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pluto_hdl_adi/library/axi_fan_control/axi_fan_control.v

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// ***************************************************************************
// ***************************************************************************
// Copyright 2014 - 2019 (c) Analog Devices, Inc. All rights reserved.
//
// In this HDL repository, there are many different and unique modules, consisting
// of various HDL (Verilog or VHDL) components. The individual modules are
// developed independently, and may be accompanied by separate and unique license
// terms.
//
// The user should read each of these license terms, and understand the
// freedoms and responsibilities that he or she has by using this source/core.
//
// This core 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.
//
// Redistribution and use of source or resulting binaries, with or without modification
// of this file, are permitted under one of the following two license terms:
//
// 1. The GNU General Public License version 2 as published by the
// Free Software Foundation, which can be found in the top level directory
// of this repository (LICENSE_GPL2), and also online at:
// <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
//
// OR
//
// 2. An ADI specific BSD license, which can be found in the top level directory
// of this repository (LICENSE_ADIBSD), and also on-line at:
// https://github.com/analogdevicesinc/hdl/blob/master/LICENSE_ADIBSD
// This will allow to generate bit files and not release the source code,
// as long as it attaches to an ADI device.
//
// ***************************************************************************
// ***************************************************************************
`timescale 1ns / 1ps
module axi_fan_control #(
parameter ID = 0,
parameter PWM_FREQUENCY_HZ = 5000,
//temperature thresholds defined to match sysmon reg values
parameter THRESH_PWM_000 = 16'h8f5e, //TEMP_05
parameter THRESH_PWM_025_L = 16'h96f0, //TEMP_20
parameter THRESH_PWM_025_H = 16'ha0ff, //TEMP_40
parameter THRESH_PWM_050_L = 16'hab03, //TEMP_60
parameter THRESH_PWM_050_H = 16'hb00a, //TEMP_70
parameter THRESH_PWM_075_L = 16'hb510, //TEMP_80
parameter THRESH_PWM_075_H = 16'hba17, //TEMP_90
parameter THRESH_PWM_100 = 16'hbc9b) ( //TEMP_95
input tacho,
output reg irq,
output pwm,
//axi interface
input s_axi_aclk,
input s_axi_aresetn,
input s_axi_awvalid,
input [15:0] s_axi_awaddr,
input [ 2:0] s_axi_awprot,
output s_axi_awready,
input s_axi_wvalid,
input [31:0] s_axi_wdata,
input [ 3:0] s_axi_wstrb,
output s_axi_wready,
output s_axi_bvalid,
output [ 1:0] s_axi_bresp,
input s_axi_bready,
input s_axi_arvalid,
input [15:0] s_axi_araddr,
input [ 2:0] s_axi_arprot,
output s_axi_arready,
output s_axi_rvalid,
output [ 1:0] s_axi_rresp,
output [31:0] s_axi_rdata,
input s_axi_rready);
//local parameters
localparam [31:0] CORE_VERSION = {16'h0000, /* MAJOR */
8'h01, /* MINOR */
8'h00}; /* PATCH */ // 0.0.0
localparam [31:0] CORE_MAGIC = 32'h46414E43; // FANC
