Table of Contents
- Introduction
- Getting Started
- Build and Wiring
- Programming with Vivado Design Suite
- Adding the PIR Motion Sensor
- Experimenting with Automatic Sliding Door
- Summary
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Once we've wired the mini elevator circuit, it's time to program the Arty S7 board.
Finite State Machine
In this project, our timer moves between several different modes, for example: setting the time, then counting down. To handle these different modes, we use a Finite State Machine (FSM).
Finite state machines are one of the most widely used concepts in digital design. A finite state machine has a limited number of states with well-defined transitions between them. Simple real-world FSMs include elevators, traffic lights, and vending machines. For my timer design, I’ve drawn this:
States
- Idle - wait for the user to tell us what to do
- Init - set initial values, such move up or down the elevator.
- Set Time - set time delay of the stepper motor
- Countdown - timer is running
- Done - the elevator is moving up or moving down until the user activates the stop switch
Transitions
- From Idle to Init - user presses control buttons: sw0 (move up or move down the elevator), and sw1 (activate the elevator or stoping it)
- From Init to Set Time - automatically happens after one clock tick
- From Set Time to Countdown - user presses control button
- From Countdown to Done - after the timer reaches zero
- From Done to Idle - after elevator is stoping
FSM Implementation
Now we have a design; we need to translate this into Verilog.
I use what I learned in chapter 3 of this project as a reference, so I have created mini_elevator_arty project as shown below:
Now, I have created Arty-S7-50-Master.xdc constraints file as shown below:
Finally, I have created the file main.sv as shown in the image below:
We declare the input and output ports of the Arty S7 board as follows: a) the LEDs are used to verify if the elevator is active or not, b) the io0, io1, io2, and io3 ports take control of the stepper motor, c) the "sw" switch activates the up or down movement of the elevator, and d) the "en" button activates or stops the elevator.
module main (
input wire logic clk,
input wire logic sw,
input wire logic en,
output logic [3:0] led,
output logic io0,
output logic io1,
output logic io2,
output logic io3
);
A register to track the elevator:
logic light_set; // active elevator: 0 = move down, 1 = move up
For this FSM of the elevator, I’m going to use a single process combining state change and behaviour:
// finite state machine: state change & behavior
enum {IDLE, INIT, FIRST_STEP, SECOND_STEP, THIRD_STEP, FOURTH_STEP, STOP} state;
always_ff @(posedge clk) begin
light_set = sw;
case (state)
IDLE: state <= INIT;
INIT: begin
state <= FIRST_STEP;
light_set <= ~light_set; // switch active light set
end
FIRST_STEP: begin
if (cnt_phase == 0) begin
state <= SECOND_STEP;
cnt_phase <= DELAY;
end else if (stb) cnt_phase <= cnt_phase - 1;
end
SECOND_STEP: begin
if (cnt_phase == 0) begin
state <= THIRD_STEP;
cnt_phase <= DELAY;
end else if (stb) cnt_phase <= cnt_phase - 1;
end
THIRD_STEP: begin
if (cnt_phase == 0) begin
state <= FOURTH_STEP;
cnt_phase <= DELAY;
end else if (stb) cnt_phase <= cnt_phase - 1;
end
FOURTH_STEP: begin
if (cnt_phase == 0) begin
state <= STOP;
cnt_phase <= DELAY;
light_set <= ~light_set; // switch active light set
end else if (stb) cnt_phase <= cnt_phase - 1;
end
STOP: begin
if (en == 1'b1)
state <= FIRST_STEP;
else
state <= STOP;
end
default: state <= STOP;
endcase
end
