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microwatt/uart16550/uart_regs.v

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//////////////////////////////////////////////////////////////////////
//// ////
//// uart_regs.v ////
//// ////
//// ////
//// This file is part of the "UART 16550 compatible" project ////
//// http://www.opencores.org/cores/uart16550/ ////
//// ////
//// Documentation related to this project: ////
//// - http://www.opencores.org/cores/uart16550/ ////
//// ////
//// Projects compatibility: ////
//// - WISHBONE ////
//// RS232 Protocol ////
//// 16550D uart (mostly supported) ////
//// ////
//// Overview (main Features): ////
//// Registers of the uart 16550 core ////
//// ////
//// Known problems (limits): ////
//// Inserts 1 wait state in all WISHBONE transfers ////
//// ////
//// To Do: ////
//// Nothing or verification. ////
//// ////
//// Author(s): ////
//// - gorban@opencores.org ////
//// - Jacob Gorban ////
//// - Igor Mohor (igorm@opencores.org) ////
//// ////
//// Created: 2001/05/12 ////
//// Last Updated: (See log for the revision history ////
//// ////
//// ////
//////////////////////////////////////////////////////////////////////
//// ////
//// Copyright (C) 2000, 2001 Authors ////
//// ////
//// This source file may be used and distributed without ////
//// restriction provided that this copyright statement is not ////
//// removed from the file and that any derivative work contains ////
//// the original copyright notice and the associated disclaimer. ////
//// ////
//// This source file is free software; you can redistribute it ////
//// and/or modify it under the terms of the GNU Lesser General ////
//// Public License as published by the Free Software Foundation; ////
//// either version 2.1 of the License, or (at your option) any ////
//// later version. ////
//// ////
//// This source is distributed in the hope that it will be ////
//// useful, but WITHOUT ANY WARRANTY; without even the implied ////
//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ////
//// PURPOSE. See the GNU Lesser General Public License for more ////
//// details. ////
//// ////
//// You should have received a copy of the GNU Lesser General ////
//// Public License along with this source; if not, download it ////
//// from http://www.opencores.org/lgpl.shtml ////
//// ////
//////////////////////////////////////////////////////////////////////
//
// CVS Revision History
//
// $Log: not supported by cvs2svn $
// Revision 1.41 2004/05/21 11:44:41 tadejm
// Added synchronizer flops for RX input.
//
// Revision 1.40 2003/06/11 16:37:47 gorban
// This fixes errors in some cases when data is being read and put to the FIFO at the same time. Patch is submitted by Scott Furman. Update is very recommended.
//
// Revision 1.39 2002/07/29 21:16:18 gorban
// The uart_defines.v file is included again in sources.
//
// Revision 1.38 2002/07/22 23:02:23 gorban
// Bug Fixes:
// * Possible loss of sync and bad reception of stop bit on slow baud rates fixed.
// Problem reported by Kenny.Tung.
// * Bad (or lack of ) loopback handling fixed. Reported by Cherry Withers.
//
// Improvements:
// * Made FIFO's as general inferrable memory where possible.
// So on FPGA they should be inferred as RAM (Distributed RAM on Xilinx).
// This saves about 1/3 of the Slice count and reduces P&R and synthesis times.
//
// * Added optional baudrate output (baud_o).
// This is identical to BAUDOUT* signal on 16550 chip.
// It outputs 16xbit_clock_rate - the divided clock.
// It's disabled by default. Define UART_HAS_BAUDRATE_OUTPUT to use.
//
// Revision 1.37 2001/12/27 13:24:09 mohor
// lsr[7] was not showing overrun errors.
//
// Revision 1.36 2001/12/20 13:25:46 mohor
// rx push changed to be only one cycle wide.
//
// Revision 1.35 2001/12/19 08:03:34 mohor
// Warnings cleared.
//
// Revision 1.34 2001/12/19 07:33:54 mohor
// Synplicity was having troubles with the comment.
//
// Revision 1.33 2001/12/17 10:14:43 mohor
// Things related to msr register changed. After THRE IRQ occurs, and one
// character is written to the transmit fifo, the detection of the THRE bit in the
// LSR is delayed for one character time.
//
// Revision 1.32 2001/12/14 13:19:24 mohor
// MSR register fixed.
//
// Revision 1.31 2001/12/14 10:06:58 mohor
// After reset modem status register MSR should be reset.