localparam CLK_FREQUENCY = 100000000;
localparam PWM_PERIOD = CLK_FREQUENCY / PWM_FREQUENCY_HZ;
localparam OVERFLOW_LIM = CLK_FREQUENCY * 5;
localparam AVERAGE_DIV = 128;
//pwm params
localparam PWM_ONTIME_25 = PWM_PERIOD / 4;
localparam PWM_ONTIME_50 = PWM_PERIOD / 2;
localparam PWM_ONTIME_75 = PWM_PERIOD * 3 / 4;
//tacho params
localparam TACHO_TOL_PERCENT = 25;
localparam TACHO_T25 = 3200000; // 32 ms
localparam TACHO_T50 = 1280000; // 12.8 ms
localparam TACHO_T75 = 720000; // 7.2 ms
localparam TACHO_T100 = 640000;
localparam TACHO_T25_TOL = TACHO_T25 * TACHO_TOL_PERCENT / 100;
localparam TACHO_T50_TOL = TACHO_T50 * TACHO_TOL_PERCENT / 100;
localparam TACHO_T75_TOL = TACHO_T75 * TACHO_TOL_PERCENT / 100;
localparam TACHO_T100_TOL = TACHO_T100 * TACHO_TOL_PERCENT / 100;
//state machine states
localparam INIT = 8'h00;
localparam DRP_WAIT_EOC = 8'h01;
localparam DRP_WAIT_DRDY = 8'h02;
localparam DRP_READ_TEMP = 8'h03;
localparam DRP_READ_TEMP_WAIT_DRDY = 8'h04;
localparam GET_TACHO = 8'h05;
localparam EVAL_TEMP = 8'h06;
localparam SET_PWM = 8'h07;
localparam EVAL_TACHO = 8'h08;
reg [31:0] up_scratch = 'd0;
reg [7:0] state = INIT;
reg [7:0] drp_daddr = 'h0;
reg [15:0] drp_di = 'h0;
reg [1:0] drp_den_reg = 'h0;
reg [1:0] drp_dwe_reg = 'h0;
reg [15:0] sysmone_temp = 'h0;
reg temp_increase_alarm = 'h0;
reg tacho_alarm = 'h0;
reg [31:0] up_tacho_val = 'h0;
reg [31:0] up_tacho_tol = 'h0;
reg up_tacho_en = 'h0;
reg [7:0] tacho_avg_cnt = 'h0;
reg [31:0] tacho_avg_sum = 'h0;
reg [31:0] tacho_meas = 'h0;
reg tacho_delayed = 'h0;
reg tacho_meas_new = 'h0;
reg tacho_meas_ack = 'h0;
reg tacho_edge_det = 'h0;
reg [31:0] up_tacho_avg_sum = 'h0;
reg [31:0] counter_reg = 'h0;
reg [31:0] pwm_width = 'h0;
reg [31:0] pwm_width_req = 'h0;
reg counter_overflow = 'h0;
reg pwm_change_done = 1'b1;
reg pulse_gen_load_config = 'h0;
reg tacho_meas_int = 'h0;
reg [31:0] up_pwm_width = 'd0;
reg up_wack = 'd0;
reg [31:0] up_rdata = 'd0;
reg up_rack = 'd0;
reg up_resetn = 1'b1;
reg [3:0] up_irq_mask = 4'b1111;
reg [3:0] up_irq_source = 4'h0;
wire counter_resetn;
wire [15:0] drp_do;
wire drp_drdy;
wire drp_eoc;
wire drp_eos;
wire pwm_change_done_int;
wire pulse_gen_out;
wire up_clk;
wire up_rreq_s;
wire [7:0] up_raddr_s;
wire up_wreq_s;
wire [7:0] up_waddr_s;
wire [31:0] up_wdata_s;
wire [3:0] up_irq_pending;
wire [3:0] up_irq_trigger;
wire [3:0] up_irq_source_clear;
assign up_clk = s_axi_aclk;
assign pwm = ~pulse_gen_out & up_resetn; //reverse polarity because the board is also reversing it
assign pwm_change_done_int = counter_overflow & !pwm_change_done;
//IRQ handling
assign up_irq_pending = ~up_irq_mask & up_irq_source;
assign up_irq_trigger = {tacho_meas_int, temp_increase_alarm, tacho_alarm, pwm_change_done_int};
assign up_irq_source_clear = (up_wreq_s == 1'b1 && up_waddr_s == 8'h11) ? up_wdata_s[3:0] : 4'b0000;
//switching the reset signal for the counter
//counter is used to measure tacho and to provide delay between pwm_ontime changes
assign counter_resetn = (pwm_change_done ) ? (!tacho_edge_det) : ((!pwm_change_done) & (!counter_overflow));