We control the LEDS and PORTS like so:
// set LEDS based on active light set and state
always_ff @(posedge clk) begin
case (state)
FIRST_STEP: begin
if (light_set == 0) begin
led[0] = 1;
led[1] = 0;
led[2] = 0;
led[3] = 1;
io0 = 1;
io1 = 0;
io2 = 0;
io3 = 1;
end else if (light_set == 1) begin
led[0] = 0;
led[1] = 1;
led[2] = 0;
led[3] = 1;
io0 = 0;
io1 = 1;
io2 = 0;
io3 = 1;
end
end
SECOND_STEP: begin
if (light_set == 0) begin
led[0] = 1;
led[1] = 0;
led[2] = 1;
led[3] = 0;
io0 = 1;
io1 = 0;
io2 = 1;
io3 = 0;
end else if (light_set == 1) begin
led[0] = 0;
led[1] = 1;
led[2] = 1;
led[3] = 0;
io0 = 0;
io1 = 1;
io2 = 1;
io3 = 0;
end
end
THIRD_STEP: begin
if (light_set == 0) begin
led[0] = 0;
led[1] = 1;
led[2] = 1;
led[3] = 0;
io0 = 0;
io1 = 1;
io2 = 1;
io3 = 0;
end else if (light_set == 1) begin
led[0] = 1;
led[1] = 0;
led[2] = 1;
led[3] = 0;
io0 = 1;
io1 = 0;
io2 = 1;
io3 = 0;
end
end
FOURTH_STEP: begin
if (light_set == 0) begin
led[0] = 0;
led[1] = 1;
led[2] = 0;
led[3] = 1;
io0 = 0;
io1 = 1;
io2 = 0;
io3 = 1;
end else if (light_set == 1) begin
led[0] = 1;
led[1] = 0;
led[2] = 0;
led[3] = 1;
io0 = 1;
io1 = 0;
io2 = 0;
io3 = 1;
end
end
STOP: begin
if (light_set == 0) begin
led[0] = 0;
led[1] = 0;
led[2] = 0;
led[3] = 0;
io0 = 0;
io1 = 0;
io2 = 0;
io3 = 0;
end else if (light_set == 1) begin
led[0] = 0;
led[1] = 0;
led[2] = 0;
led[3] = 0;
io0 = 0;
io1 = 0;
io2 = 0;
io3 = 0;
end
end
endcase
end
I have programmed a 20 ms delay in the stepper motor by using a strobe light. My finished main.sv file looks like this
`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// AUTHOR:GUILLERMO PEREZ GUILLEN
//////////////////////////////////////////////////////////////////////////////////
module main (
input wire logic clk,
input wire logic sw,
input wire logic en,
output logic [3:0] led,
output logic io0,
output logic io1,
output logic io2,
output logic io3
);
// stepper motor phases
localparam DELAY = 1;
logic [3:0] cnt_phase; // 4-bit allows up to 15 second phase
logic light_set; // active elevator: 0 = move down, 1 = move up
// generate 20 milliseconds strobe
localparam DIV_BY = 27'd500_000; // 500000 -> 0.020 sec
logic stb;
logic [$clog2(DIV_BY)-1:0] cnt_stb;
always_ff @(posedge clk) begin
if (cnt_stb != DIV_BY-1) begin
stb <= 0;
cnt_stb <= cnt_stb + 1;
end else begin
stb <= 1;
cnt_stb <= 0;
end
end
// finite state machine: state change & behavior
enum {IDLE, INIT, FIRST_STEP, SECOND_STEP, THIRD_STEP, FOURTH_STEP, STOP} state;
always_ff @(posedge clk) begin
light_set = sw;
case (state)
IDLE: state <= INIT;
INIT: begin
state <= FIRST_STEP;
light_set <= ~light_set; // switch active light set
end
FIRST_STEP: begin
if (cnt_phase == 0) begin
state <= SECOND_STEP;
cnt_phase <= DELAY;
end else if (stb) cnt_phase <= cnt_phase - 1;
end
SECOND_STEP: begin
if (cnt_phase == 0) begin
state <= THIRD_STEP;
cnt_phase <= DELAY;
end else if (stb) cnt_phase <= cnt_phase - 1;
end
THIRD_STEP: begin
if (cnt_phase == 0) begin
state <= FOURTH_STEP;
cnt_phase <= DELAY;
end else if (stb) cnt_phase <= cnt_phase - 1;
end
FOURTH_STEP: begin
if (cnt_phase == 0) begin
state <= STOP;
cnt_phase <= DELAY;
light_set <= ~light_set; // switch active light set
end else if (stb) cnt_phase <= cnt_phase - 1;
end
STOP: begin
if (en == 1'b1)
state <= FIRST_STEP;
else
state <= STOP;
end
default: state <= STOP;
endcase
end
// set LEDS based on active light set and state
always_ff @(posedge clk) begin
case (state)
FIRST_STEP: begin
if (light_set == 0) begin
led[0] = 1;
led[1] = 0;
led[2] = 0;
led[3] = 1;
io0 = 1;
io1 = 0;
io2 = 0;
io3 = 1;
end else if (light_set == 1) begin