//
// Revision 1.30 2001/12/13 10:09:13 mohor
// thre irq should be cleared only when being source of interrupt.
//
// Revision 1.29 2001/12/12 09:05:46 mohor
// LSR status bit 0 was not cleared correctly in case of reseting the FCR (rx fifo).
//
// Revision 1.28 2001/12/10 19:52:41 gorban
// Scratch register added
//
// Revision 1.27 2001/12/06 14:51:04 gorban
// Bug in LSR[0] is fixed.
// All WISHBONE signals are now sampled, so another wait-state is introduced on all transfers.
//
// Revision 1.26 2001/12/03 21:44:29 gorban
// Updated specification documentation.
// Added full 32-bit data bus interface, now as default.
// Address is 5-bit wide in 32-bit data bus mode.
// Added wb_sel_i input to the core. It's used in the 32-bit mode.
// Added debug interface with two 32-bit read-only registers in 32-bit mode.
// Bits 5 and 6 of LSR are now only cleared on TX FIFO write.
// My small test bench is modified to work with 32-bit mode.
//
// Revision 1.25 2001/11/28 19:36:39 gorban
// Fixed: timeout and break didn't pay attention to current data format when counting time
//
// Revision 1.24 2001/11/26 21:38:54 gorban
// Lots of fixes:
// Break condition wasn't handled correctly at all.
// LSR bits could lose their values.
// LSR value after reset was wrong.
// Timing of THRE interrupt signal corrected.
// LSR bit 0 timing corrected.
//
// Revision 1.23 2001/11/12 21:57:29 gorban
// fixed more typo bugs
//
// Revision 1.22 2001/11/12 15:02:28 mohor
// lsr1r error fixed.
//
// Revision 1.21 2001/11/12 14:57:27 mohor
// ti_int_pnd error fixed.
//
// Revision 1.20 2001/11/12 14:50:27 mohor
// ti_int_d error fixed.
//
// Revision 1.19 2001/11/10 12:43:21 gorban
// Logic Synthesis bugs fixed. Some other minor changes
//
// Revision 1.18 2001/11/08 14:54:23 mohor
// Comments in Slovene language deleted, few small fixes for better work of
// old tools. IRQs need to be fix.
//
// Revision 1.17 2001/11/07 17:51:52 gorban
// Heavily rewritten interrupt and LSR subsystems.
// Many bugs hopefully squashed.
//
// Revision 1.16 2001/11/02 09:55:16 mohor
// no message
//
// Revision 1.15 2001/10/31 15:19:22 gorban
// Fixes to break and timeout conditions
//
// Revision 1.14 2001/10/29 17:00:46 gorban
// fixed parity sending and tx_fifo resets over- and underrun
//
// Revision 1.13 2001/10/20 09:58:40 gorban
// Small synopsis fixes
//
// Revision 1.12 2001/10/19 16:21:40 gorban
// Changes data_out to be synchronous again as it should have been.
//
// Revision 1.11 2001/10/18 20:35:45 gorban
// small fix
//
// Revision 1.10 2001/08/24 21:01:12 mohor
// Things connected to parity changed.
// Clock devider changed.
//
// Revision 1.9 2001/08/23 16:05:05 mohor
// Stop bit bug fixed.
// Parity bug fixed.
// WISHBONE read cycle bug fixed,
// OE indicator (Overrun Error) bug fixed.
// PE indicator (Parity Error) bug fixed.
// Register read bug fixed.
//
// Revision 1.10 2001/06/23 11:21:48 gorban
// DL made 16-bit long. Fixed transmission/reception bugs.
//
// Revision 1.9 2001/05/31 20:08:01 gorban
// FIFO changes and other corrections.
//
// Revision 1.8 2001/05/29 20:05:04 gorban
// Fixed some bugs and synthesis problems.
//
// Revision 1.7 2001/05/27 17:37:49 gorban
// Fixed many bugs. Updated spec. Changed FIFO files structure. See CHANGES.txt file.
//
// Revision 1.6 2001/05/21 19:12:02 gorban
// Corrected some Linter messages.
//
// Revision 1.5 2001/05/17 18:34:18 gorban
// First 'stable' release. Should be sythesizable now. Also added new header.