up_axi #(
.AXI_ADDRESS_WIDTH(10))
i_up_axi (
.up_rstn (s_axi_aresetn),
.up_clk (up_clk),
.up_axi_awvalid (s_axi_awvalid),
.up_axi_awaddr (s_axi_awaddr),
.up_axi_awready (s_axi_awready),
.up_axi_wvalid (s_axi_wvalid),
.up_axi_wdata (s_axi_wdata),
.up_axi_wstrb (s_axi_wstrb),
.up_axi_wready (s_axi_wready),
.up_axi_bvalid (s_axi_bvalid),
.up_axi_bresp (s_axi_bresp),
.up_axi_bready (s_axi_bready),
.up_axi_arvalid (s_axi_arvalid),
.up_axi_araddr (s_axi_araddr),
.up_axi_arready (s_axi_arready),
.up_axi_rvalid (s_axi_rvalid),
.up_axi_rresp (s_axi_rresp),
.up_axi_rdata (s_axi_rdata),
.up_axi_rready (s_axi_rready),
.up_wreq (up_wreq_s),
.up_waddr (up_waddr_s),
.up_wdata (up_wdata_s),
.up_wack (up_wack),
.up_rreq (up_rreq_s),
.up_raddr (up_raddr_s),
.up_rdata (up_rdata),
.up_rack (up_rack));
SYSMONE4 #(
.COMMON_N_SOURCE(16'hFFFF),
.INIT_40(16'h1000), // config reg 0
.INIT_41(16'h2F9F), // config reg 1
.INIT_42(16'h1400), // config reg 2
.INIT_43(16'h200F), // config reg 3
.INIT_44(16'h0000), // config reg 4
.INIT_45(16'hE200), // Analog Bus Register
.INIT_46(16'h0000), // Sequencer Channel selection (Vuser0-3)
.INIT_47(16'h0000), // Sequencer Average selection (Vuser0-3)
.INIT_48(16'h0101), // Sequencer channel selection
.INIT_49(16'h0000), // Sequencer channel selection
.INIT_4A(16'h0000), // Sequencer Average selection
.INIT_4B(16'h0000), // Sequencer Average selection
.INIT_4C(16'h0000), // Sequencer Bipolar selection
.INIT_4D(16'h0000), // Sequencer Bipolar selection
.INIT_4E(16'h0000), // Sequencer Acq time selection
.INIT_4F(16'h0000), // Sequencer Acq time selection
.INIT_50(16'hB794), // Temp alarm trigger
.INIT_51(16'h4E81), // Vccint upper alarm limit
.INIT_52(16'hA147), // Vccaux upper alarm limit
.INIT_53(16'hBF13), // Temp alarm OT upper
.INIT_54(16'hAB02), // Temp alarm reset
.INIT_55(16'h4963), // Vccint lower alarm limit
.INIT_56(16'h9555), // Vccaux lower alarm limit
.INIT_57(16'hB00A), // Temp alarm OT reset
.INIT_58(16'h4E81), // VCCBRAM upper alarm limit
.INIT_5C(16'h4963), // VCCBRAM lower alarm limit
.INIT_59(16'h4963), // vccpsintlp upper alarm limit
.INIT_5D(16'h451E), // vccpsintlp lower alarm limit
.INIT_5A(16'h4963), // vccpsintfp upper alarm limit
.INIT_5E(16'h451E), // vccpsintfp lower alarm limit
.INIT_5B(16'h9A74), // vccpsaux upper alarm limit
.INIT_5F(16'h91EB), // vccpsaux lower alarm limit
.INIT_60(16'h4D39), // Vuser0 upper alarm limit
.INIT_61(16'h4DA7), // Vuser1 upper alarm limit
.INIT_62(16'h9A74), // Vuser2 upper alarm limit
.INIT_63(16'h9A74), // Vuser3 upper alarm limit
.INIT_68(16'h4C5E), // Vuser0 lower alarm limit
.INIT_69(16'h4BF2), // Vuser1 lower alarm limit
.INIT_6A(16'h98BF), // Vuser2 lower alarm limit
.INIT_6B(16'h98BF), // Vuser3 lower alarm limit
.INIT_7A(16'h0000), // DUAL0 Register
.INIT_7B(16'h0000), // DUAL1 Register
.INIT_7C(16'h0000), // DUAL2 Register
.INIT_7D(16'h0000), // DUAL3 Register
.SIM_DEVICE("ZYNQ_ULTRASCALE"),
.SIM_MONITOR_FILE("design.txt"))
inst_sysmon (
.DADDR(drp_daddr),
.DCLK(up_clk),
.DEN(drp_den_reg[0]),
