////////////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////
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//
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//
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// Filename: ziptimer.v
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// Filename: ziptimer.v
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//
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//
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// Project: Zip CPU -- a small, lightweight, RISC CPU soft core
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// Project: Zip CPU -- a small, lightweight, RISC CPU soft core
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//
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//
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// Purpose: A lighter weight implementation of the Zip Timer.
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// Purpose: A lighter weight implementation of the Zip Timer.
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//
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//
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// Interface:
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// Interface:
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// Two options:
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// Two options:
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// 1. One combined register for both control and value, and ...
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// 1. One combined register for both control and value, and ...
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// The reload value is set any time the timer data value is "set".
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// The reload value is set any time the timer data value is "set".
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// Reading the register returns the timer value. Controls are
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// Reading the register returns the timer value. Controls are
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// set so that writing a value to the timer automatically starts
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// set so that writing a value to the timer automatically starts
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// it counting down.
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// it counting down.
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// 2. Two registers, one for control one for value.
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// 2. Two registers, one for control one for value.
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// The control register would have the reload value in it.
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// The control register would have the reload value in it.
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// On the clock when the interface is set to zero the interrupt is set.
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// On the clock when the interface is set to zero the interrupt is set.
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// Hence setting the timer to zero will disable the timer without
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// Hence setting the timer to zero will disable the timer without
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// setting any interrupts. Thus setting it to five will count
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// setting any interrupts. Thus setting it to five will count
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// 5 clocks: 5, 4, 3, 2, 1, Interrupt.
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// 5 clocks: 5, 4, 3, 2, 1, Interrupt.
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//
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//
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//
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//
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// Control bits:
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// Control bits:
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// (Start_n/Stop. This bit has been dropped. Writing to this
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// (Start_n/Stop. This bit has been dropped. Writing to this
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// timer any value but zero starts it. Writing a zero
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// timer any value but zero starts it. Writing a zero
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// clears and stops it.)
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// clears and stops it.)
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// AutoReload. If set, then on reset the timer automatically
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// AutoReload. If set, then on reset the timer automatically
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// loads the last set value and starts over. This is
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// loads the last set value and starts over. This is
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// useful for distinguishing between a one-time interrupt
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// useful for distinguishing between a one-time interrupt
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// timer, and a repetitive interval timer.
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// timer, and a repetitive interval timer.
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// (INTEN. Interrupt enable--reaching zero always creates an
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// (INTEN. Interrupt enable--reaching zero always creates an
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// interrupt, so this control bit isn't needed. The
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// interrupt, so this control bit isn't needed. The
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// interrupt controller can be used to mask the interrupt.)
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// interrupt controller can be used to mask the interrupt.)
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// (COUNT-DOWN/UP: This timer is *only* a count-down timer.
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// (COUNT-DOWN/UP: This timer is *only* a count-down timer.
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// There is no means of setting it to count up.)
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// There is no means of setting it to count up.)
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// WatchDog
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// WatchDog
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// This timer can be implemented as a watchdog timer simply by
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// This timer can be implemented as a watchdog timer simply by
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// connecting the interrupt line to the reset line of the CPU.
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// connecting the interrupt line to the reset line of the CPU.
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// When the timer then expires, it will trigger a CPU reset.
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// When the timer then expires, it will trigger a CPU reset.
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//
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//
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//
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//
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// Creator: Dan Gisselquist, Ph.D.
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// Creator: Dan Gisselquist, Ph.D.
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// Gisselquist Technology, LLC
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// Gisselquist Technology, LLC
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//
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//
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////////////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////
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//
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//
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// Copyright (C) 2015,2017, Gisselquist Technology, LLC
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// Copyright (C) 2015,2017-2019, Gisselquist Technology, LLC
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//
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//
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// This program is free software (firmware): you can redistribute it and/or
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// This program is free software (firmware): you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as published
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// modify it under the terms of the GNU General Public License as published
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// by the Free Software Foundation, either version 3 of the License, or (at
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// by the Free Software Foundation, either version 3 of the License, or (at
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// your option) any later version.
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// your option) any later version.
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//
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//
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// This program is distributed in the hope that it will be useful, but WITHOUT
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// This program is distributed in the hope that it will be useful, but WITHOUT
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// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
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// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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// for more details.
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// for more details.
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//
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//
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// You should have received a copy of the GNU General Public License along
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// You should have received a copy of the GNU General Public License along
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// with this program. (It's in the $(ROOT)/doc directory. Run make with no
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// with this program. (It's in the $(ROOT)/doc directory. Run make with no
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// target there if the PDF file isn't present.) If not, see
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// target there if the PDF file isn't present.) If not, see
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// <http://www.gnu.org/licenses/> for a copy.
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// <http://www.gnu.org/licenses/> for a copy.