//
// Revision 1.0 2001-05-17 21:27:11+02 jacob
// Initial revision
//
//
`include "uart_defines.v"
`define UART_DL1 7:0
`define UART_DL2 15:8
module uart_regs
#(parameter SIM = 0)
(clk,
wb_rst_i, wb_addr_i, wb_dat_i, wb_dat_o, wb_we_i, wb_re_i,
// additional signals
modem_inputs,
stx_pad_o, srx_pad_i,
rts_pad_o, dtr_pad_o, int_o
`ifdef UART_HAS_BAUDRATE_OUTPUT
, baud_o
`endif
);
input clk;
input wb_rst_i;
input [2:0] wb_addr_i;
input [7:0] wb_dat_i;
output [7:0] wb_dat_o;
input wb_we_i;
input wb_re_i;
output stx_pad_o;
input srx_pad_i;
input [3:0] modem_inputs;
output rts_pad_o;
output dtr_pad_o;
output int_o;
`ifdef UART_HAS_BAUDRATE_OUTPUT
output baud_o;
`endif
wire [3:0] modem_inputs;
reg enable;
`ifdef UART_HAS_BAUDRATE_OUTPUT
assign baud_o = enable; // baud_o is actually the enable signal
`endif
wire stx_pad_o; // received from transmitter module
wire srx_pad_i;
wire srx_pad;
reg [7:0] wb_dat_o;
wire [2:0] wb_addr_i;
wire [7:0] wb_dat_i;
reg [3:0] ier;
reg [3:0] iir;
reg [1:0] fcr; /// bits 7 and 6 of fcr. Other bits are ignored
reg [4:0] mcr;
reg [7:0] lcr;
reg [7:0] msr;
reg [15:0] dl; // 32-bit divisor latch
reg [7:0] scratch; // UART scratch register
reg start_dlc; // activate dlc on writing to UART_DL1
reg lsr_mask_d; // delay for lsr_mask condition
reg msi_reset; // reset MSR 4 lower bits indicator
//reg threi_clear; // THRE interrupt clear flag
reg [15:0] dlc; // 32-bit divisor latch counter
reg int_o;
reg [3:0] trigger_level; // trigger level of the receiver FIFO
reg rx_reset;
reg tx_reset;
wire dlab; // divisor latch access bit
wire cts_pad_i, dsr_pad_i, ri_pad_i, dcd_pad_i; // modem status bits
wire loopback; // loopback bit (MCR bit 4)
wire cts, dsr, ri, dcd; // effective signals
wire cts_c, dsr_c, ri_c, dcd_c; // Complement effective signals (considering loopback)
wire rts_pad_o, dtr_pad_o; // modem control outputs
// LSR bits wires and regs
wire [7:0] lsr;
wire lsr0, lsr1, lsr2, lsr3, lsr4, lsr5, lsr6, lsr7;
reg lsr0r, lsr1r, lsr2r, lsr3r, lsr4r, lsr5r, lsr6r, lsr7r;
wire lsr_mask; // lsr_mask
//
// ASSINGS
//
assign lsr[7:0] = { lsr7r, lsr6r, lsr5r, lsr4r, lsr3r, lsr2r, lsr1r, lsr0r };
assign {cts_pad_i, dsr_pad_i, ri_pad_i, dcd_pad_i} = modem_inputs;
assign {cts, dsr, ri, dcd} = ~{cts_pad_i,dsr_pad_i,ri_pad_i,dcd_pad_i};
assign {cts_c, dsr_c, ri_c, dcd_c} = loopback ? {mcr[`UART_MC_RTS],mcr[`UART_MC_DTR],mcr[`UART_MC_OUT1],mcr[`UART_MC_OUT2]}
: {cts_pad_i,dsr_pad_i,ri_pad_i,dcd_pad_i};
assign dlab = lcr[`UART_LC_DL];
assign loopback = mcr[4];
// assign modem outputs
assign rts_pad_o = mcr[`UART_MC_RTS];
assign dtr_pad_o = mcr[`UART_MC_DTR];
// Interrupt signals
wire rls_int; // receiver line status interrupt
wire rda_int; // receiver data available interrupt
wire ti_int; // timeout indicator interrupt
wire thre_int; // transmitter holding register empty interrupt
wire ms_int; // modem status interrupt
// FIFO signals
reg tf_push;
reg rf_pop;
wire [`UART_FIFO_REC_WIDTH-1:0] rf_data_out;
wire rf_error_bit; // an error (parity or framing) is inside the fifo
wire rf_overrun;
wire rf_push_pulse;
wire [`UART_FIFO_COUNTER_W-1:0] rf_count;
wire [`UART_FIFO_COUNTER_W-1:0] tf_count;
wire [2:0] tstate;
wire [3:0] rstate;
wire [9:0] counter_t;
wire thre_set_en; // THRE status is delayed one character time when a character is written to fifo.