.DI(drp_di),
.DWE(drp_dwe_reg[0]),
.RESET(!up_resetn),
.DO(drp_do),
.DRDY(drp_drdy),
.EOC(drp_eoc),
.EOS(drp_eos)
);
//pulse generator instance
util_pulse_gen #(
.PULSE_WIDTH(0),
.PULSE_PERIOD(0))
util_pulse_gen_i(
.clk (up_clk),
.rstn (up_resetn),
.pulse_width (pwm_width),
.pulse_period (PWM_PERIOD),
.load_config (pulse_gen_load_config),
.pulse (pulse_gen_out)
);
//state machine
always @(posedge up_clk)
if (up_resetn == 1'b0) begin
tacho_alarm <= 'h0;
drp_den_reg <= 'h0;
drp_dwe_reg <= 'h0;
drp_di <= 'h0;
tacho_avg_cnt <= 'h0;
tacho_avg_sum <= 'h0;
tacho_meas_ack <= 'h0;
pulse_gen_load_config <= 'h0;
sysmone_temp <= 'h0;
pwm_width_req <= 'h0;
pwm_width <= 'h0;
up_tacho_avg_sum <= 'h0;
temp_increase_alarm <= 'h0;
tacho_meas_int <= 1'b0;
state <= INIT;
end else begin
case (state)
INIT : begin
drp_daddr <= 8'h40;
// performing read
drp_den_reg <= 2'h2;
if (drp_eoc == 1'b1) begin
state <= DRP_WAIT_EOC;
end
end
DRP_WAIT_EOC : begin
if (drp_eoc == 1'b1) begin
//Clearing AVG bits for Configreg0
drp_di <= drp_do & 16'h03FF;
drp_daddr <= 8'h40;
drp_den_reg <= 2'h2;
// performing write
drp_dwe_reg <= 2'h2;
state <= DRP_WAIT_DRDY;
end else begin
drp_den_reg <= {1'b0, drp_den_reg[1]};
drp_dwe_reg <= {1'b0, drp_dwe_reg[1]};
end
end
DRP_WAIT_DRDY : begin
if (drp_drdy == 1'b1) begin
state <= DRP_READ_TEMP;
end else begin
drp_den_reg <= {1'b0, drp_den_reg[1]};
drp_dwe_reg <= {1'b0, drp_dwe_reg[1]};
end
end
DRP_READ_TEMP : begin
tacho_alarm <= 1'b0;
tacho_meas_int <= 1'b0;
pulse_gen_load_config <= 1'b0;
drp_daddr <= 8'h00;
// performing read
drp_den_reg <= 2'h2;
if (drp_eos == 1'b1) begin
state <= DRP_READ_TEMP_WAIT_DRDY;
end
end
DRP_READ_TEMP_WAIT_DRDY : begin
if (drp_drdy == 1'b1) begin
sysmone_temp <= drp_do;
state <= GET_TACHO;
end else begin
drp_den_reg <= {1'b0, drp_den_reg[1]};
drp_dwe_reg <= {1'b0, drp_dwe_reg[1]};
end
end
GET_TACHO : begin
//adding up tacho measurements in order to obtain a mean value from 32 samples
if ((tacho_avg_cnt == AVERAGE_DIV) || (counter_overflow) || (!pwm_change_done)) begin
//once a set measurements has been obtained, reset the values
tacho_avg_sum <= 1'b0;
tacho_avg_cnt <= 1'b0;
tacho_meas_ack <= 1'b0;
end else if ((tacho_meas_new) && (pwm_change_done)) begin
//tacho_meas_new and tacho_meas_ack ensure the value is read at the right time and only once
tacho_avg_sum <= tacho_avg_sum + tacho_meas;
tacho_avg_cnt <= tacho_avg_cnt + 1'b1;
//acknowledge tha the current values has been added
tacho_meas_ack <= 1'b1;
end else begin
tacho_meas_ack <= 1'b0;
end
state <= EVAL_TEMP;
end
EVAL_TEMP : begin
//pwm section
//the pwm only has to be changed when passing through these temperature intervals
if (sysmone_temp < THRESH_PWM_000) begin
//PWM DUTY should be 0%
pwm_width_req <= 1'b0;
end else if ((sysmone_temp > THRESH_PWM_025_L) && (sysmone_temp < THRESH_PWM_025_H)) begin
//PWM DUTY should be 25%
pwm_width_req <= PWM_ONTIME_25;
end else if ((sysmone_temp > THRESH_PWM_050_L) && (sysmone_temp < THRESH_PWM_050_H)) begin
//PWM DUTY should be 50%
pwm_width_req <= PWM_ONTIME_50;
