg <= 1'b0;
rxd0_reg <= 0;
rxd_reg <= 0;
rxd_byte_reg <= 8'h0;
rxd_bit_ctr_reg <= 4'h0;
rxd_bitrate_ctr_reg <= 16'h0;
rxd_syn_reg <= 0;
erx_ctrl_reg <= ERX_IDLE;
txd_reg <= 1'b1;
txd_reg <= 1;
txd_byte_reg <= 8'h0;
txd_bit_ctr_reg <= 4'h0;
txd_bitrate_ctr_reg <= 16'h0;
txd_ready_reg <= 1'b1;
txd_ready_reg <= 1;
etx_ctrl_reg <= ETX_IDLE;
end
@ -246,16 +245,16 @@ module uart_core (
//----------------------------------------------------------------
always @* begin : rxd_bit_ctr
rxd_bit_ctr_new = 4'h0;
rxd_bit_ctr_we = 1'b0;
rxd_bit_ctr_we = 0;
if (rxd_bit_ctr_rst) begin
rxd_bit_ctr_new = 4'h0;
rxd_bit_ctr_we = 1'b1;
rxd_bit_ctr_we = 1;
end
else if (rxd_bit_ctr_inc) begin
rxd_bit_ctr_new = rxd_bit_ctr_reg + 1'h1;
rxd_bit_ctr_we = 1'b1;
rxd_bit_ctr_we = 1;
end
end // rxd_bit_ctr
@ -267,22 +266,21 @@ module uart_core (
// serial interface.
//----------------------------------------------------------------
always @* begin : rxd_bitrate_ctr
rxd_bitrate_ctr_new = 16'h0;
rxd_bitrate_ctr_we = 1'h0;
rxd_bitrate_ctr_new = 16'h1;
rxd_bitrate_ctr_we = 0;
if (rxd_bitrate_ctr_rst) begin
rxd_bitrate_ctr_new = 16'h0;
rxd_bitrate_ctr_we = 1'b1;
rxd_bitrate_ctr_new = 16'h1;
rxd_bitrate_ctr_we = 1;
end
else if (rxd_bitrate_ctr_inc) begin
rxd_bitrate_ctr_new = rxd_bitrate_ctr_reg + 1'h1;
rxd_bitrate_ctr_we = 1'b1;
rxd_bitrate_ctr_we = 1;
end
end // rxd_bitrate_ctr
//----------------------------------------------------------------
// txd_bit_ctr
//
@ -291,16 +289,16 @@ module uart_core (
//----------------------------------------------------------------
always @* begin : txd_bit_ctr
txd_bit_ctr_new = 4'h0;
txd_bit_ctr_we = 1'h0;
txd_bit_ctr_we = 0;
if (txd_bit_ctr_rst) begin
txd_bit_ctr_new = 4'h0;
txd_bit_ctr_we = 1'h1;
txd_bit_ctr_we = 1;
end
else if (txd_bit_ctr_inc) begin
txd_bit_ctr_new = txd_bit_ctr_reg + 1'h1;
txd_bit_ctr_we = 1'b1;
txd_bit_ctr_we = 1;
end
end // txd_bit_ctr
@ -312,11 +310,11 @@ module uart_core (
// serial interface.
//----------------------------------------------------------------
always @* begin : txd_bitrate_ctr
txd_bitrate_ctr_new = 16'h0;
txd_bitrate_ctr_new = 16'h1;
txd_bitrate_ctr_we = 0;
if (txd_bitrate_ctr_rst) begin
txd_bitrate_ctr_new = 16'h0;
txd_bitrate_ctr_new = 16'h1;
txd_bitrate_ctr_we = 1;
end
@ -350,25 +348,32 @@ module uart_core (
ERX_IDLE: begin
if (!rxd_reg) begin
// Possible start bit detected.
rxd_bitrate_ctr_rst = 1;
rxd_bitrate_ctr_inc = 1;
erx_ctrl_new = ERX_START;
erx_ctrl_we = 1;
end
end
ERX_START: begin
rxd_bitrate_ctr_inc = 1;
if (rxd_reg) begin
// Just a glitch.
rxd_bitrate_ctr_rst = 1;
erx_ctrl_new = ERX_IDLE;
erx_ctrl_we = 1;
end
else begin
if (rxd_bitrate_ctr_reg == half_bit_rate) begin
// start bit assumed. We start sampling data.
rxd_bit_ctr_rst = 1;
if (rxd_bitrate_ctr_reg < half_bit_rate) begin
rxd_bitrate_ctr_inc = 1;
end
else begin
// Start bit assumed.