reg [7:0] block_cnt; // While counter counts, THRE status is blocked (delayed one character cycle)
reg [7:0] block_value; // One character length minus stop bit
// Transmitter Instance
wire serial_out;
uart_transmitter #(.SIM (SIM)) transmitter(clk, wb_rst_i, lcr, tf_push, wb_dat_i, enable, serial_out, tstate, tf_count, tx_reset, lsr_mask);
// Synchronizing and sampling serial RX input
uart_sync_flops i_uart_sync_flops
(
.rst_i (wb_rst_i),
.clk_i (clk),
.stage1_rst_i (1'b0),
.stage1_clk_en_i (1'b1),
.async_dat_i (srx_pad_i),
.sync_dat_o (srx_pad)
);
defparam i_uart_sync_flops.width = 1;
defparam i_uart_sync_flops.init_value = 1'b1;
// handle loopback
wire serial_in = loopback ? serial_out : srx_pad;
assign stx_pad_o = loopback ? 1'b1 : serial_out;
// Receiver Instance
uart_receiver receiver(clk, wb_rst_i, lcr, rf_pop, serial_in, enable,
counter_t, rf_count, rf_data_out, rf_error_bit, rf_overrun, rx_reset, lsr_mask, rstate, rf_push_pulse);
// Asynchronous reading here because the outputs are sampled in uart_wb.v file
always @(dl or dlab or ier or iir or scratch
or lcr or lsr or msr or rf_data_out or wb_addr_i or wb_re_i) // asynchrounous reading
begin
case (wb_addr_i)
`UART_REG_RB : wb_dat_o = dlab ? dl[`UART_DL1] : rf_data_out[10:3];
`UART_REG_IE : wb_dat_o = dlab ? dl[`UART_DL2] : {4'd0,ier};
`UART_REG_II : wb_dat_o = {4'b1100,iir};
`UART_REG_LC : wb_dat_o = lcr;
`UART_REG_LS : wb_dat_o = lsr;
`UART_REG_MS : wb_dat_o = msr;
`UART_REG_SR : wb_dat_o = scratch;
default: wb_dat_o = 8'b0; // ??
endcase // case(wb_addr_i)
end // always @ (dl or dlab or ier or iir or scratch...
// rf_pop signal handling
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
rf_pop <= 0;
else
if (rf_pop) // restore the signal to 0 after one clock cycle
rf_pop <= 0;
else
if (wb_re_i && wb_addr_i == `UART_REG_RB && !dlab)
rf_pop <= 1; // advance read pointer
end
wire lsr_mask_condition;
wire iir_read;
wire msr_read;
wire fifo_read;
wire fifo_write;
assign lsr_mask_condition = (wb_re_i && wb_addr_i == `UART_REG_LS && !dlab);
assign iir_read = (wb_re_i && wb_addr_i == `UART_REG_II && !dlab);
assign msr_read = (wb_re_i && wb_addr_i == `UART_REG_MS && !dlab);
assign fifo_read = (wb_re_i && wb_addr_i == `UART_REG_RB && !dlab);
assign fifo_write = (wb_we_i && wb_addr_i == `UART_REG_TR && !dlab);
// lsr_mask_d delayed signal handling
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
lsr_mask_d <= 0;
else // reset bits in the Line Status Register
lsr_mask_d <= lsr_mask_condition;
end
// lsr_mask is rise detected
assign lsr_mask = lsr_mask_condition && ~lsr_mask_d;
// msi_reset signal handling
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
msi_reset <= 1;
else
if (msi_reset)
msi_reset <= 0;
else
if (msr_read)
msi_reset <= 1; // reset bits in Modem Status Register
end
//
// WRITES AND RESETS //
//
// Line Control Register
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i)
lcr <= 8'b00000011; // 8n1 setting
else
if (wb_we_i && wb_addr_i==`UART_REG_LC)
lcr <= wb_dat_i;
// Interrupt Enable Register or UART_DL2
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i)
begin
ier <= 4'b0000; // no interrupts after reset
`ifdef PRESCALER_PRESET_HARD
dl[`UART_DL2] <= `PRESCALER_HIGH_PRESET;
`else
dl[`UART_DL2] <= 8'b0;
`endif
end
else
if (wb_we_i && wb_addr_i==`UART_REG_IE)
if (dlab)
begin
dl[`UART_DL2] <=
`ifdef PRESCALER_PRESET_HARD