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//
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//
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// License: GPL, v3, as defined and found on www.gnu.org,
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// License: GPL, v3, as defined and found on www.gnu.org,
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// http://www.gnu.org/licenses/gpl.html
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// http://www.gnu.org/licenses/gpl.html
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//
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//
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//
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//
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////////////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////
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//
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//
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//
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//
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module ziptimer(i_clk, i_rst, i_ce,
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`default_nettype none
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//
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module ziptimer(i_clk, i_reset, i_ce,
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i_wb_cyc, i_wb_stb, i_wb_we, i_wb_data,
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i_wb_cyc, i_wb_stb, i_wb_we, i_wb_data,
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o_wb_ack, o_wb_stall, o_wb_data,
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o_wb_ack, o_wb_stall, o_wb_data,
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o_int);
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o_int);
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parameter BW = 32, VW = (BW-1), RELOADABLE=1;
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parameter BW = 32, VW = (BW-1), RELOADABLE=1;
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input i_clk, i_rst, i_ce;
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input wire i_clk, i_reset, i_ce;
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// Wishbone inputs
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// Wishbone inputs
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input i_wb_cyc, i_wb_stb, i_wb_we;
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input wire i_wb_cyc, i_wb_stb, i_wb_we;
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input [(BW-1):0] i_wb_data;
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input wire [(BW-1):0] i_wb_data;
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// Wishbone outputs
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// Wishbone outputs
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output reg o_wb_ack;
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output reg o_wb_ack;
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output wire o_wb_stall;
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output wire o_wb_stall;
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output wire [(BW-1):0] o_wb_data;
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output wire [(BW-1):0] o_wb_data;
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// Interrupt line
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// Interrupt line
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output reg o_int;
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output reg o_int;
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reg r_running;
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reg r_running;
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wire wb_write;
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wire wb_write;
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assign wb_write = ((i_wb_cyc)&&(i_wb_stb)&&(i_wb_we));
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assign wb_write = ((i_wb_stb)&&(i_wb_we));
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wire auto_reload;
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wire auto_reload;
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wire [(VW-1):0] reload_value;
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wire [(VW-1):0] interval_count;
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initial r_running = 1'b0;
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initial r_running = 1'b0;
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always @(posedge i_clk)
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always @(posedge i_clk)
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if (i_rst)
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if (i_reset)
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r_running <= 1'b0;
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r_running <= 1'b0;
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else if (wb_write)
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else if (wb_write)
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r_running <= (|i_wb_data[(VW-1):0]);
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r_running <= (|i_wb_data[(VW-1):0]);
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else if ((o_int)&&(~auto_reload))
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else if ((r_zero)&&(!auto_reload))
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r_running <= 1'b0;
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r_running <= 1'b0;
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generate
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generate
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if (RELOADABLE != 0)
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if (RELOADABLE != 0)
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begin
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begin
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reg r_auto_reload;
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reg r_auto_reload;
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reg [(VW-1):0] r_reload_value;
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reg [(VW-1):0] r_interval_count;
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initial r_auto_reload = 1'b0;
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initial r_auto_reload = 1'b0;
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always @(posedge i_clk)
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always @(posedge i_clk)
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if (wb_write)
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if (i_reset)
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r_auto_reload <= (i_wb_data[(BW-1)]);
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r_auto_reload <= 1'b0;
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else if (wb_write)
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r_auto_reload <= (i_wb_data[(BW-1)])
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&&(|i_wb_data[(VW-1):0]);
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assign auto_reload = r_auto_reload;
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assign auto_reload = r_auto_reload;
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// If setting auto-reload mode, and the value to other
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// If setting auto-reload mode, and the value to other
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// than zero, set the auto-reload value
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// than zero, set the auto-reload value
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always @(posedge i_clk)
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always @(posedge i_clk)
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if ((wb_write)&&(i_wb_data[(BW-1)])&&(|i_wb_data[(VW-1):0]))
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if (wb_write)
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r_reload_value <= i_wb_data[(VW-1):0];
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r_interval_count <= i_wb_data[(VW-1):0];
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assign reload_value = r_reload_value;
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assign interval_count = r_interval_count;
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end else begin
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end else begin
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assign auto_reload = 1'b0;
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assign auto_reload = 1'b0;
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assign reload_value = 0;
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assign interval_count = 0;
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end endgenerate
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end endgenerate
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reg [(VW-1):0] r_value;
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reg [(VW-1):0] r_value;
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initial r_value = 0;
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initial r_value = 0;
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always @(posedge i_clk)
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always @(posedge i_clk)
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if (wb_write)
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if (i_reset)
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r_value <= 0;
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else if (wb_write)
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r_value <= i_wb_data[(VW-1):0];
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r_value <= i_wb_data[(VW-1):0];
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else if ((r_running)&&(i_ce)&&(~o_int))
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else if ((i_ce)&&(r_running))
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r_value <= r_value + {(VW){1'b1}}; // r_value - 1;
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begin
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else if ((r_running)&&(auto_reload)&&(o_int))
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if (!r_zero)
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r_value <= reload_value;
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r_value <= r_value - 1'b1;
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else if (auto_reload)
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r_value <= interval_count;
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end
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reg r_zero = 1'b1;
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always @(posedge i_clk)
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if (i_reset)
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r_zero <= 1'b1;
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else if (wb_write)
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r_zero <= (i_wb_data[(VW-1):0] == 0);
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else if ((r_running)&&(i_ce))
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begin
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if (r_value == { {(VW-1){1'b0}}, 1'b1 })
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r_zero <= 1'b1;
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else if ((r_zero)&&(auto_reload))
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r_zero <= 1'b0;
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end
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// Set the interrupt on our last tick, as we transition from one to
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// Set the interrupt on our last tick, as we transition from one to
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// zero.