end else if ((sysmone_temp > THRESH_PWM_075_L) && (sysmone_temp < THRESH_PWM_075_H)) begin
//PWM DUTY should be 75%
pwm_width_req <= PWM_ONTIME_75;
end else if (sysmone_temp > THRESH_PWM_100) begin
//PWM DUTY should be 100%
pwm_width_req <= PWM_PERIOD;
//default to 100% duty cycle after reset if not within temperature intervals described above
end else if ((sysmone_temp != 'h0) && (pwm_width == 'h0)) begin
pwm_width_req <= PWM_PERIOD;
end else begin
//if no changes are needed make sure to mantain current pwm
pwm_width_req <= pwm_width;
end
state <= SET_PWM;
end
SET_PWM : begin
if ((up_pwm_width != pwm_width) && (up_pwm_width >= pwm_width_req) && (up_pwm_width <= PWM_PERIOD) && (pwm_change_done)) begin
pwm_width <= up_pwm_width;
pulse_gen_load_config <= 1'b1;
//clear alarm when pwm duty changes
end else if ((pwm_width != pwm_width_req) && (pwm_width_req > up_pwm_width) && (pwm_change_done)) begin
pwm_width <= pwm_width_req;
pulse_gen_load_config <= 1'b1;
temp_increase_alarm <= 1'b1;
//clear alarm when pwm duty changes
end
state <= EVAL_TACHO;
end
EVAL_TACHO : begin
temp_increase_alarm <= 1'b0;
//tacho section
//check if the fan is turning then see if it is turning correctly
if(counter_overflow & pwm_change_done) begin
//if overflow is 1 then the fan is not turning so do something
tacho_alarm <= 1'b1;
end else if (tacho_avg_cnt == AVERAGE_DIV) begin
//check rpm according to the current pwm duty cycle
//tacho_alarm is only asserted for certain known pwm duty cycles and
//for timeout
up_tacho_avg_sum <= tacho_avg_sum [31:7];
tacho_meas_int <= 1'b1;
if ((pwm_width == PWM_ONTIME_25) && (up_tacho_en == 0)) begin
if ((tacho_avg_sum [31:7] > TACHO_T25 + TACHO_T25_TOL) || (tacho_avg_sum [31:7] < TACHO_T25 - TACHO_T25_TOL)) begin
//the fan is turning but not as expected
tacho_alarm <= 1'b1;
end
end else if ((pwm_width == PWM_ONTIME_50) && (up_tacho_en == 0)) begin
if ((tacho_avg_sum [31:7] > TACHO_T50 + TACHO_T50_TOL) || (tacho_avg_sum [31:7] < TACHO_T50 - TACHO_T50_TOL)) begin
//the fan is turning but not as expected
tacho_alarm <= 1'b1;
end
end else if ((pwm_width == PWM_ONTIME_75) && (up_tacho_en == 0)) begin
if ((tacho_avg_sum [31:7] > TACHO_T75 + TACHO_T75_TOL) || (tacho_avg_sum [31:7] < TACHO_T75 - TACHO_T75_TOL)) begin
//the fan is turning but not as expected
tacho_alarm <= 1'b1;
end
end else if ((pwm_width == PWM_PERIOD) && (up_tacho_en == 0)) begin
if ((tacho_avg_sum [31:7] > TACHO_T100 + TACHO_T100_TOL) || (tacho_avg_sum [31:7] < TACHO_T100 - TACHO_T100_TOL)) begin
//the fan is turning but not as expected
tacho_alarm <= 1'b1;
end
end else if ((pwm_width == up_pwm_width) && up_tacho_en) begin
if ((tacho_avg_sum [31:7] > up_tacho_val + up_tacho_tol) || (tacho_avg_sum [31:7] < up_tacho_val - up_tacho_tol)) begin
//the fan is turning but not as expected
tacho_alarm <= 1'b1;
end
end
end
state <= DRP_READ_TEMP;
end
default :
state <= DRP_READ_TEMP;
endcase
end
//axi registers write
always @(posedge up_clk) begin
if (s_axi_aresetn == 1'b0) begin
up_wack <= 'd0;
up_pwm_width <= 'd0;
up_tacho_val <= 'd0;
up_tacho_tol <= 'd0;