dl[`UART_DL2];
`else
wb_dat_i;
`endif
end
else
ier <= wb_dat_i[3:0]; // ier uses only 4 lsb
// FIFO Control Register and rx_reset, tx_reset signals
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) begin
fcr <= 2'b11;
rx_reset <= 0;
tx_reset <= 0;
end else
if (wb_we_i && wb_addr_i==`UART_REG_FC) begin
fcr <= wb_dat_i[7:6];
rx_reset <= wb_dat_i[1];
tx_reset <= wb_dat_i[2];
end else begin
rx_reset <= 0;
tx_reset <= 0;
end
// Modem Control Register
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i)
mcr <= 5'b0;
else
if (wb_we_i && wb_addr_i==`UART_REG_MC)
mcr <= wb_dat_i[4:0];
// Scratch register
// Line Control Register
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i)
scratch <= 0; // 8n1 setting
else
if (wb_we_i && wb_addr_i==`UART_REG_SR)
scratch <= wb_dat_i;
// TX_FIFO or UART_DL1
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i)
begin
`ifdef PRESCALER_PRESET_HARD
dl[`UART_DL1] <= `PRESCALER_LOW_PRESET;
`else
dl[`UART_DL1] <= 8'b0;
`endif
tf_push <= 1'b0;
start_dlc <= 1'b0;
end
else
if (wb_we_i && wb_addr_i==`UART_REG_TR)
if (dlab)
begin
`ifdef PRESCALER_PRESET_HARD
dl[`UART_DL1] <= dl[`UART_DL1];
`else
dl[`UART_DL1] <= wb_dat_i;
`endif
start_dlc <= 1'b1; // enable DL counter
tf_push <= 1'b0;
end
else
begin
tf_push <= 1'b1;
start_dlc <= 1'b0;
end // else: !if(dlab)
else
begin
start_dlc <= 1'b0;
tf_push <= 1'b0;
end // else: !if(dlab)
// Receiver FIFO trigger level selection logic (asynchronous mux)
always @(fcr)
case (fcr[`UART_FC_TL])
2'b00 : trigger_level = 1;
2'b01 : trigger_level = 4;
2'b10 : trigger_level = 8;
2'b11 : trigger_level = 14;
endcase // case(fcr[`UART_FC_TL])
//
// STATUS REGISTERS //
//
// Modem Status Register
reg [3:0] delayed_modem_signals;
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
begin
msr <= 0;
delayed_modem_signals[3:0] <= 0;
end
else begin
msr[`UART_MS_DDCD:`UART_MS_DCTS] <= msi_reset ? 4'b0 :
msr[`UART_MS_DDCD:`UART_MS_DCTS] | ({dcd, ri, dsr, cts} ^ delayed_modem_signals[3:0]);
msr[`UART_MS_CDCD:`UART_MS_CCTS] <= {dcd_c, ri_c, dsr_c, cts_c};
delayed_modem_signals[3:0] <= {dcd, ri, dsr, cts};
end
end
// Line Status Register
// activation conditions
assign lsr0 = (rf_count==0 && rf_push_pulse); // data in receiver fifo available set condition
assign lsr1 = rf_overrun; // Receiver overrun error
assign lsr2 = rf_data_out[1]; // parity error bit
assign lsr3 = rf_data_out[0]; // framing error bit
assign lsr4 = rf_data_out[2]; // break error in the character
assign lsr5 = (tf_count==5'b0 && thre_set_en); // transmitter fifo is empty
assign lsr6 = (tf_count==5'b0 && thre_set_en && (tstate == /*`S_IDLE */ 0)); // transmitter empty
assign lsr7 = rf_error_bit | rf_overrun;
// lsr bit0 (receiver data available)
reg lsr0_d;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr0_d <= 0;
else lsr0_d <= lsr0;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr0r <= 0;
else lsr0r <= (rf_count==1 && rf_pop && !rf_push_pulse || rx_reset) ? 1'b0 : // deassert condition
lsr0r || (lsr0 && ~lsr0_d); // set on rise of lsr0 and keep asserted until deasserted
// lsr bit 1 (receiver overrun)
reg lsr1_d; // delayed
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr1_d <= 0;
else lsr1_d <= lsr1;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr1r <= 0;
else lsr1r <= lsr_mask ? 1'b0 : lsr1r || (lsr1 && ~lsr1_d); // set on rise
// lsr bit 2 (parity error)