led[0] = 0;
led[1] = 1;
led[2] = 0;
led[3] = 1;
io0 = 0;
io1 = 1;
io2 = 0;
io3 = 1;
end
end
SECOND_STEP: begin
if (light_set == 0) begin
led[0] = 1;
led[1] = 0;
led[2] = 1;
led[3] = 0;
io0 = 1;
io1 = 0;
io2 = 1;
io3 = 0;
end else if (light_set == 1) begin
led[0] = 0;
led[1] = 1;
led[2] = 1;
led[3] = 0;
io0 = 0;
io1 = 1;
io2 = 1;
io3 = 0;
end
end
THIRD_STEP: begin
if (light_set == 0) begin
led[0] = 0;
led[1] = 1;
led[2] = 1;
led[3] = 0;
io0 = 0;
io1 = 1;
io2 = 1;
io3 = 0;
end else if (light_set == 1) begin
led[0] = 1;
led[1] = 0;
led[2] = 1;
led[3] = 0;
io0 = 1;
io1 = 0;
io2 = 1;
io3 = 0;
end
end
FOURTH_STEP: begin
if (light_set == 0) begin
led[0] = 0;
led[1] = 1;
led[2] = 0;
led[3] = 1;
io0 = 0;
io1 = 1;
io2 = 0;
io3 = 1;
end else if (light_set == 1) begin
led[0] = 1;
led[1] = 0;
led[2] = 0;
led[3] = 1;
io0 = 1;
io1 = 0;
io2 = 0;
io3 = 1;
end
end
STOP: begin
if (light_set == 0) begin
led[0] = 0;
led[1] = 0;
led[2] = 0;
led[3] = 0;
io0 = 0;
io1 = 0;
io2 = 0;
io3 = 0;
end else if (light_set == 1) begin
led[0] = 0;
led[1] = 0;
led[2] = 0;
led[3] = 0;
io0 = 0;
io1 = 0;
io2 = 0;
io3 = 0;
end
end
endcase
end
endmodule
We need some constraints. Save the following as Arty-S7-50-Master.xdc
## Configuration options, can be used for all designs
set_property BITSTREAM.CONFIG.CONFIGRATE 50 [current_design]
set_property CONFIG_VOLTAGE 3.3 [current_design]
set_property CFGBVS VCCO [current_design]
set_property BITSTREAM.CONFIG.SPI_BUSWIDTH 4 [current_design]
set_property CONFIG_MODE SPIx4 [current_design]
## SW3 is assigned to a pin M5 in the 1.35v bank. This pin can also be used as
## the VREF for BANK 34. To ensure that SW3 does not define the reference voltage
## and to be able to use this pin as an ordinary I/O the following property must
## be set to enable an internal VREF for BANK 34. Since a 1.35v supply is being
## used the internal reference is set to half that value (i.e. 0.675v). Note that
## this property must be set even if SW3 is not used in the design.
set_property INTERNAL_VREF 0.675 [get_iobanks 34]
## Clock Signals
set_property -dict { PACKAGE_PIN R2 IOSTANDARD SSTL135 } [get_ports { clk }]; #IO_L12P_T1_MRCC_34 Sch=ddr3_clk[200]
create_clock -add -name sys_clk_pin -period 10.000 -waveform {0 5.000} [get_ports { clk }];
## LEDs
set_property -dict { PACKAGE_PIN E18 IOSTANDARD LVCMOS33 } [get_ports { led[0] }]; #IO_L16N_T2_A27_15 Sch=led[2]
set_property -dict { PACKAGE_PIN F13 IOSTANDARD LVCMOS33 } [get_ports { led[1] }]; #IO_L17P_T2_A26_15 Sch=led[3]
set_property -dict { PACKAGE_PIN E13 IOSTANDARD LVCMOS33 } [get_ports { led[2] }]; #IO_L17N_T2_A25_15 Sch=led[4]
set_property -dict { PACKAGE_PIN H15 IOSTANDARD LVCMOS33 } [get_ports { led[3] }]; #IO_L18P_T2_A24_15 Sch=led[5]
## ChipKit Outer Digital Header
set_property -dict { PACKAGE_PIN L13 IOSTANDARD LVCMOS33 } [get_ports { io0 }]; #IO_0_14 Sch=ck_io[0]
set_property -dict { PACKAGE_PIN N13 IOSTANDARD LVCMOS33 } [get_ports { io1 }]; #IO_L6N_T0_D08_VREF_14 Sch=ck_io[1]
set_property -dict { PACKAGE_PIN L16 IOSTANDARD LVCMOS33 } [get_ports { io2 }]; #IO_L3N_T0_DQS_EMCCLK_14 Sch=ck_io[2]
set_property -dict { PACKAGE_PIN R14 IOSTANDARD LVCMOS33 } [get_ports { io3 }]; #IO_L13P_T2_MRCC_14 Sch=ck_io[3]
## Switches
set_property -dict { PACKAGE_PIN H14 IOSTANDARD LVCMOS33 } [get_ports { sw }]; #IO_L20N_T3_A19_15 Sch=sw[0]
set_property -dict { PACKAGE_PIN H18 IOSTANDARD LVCMOS33 } [get_ports { en }]; #IO_L21P_T3_DQS_15 Sch=sw[1]
Testing the System
Below I show you a video of how this project works.
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