up_tacho_en <= 'd0;
up_scratch <= 'd0;
up_irq_mask <= 4'b1111;
up_resetn <= 1'd0;
end else begin
up_wack <= up_wreq_s;
if ((up_wreq_s == 1'b1) && (up_waddr_s == 8'h20)) begin
up_resetn <= up_wdata_s[0];
end
if ((up_wreq_s == 1'b1) && (up_waddr_s == 8'h02)) begin
up_scratch <= up_wdata_s;
end
if ((up_wreq_s == 1'b1) && (up_waddr_s == 8'h21)) begin
up_pwm_width <= up_wdata_s;
up_tacho_en <= 1'b0;
end
if ((up_wreq_s == 1'b1) && (up_waddr_s == 8'h22)) begin
up_tacho_val <= up_wdata_s;
end
if ((up_wreq_s == 1'b1) && (up_waddr_s == 8'h23)) begin
up_tacho_tol <= up_wdata_s;
up_tacho_en <= 1'b1;
end else if (temp_increase_alarm) begin
up_tacho_en <= 1'b0;
end
if ((up_wreq_s == 1'b1) && (up_waddr_s == 8'h10)) begin
up_irq_mask <= up_wdata_s[3:0];
end
end
end
//axi registers read
always @(posedge up_clk) begin
if (s_axi_aresetn == 1'b0) begin
up_rack <= 'd0;
up_rdata <= 'd0;
end else begin
up_rack <= up_rreq_s;
if (up_rreq_s == 1'b1) begin
case (up_raddr_s)
8'h00: up_rdata <= CORE_VERSION;
8'h01: up_rdata <= ID;
8'h02: up_rdata <= up_scratch;
8'h03: up_rdata <= CORE_MAGIC;
8'h20: up_rdata <= up_resetn;
8'h21: up_rdata <= pwm_width;
8'h30: up_rdata <= PWM_PERIOD;
8'h31: up_rdata <= up_tacho_avg_sum;
8'h32: up_rdata <= sysmone_temp;
8'h22: up_rdata <= up_tacho_val;
8'h23: up_rdata <= up_tacho_tol;
8'h10: up_rdata <= up_irq_mask;
8'h11: up_rdata <= up_irq_pending;
8'h12: up_rdata <= up_irq_source;
default: up_rdata <= 0;
endcase
end else begin
up_rdata <= 32'd0;
end
end
end
//IRQ handling
always @(posedge up_clk) begin
if (up_resetn == 1'b0) begin
irq <= 1'b0;
end else begin
irq <= |up_irq_pending;
end
end
always @(posedge up_clk) begin
if (up_resetn == 1'b0) begin
up_irq_source <= 4'b0000;
end else begin
up_irq_source <= up_irq_trigger | (up_irq_source & ~up_irq_source_clear);
end
end
//tacho measurement logic
always @(posedge up_clk) begin
if (up_resetn == 1'b0) begin
tacho_edge_det <= 'h0;
tacho_meas <= 'h0;
tacho_meas_new <= 'h0;
tacho_delayed <= 'h0;
end else begin
//edge detection of tacho signal
tacho_delayed <= tacho;
tacho_edge_det <= tacho & ~tacho_delayed;
if ((tacho_edge_det == 1'b1) && (pwm_change_done)) begin
//measurement is recorded
tacho_meas <= counter_reg;
//signal indicates new measurement completed
tacho_meas_new <= 1'b1;
end else if(tacho_meas_ack == 1'b1) begin
//acknowledge received from state machine
//resetting new measurement flag
tacho_meas_new <= 'h0;
end
end
end
//pwm change proc
always @(posedge up_clk) begin
if (up_resetn == 1'b0) begin
pwm_change_done <= 1'b1;
end else if (counter_overflow) begin
pwm_change_done <= 1'b1;
end else if (pulse_gen_load_config) begin
pwm_change_done <= 'h0;
end
end
//tacho measurement and pwm change delay counter
always @(posedge up_clk) begin
if ((up_resetn & counter_resetn) == 1'b0) begin
counter_reg <= 'h0;
counter_overflow <= 1'b0;
end else begin
if (counter_reg == OVERFLOW_LIM) begin
counter_reg <= 'h0;
counter_overflow <= 1'b1;
end else begin
counter_reg <= counter_reg + 1'b1;
end
end
end
endmodule
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