reg lsr2_d; // delayed
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr2_d <= 0;
else lsr2_d <= lsr2;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr2r <= 0;
else lsr2r <= lsr_mask ? 1'b0 : lsr2r || (lsr2 && ~lsr2_d); // set on rise
// lsr bit 3 (framing error)
reg lsr3_d; // delayed
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr3_d <= 0;
else lsr3_d <= lsr3;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr3r <= 0;
else lsr3r <= lsr_mask ? 1'b0 : lsr3r || (lsr3 && ~lsr3_d); // set on rise
// lsr bit 4 (break indicator)
reg lsr4_d; // delayed
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr4_d <= 0;
else lsr4_d <= lsr4;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr4r <= 0;
else lsr4r <= lsr_mask ? 1'b0 : lsr4r || (lsr4 && ~lsr4_d);
// lsr bit 5 (transmitter fifo is empty)
reg lsr5_d;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr5_d <= 1;
else lsr5_d <= lsr5;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr5r <= 1;
else lsr5r <= (fifo_write) ? 1'b0 : lsr5r || (lsr5 && ~lsr5_d);
// lsr bit 6 (transmitter empty indicator)
reg lsr6_d;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr6_d <= 1;
else lsr6_d <= lsr6;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr6r <= 1;
else lsr6r <= (fifo_write) ? 1'b0 : lsr6r || (lsr6 && ~lsr6_d);
// lsr bit 7 (error in fifo)
reg lsr7_d;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr7_d <= 0;
else lsr7_d <= lsr7;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) lsr7r <= 0;
else lsr7r <= lsr_mask ? 1'b0 : lsr7r || (lsr7 && ~lsr7_d);
// Frequency divider
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
dlc <= 0;
else
if (start_dlc | ~ (|dlc))
dlc <= dl - 16'd1; // preset counter
else
dlc <= dlc - 16'd1; // decrement counter
end
// Enable signal generation logic
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
enable <= 1'b0;
else
if (|dl & ~(|dlc)) // dl>0 & dlc==0
enable <= 1'b1;
else
enable <= 1'b0;
end
// Delaying THRE status for one character cycle after a character is written to an empty fifo.
always @(lcr)
case (lcr[3:0])
4'b0000 : block_value = 95; // 6 bits
4'b0100 : block_value = 103; // 6.5 bits
4'b0001, 4'b1000 : block_value = 111; // 7 bits
4'b1100 : block_value = 119; // 7.5 bits
4'b0010, 4'b0101, 4'b1001 : block_value = 127; // 8 bits
4'b0011, 4'b0110, 4'b1010, 4'b1101 : block_value = 143; // 9 bits
4'b0111, 4'b1011, 4'b1110 : block_value = 159; // 10 bits
4'b1111 : block_value = 175; // 11 bits
endcase // case(lcr[3:0])
// Counting time of one character minus stop bit
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
block_cnt <= 8'd0;
else
if(lsr5r & fifo_write) // THRE bit set & write to fifo occured
block_cnt <= SIM ? 8'd1 : block_value;
else
if (enable & block_cnt != 8'b0) // only work on enable times
block_cnt <= block_cnt - 8'd1; // decrement break counter
end // always of break condition detection
// Generating THRE status enable signal
assign thre_set_en = ~(|block_cnt);
//
// INTERRUPT LOGIC
//
assign rls_int = ier[`UART_IE_RLS] && (lsr[`UART_LS_OE] || lsr[`UART_LS_PE] || lsr[`UART_LS_FE] || lsr[`UART_LS_BI]);
assign rda_int = ier[`UART_IE_RDA] && (rf_count >= {1'b0,trigger_level});
assign thre_int = ier[`UART_IE_THRE] && lsr[`UART_LS_TFE];
assign ms_int = ier[`UART_IE_MS] && (| msr[3:0]);
assign ti_int = ier[`UART_IE_RDA] && (counter_t == 10'b0) && (|rf_count);
reg rls_int_d;