// We are in the middle of the start bit.
// Start sampling data.
rxd_bitrate_ctr_rst = 1;
rxd_bit_ctr_rst = 1;
erx_ctrl_new = ERX_BITS;
erx_ctrl_we = 1;
end
@ -382,11 +387,14 @@ module uart_core (
end
else begin
rxd_byte_we = 1;
rxd_bit_ctr_inc = 1;
if (rxd_bit_ctr_reg < data_bits) begin
rxd_bitrate_ctr_rst = 1;
if (rxd_bit_ctr_reg == (data_bits - 1)) begin
erx_ctrl_new = ERX_STOP;
rxd_bit_ctr_inc = 1;
rxd_byte_we = 1; // We are in the middle of a data bit, make a sample
end
else begin
erx_ctrl_new = ERX_STOP; // We are now in the middle of the stop bit
erx_ctrl_we = 1;
end
end
@ -394,8 +402,13 @@ module uart_core (
ERX_STOP: begin
// stop_bits can be removed from line below if we are only using one stop bit
if (rxd_bitrate_ctr_reg < (bit_rate * stop_bits)) begin
rxd_bitrate_ctr_inc = 1;
if (rxd_bitrate_ctr_reg == bit_rate * stop_bits) begin
end
else begin
rxd_bitrate_ctr_rst = 1;
rxd_syn_new = 1;
rxd_syn_we = 1;
erx_ctrl_new = ERX_SYN;
@ -444,22 +457,15 @@ module uart_core (
ETX_IDLE: begin
txd_new = 1;
txd_we = 1;
txd_bit_ctr_rst = 1;
if (txd_syn) begin
txd_new = 0;
txd_we = 1;
txd_byte_new = txd_data;
txd_byte_we = 1;
txd_ready_new = 0;
txd_ready_we = 1;
txd_bitrate_ctr_rst = 1;
etx_ctrl_new = ETX_ACK;
etx_ctrl_we = 1;
end
end
ETX_ACK: begin
if (!txd_syn) begin
txd_new = 0;
txd_we = 1;
etx_ctrl_new = ETX_START;
etx_ctrl_we = 1;
end
@ -467,14 +473,17 @@ module uart_core (
ETX_START: begin
if (txd_bitrate_ctr_reg == bit_rate) begin
txd_bit_ctr_rst = 1;
etx_ctrl_new = ETX_BITS;
etx_ctrl_we = 1;
if (txd_bitrate_ctr_reg < bit_rate) begin
txd_bitrate_ctr_inc = 1;
end
else begin
txd_bitrate_ctr_inc = 1;
txd_bitrate_ctr_rst = 1;
txd_bit_ctr_inc = 1;
txd_new = txd_byte_reg[txd_bit_ctr_reg[2 : 0]];
txd_we = 1;
etx_ctrl_new = ETX_BITS;
etx_ctrl_we = 1;
end
end
@ -486,25 +495,32 @@ module uart_core (
else begin
txd_bitrate_ctr_rst = 1;
if (txd_bit_ctr_reg == data_bits) begin
if (txd_bit_ctr_reg < data_bits) begin
txd_bit_ctr_inc = 1;
txd_new = txd_byte_reg[txd_bit_ctr_reg[2 : 0]];
txd_we = 1;
end
else begin
txd_new = 1;
txd_we = 1;
etx_ctrl_new = ETX_STOP;
etx_ctrl_we = 1;
end
else begin
txd_new = txd_byte_reg[txd_bit_ctr_reg[2 : 0]];
txd_we = 1;
txd_bit_ctr_inc = 1;
end
end
end
ETX_STOP: begin
// stop_bits can be removed from line below if we are only using one stop bit
if (txd_bitrate_ctr_reg < (bit_rate * stop_bits)) begin
txd_bitrate_ctr_inc = 1;
if (txd_bitrate_ctr_reg == bit_rate * stop_bits) begin
end
else begin
txd_bitrate_ctr_rst = 1;
txd_bit_ctr_rst = 1;
txd_ready_new = 1;
txd_ready_we = 1;
etx_ctrl_new = ETX_IDLE;