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// zero.
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initial o_int = 1'b0;
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initial o_int = 1'b0;
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always @(posedge i_clk)
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always @(posedge i_clk)
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if (i_rst)
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if ((i_reset)||(wb_write)||(!i_ce))
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o_int <= 1'b0;
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else if (i_ce)
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o_int <= (r_running)&&(r_value == { {(VW-1){1'b0}}, 1'b1 });
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else
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o_int <= 1'b0;
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o_int <= 1'b0;
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else // if (i_ce)
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o_int <= (r_value == { {(VW-1){1'b0}}, 1'b1 });
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initial o_wb_ack = 1'b0;
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initial o_wb_ack = 1'b0;
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always @(posedge i_clk)
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always @(posedge i_clk)
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o_wb_ack <= (i_wb_cyc)&&(i_wb_stb);
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o_wb_ack <= (!i_reset)&&(i_wb_stb);
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assign o_wb_stall = 1'b0;
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assign o_wb_stall = 1'b0;
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generate
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generate
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if (VW < BW-1)
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if (VW < BW-1)
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assign o_wb_data = { auto_reload, {(BW-1-VW){1'b0}}, r_value };
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assign o_wb_data = { auto_reload, {(BW-1-VW){1'b0}}, r_value };
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else
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else
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assign o_wb_data = { auto_reload, r_value };
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assign o_wb_data = { auto_reload, r_value };
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endgenerate
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endgenerate
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// Make verilator happy
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// verilator lint_off UNUSED
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wire [32:0] unused;
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assign unused = { i_wb_cyc, i_wb_data };
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// verilator lint_on UNUSED
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`ifdef FORMAL
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reg f_past_valid;
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initial f_past_valid = 1'b0;
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always @(posedge i_clk)
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f_past_valid <= 1'b1;
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initial assume(i_reset);
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always @(*)
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if (!f_past_valid)
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assume(i_reset);
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always @(posedge i_clk)
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if ((!f_past_valid)||($past(i_reset)))
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begin
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assert(r_value == 0);
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assert(r_running == 0);
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assert(auto_reload == 0);
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assert(r_zero == 1'b1);
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end
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always @(*)
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assert(r_zero == (r_value == 0));
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always @(*)
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if (r_value != 0)
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assert(r_running);
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always @(*)
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if (auto_reload)
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assert(r_running);
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always @(*)
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if (!RELOADABLE)
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assert(auto_reload == 0);
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always @(*)
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if (auto_reload)
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assert(interval_count != 0);
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always @(posedge i_clk)
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if ((f_past_valid)&&($past(r_value)==0)
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&&(!$past(wb_write))&&(!$past(auto_reload)))
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assert(r_value == 0);
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always @(posedge i_clk)
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if ((f_past_valid)&&(!$past(i_reset))&&(!$past(wb_write))
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&&($past(r_value)==0)&&($past(auto_reload)))
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begin
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if ($past(i_ce))
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assert(r_value == interval_count);
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else
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assert(r_value == $past(r_value));
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end
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always @(posedge i_clk)
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if ((f_past_valid)&&(!$past(i_reset))
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&&(!$past(wb_write))&&($past(r_value)!=0))
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begin
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if ($past(i_ce))
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assert(r_value == $past(r_value)-1'b1);
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else
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assert(r_value == $past(r_value));
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end
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always @(posedge i_clk)
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if ((f_past_valid)&&(!$past(i_reset))&&($past(wb_write)))
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assert(r_value == $past(i_wb_data[(VW-1):0]));
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always @(posedge i_clk)
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if ((f_past_valid)&&(!$past(i_reset))&&($past(wb_write))
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&&(RELOADABLE)&&(|$past(i_wb_data[(VW-1):0])))
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assert(auto_reload == $past(i_wb_data[(BW-1)]));
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always @(posedge i_clk)
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if (!(f_past_valid)||($past(i_reset)))
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assert(!o_int);
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else if (($past(wb_write))||(!$past(i_ce)))
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assert(!o_int);
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else
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assert(o_int == ((r_running)&&(r_value == 0)));
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always @(posedge i_clk)
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if ((!f_past_valid)||($past(i_reset)))
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assert(!o_wb_ack);
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else if ($past(i_wb_stb))
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assert(o_wb_ack);
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always @(*)
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assert(!o_wb_stall);
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always @(*)
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assert(o_wb_data[BW-1] == auto_reload);
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always @(*)
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assert(o_wb_data[VW-1:0] == r_value);
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`endif
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endmodule
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endmodule
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