reg thre_int_d;
reg ms_int_d;
reg ti_int_d;
reg rda_int_d;
// delay lines
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) rls_int_d <= 0;
else rls_int_d <= rls_int;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) rda_int_d <= 0;
else rda_int_d <= rda_int;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) thre_int_d <= 0;
else thre_int_d <= thre_int;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) ms_int_d <= 0;
else ms_int_d <= ms_int;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) ti_int_d <= 0;
else ti_int_d <= ti_int;
// rise detection signals
wire rls_int_rise;
wire thre_int_rise;
wire ms_int_rise;
wire ti_int_rise;
wire rda_int_rise;
assign rda_int_rise = rda_int & ~rda_int_d;
assign rls_int_rise = rls_int & ~rls_int_d;
assign thre_int_rise = thre_int & ~thre_int_d;
assign ms_int_rise = ms_int & ~ms_int_d;
assign ti_int_rise = ti_int & ~ti_int_d;
// interrupt pending flags
reg rls_int_pnd;
reg rda_int_pnd;
reg thre_int_pnd;
reg ms_int_pnd;
reg ti_int_pnd;
// interrupt pending flags assignments
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) rls_int_pnd <= 0;
else
rls_int_pnd <= lsr_mask ? 1'b0 : // reset condition
rls_int_rise ? 1'b1 : // latch condition
rls_int_pnd && ier[`UART_IE_RLS]; // default operation: remove if masked
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) rda_int_pnd <= 0;
else
rda_int_pnd <= ((rf_count == {1'b0,trigger_level}) && fifo_read) ? 1'b0 : // reset condition
rda_int_rise ? 1'b1 : // latch condition
rda_int_pnd && ier[`UART_IE_RDA]; // default operation: remove if masked
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) thre_int_pnd <= 0;
else
thre_int_pnd <= fifo_write || (iir_read & ~iir[`UART_II_IP] & iir[`UART_II_II] == `UART_II_THRE)? 1'b0 :
thre_int_rise ? 1'b1 :
thre_int_pnd && ier[`UART_IE_THRE];
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) ms_int_pnd <= 0;
else
ms_int_pnd <= msr_read ? 1'b0 :
ms_int_rise ? 1'b1 :
ms_int_pnd && ier[`UART_IE_MS];
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) ti_int_pnd <= 0;
else
ti_int_pnd <= fifo_read ? 1'b0 :
ti_int_rise ? 1'b1 :
ti_int_pnd && ier[`UART_IE_RDA];
// end of pending flags
// INT_O logic
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
int_o <= 1'b0;
else
int_o <=
rls_int_pnd ? ~lsr_mask :
rda_int_pnd ? 1'b1 :
ti_int_pnd ? ~fifo_read :
thre_int_pnd ? !(fifo_write & iir_read) :
ms_int_pnd ? ~msr_read :
1'd0; // if no interrupt are pending
end
// Interrupt Identification register
always @(posedge clk or posedge wb_rst_i)
begin
if (wb_rst_i)
iir <= 1;
else
if (rls_int_pnd) // interrupt is pending
begin
iir[`UART_II_II] <= `UART_II_RLS; // set identification register to correct value
iir[`UART_II_IP] <= 1'b0; // and clear the IIR bit 0 (interrupt pending)
end else // the sequence of conditions determines priority of interrupt identification
if (rda_int)
begin
iir[`UART_II_II] <= `UART_II_RDA;
iir[`UART_II_IP] <= 1'b0;
end
else if (ti_int_pnd)
begin
iir[`UART_II_II] <= `UART_II_TI;
iir[`UART_II_IP] <= 1'b0;
end
else if (thre_int_pnd)
begin
iir[`UART_II_II] <= `UART_II_THRE;
iir[`UART_II_IP] <= 1'b0;
end
else if (ms_int_pnd)
begin
iir[`UART_II_II] <= `UART_II_MS;
iir[`UART_II_IP] <= 1'b0;
end else // no interrupt is pending
begin
iir[`UART_II_II] <= 0;
iir[`UART_II_IP] <= 1'b1;
end
end
endmodule
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