I'm trying to make a morse code display using an led. I need a half second pulse of the light to represent a dot and a 1.5 second pulse to represent a dash.
I'm really stuck here. I have made a counter using an internal 50MHz clock on my FPGA. The machine I have to make will take as input a 3 bit number and translate that to a morse letter, A-H with A being 000, B being 001 and so on. I just need to figure out how to tell the FPGA to keep the led on for the specified time and then turn off for about a second (that would be the delay between a dot pulse and a dash pulse).
Any tips would be greatly appreciated.
Also, it has to be synthesizable.
Here is my code. It's not functioning yet. The error message it keeps giving me is:
Error (10028): Can't resolve multiple constant drivers for net "c3[0]"
at part4.v(149)
module part4 (SELECT, CLK, CLOCK_50, RESET, led);
input [2:0]SELECT;
input RESET, CLK, CLOCK_50;
output reg led=0;
reg [26:0] COUNT=0; //register that keeps track of count
reg [1:0] COUNT2=0; //keeps track of half seconds
reg halfsecflag=0; //goes high every time half second passes
reg dashflag=0; //goes high every time 1 and half second passes
reg [3:0] code; //1 is dot and 0 is dash. There are 4 total
reg [1:0] c3; //keeps track of the index we are on in the code.
reg [3:0] STATE; //register to keep track of states in the state machine
reg done=0; //a flag that goes up when one morse pulse is done.
reg ending=0; //another flag that goes up when a whole morse letter has flashed
reg [1:0] length; //This is the length of the morse letter. It varies from 1 to 4
wire i; // if i is 1, then the state machine goes to "dot". if 0 "dash"
assign i = code[c3];
parameter START= 4'b000, DOT= 4'b001, DASH= 4'b010, DELAY= 4'b011, IDLE=
4'b100;
parameter A= 3'b000, B=3'b001, C=3'b010, D=3'b011, E=3'b100, F=3'b101,
G=3'b110, H=3'b111;
always #(posedge CLOCK_50 or posedge RESET) //making counter
begin
if (RESET == 1)
COUNT <= 0;
else if (COUNT==8'd25000000)
begin
COUNT <= 0;
halfsecflag <= 1;
end
else
begin
COUNT <= COUNT+1;
halfsecflag <=0;
end
end
always #(posedge CLOCK_50 or posedge RESET)
begin
if (RESET == 1)
COUNT2 <= 0;
else if ((COUNT2==2)&&(halfsecflag==1))
begin
COUNT2 = 0;
dashflag=1;
end
else if (halfsecflag==1)
COUNT2= COUNT2+1;
end
always #(RESET) //asynchronous reset
begin
STATE=IDLE;
end
always#(STATE) //State machine
begin
done=0;
case(STATE)
START: begin
led = 1;
if (i) STATE = DOT;
else STATE = DASH;
end
DOT: begin
if (halfsecflag && ~ending) STATE = DELAY;
else if (ending) STATE= IDLE;
else STATE=DOT;
end
DASH: begin
if ((dashflag)&& (~ending))
STATE = DELAY;
else if (ending)
STATE = IDLE;
else STATE = DASH;
end
DELAY: begin
led = 0;
if ((halfsecflag)&&(ending))
STATE=IDLE;
else if ((halfsecflag)&&(~ending))
begin
done=1;
STATE=START;
end
else STATE = DELAY;
end
IDLE: begin
c3=0;
if (CLK) STATE=START;
else STATE=IDLE;
end
default: STATE = IDLE;
endcase
end
always #(posedge CLK)
begin
case (SELECT)
A: length=2'b01;
B: length=2'b11;
C: length=2'b11;
D: length=2'b10;
E: length=2'b00;
F: length=2'b11;
G: length=2'b10;
H: length=2'b11;
default: length=2'bxx;
endcase
end
always #(posedge CLK)
begin
case (SELECT)
A: code= 4'b0001;
B: code= 4'b1110;
C: code= 4'b1010;
D: code= 4'b0110;
E: code= 4'b0001;
F: code= 4'b1011;
G: code= 4'b0100;
H: code= 4'b1111;
default: code=4'bxxxx;
endcase
end
always #(posedge CLK)
begin
if (c3==length)
begin
c3<=0; ending=1;
end
else if (done)
c3<= c3+1;
end
endmodule
I have been reading your code and there are many issues:
The code is not formatted.
You did not provide a test-bench. Did you write one?
"Can't resolve multiple constant drivers for net" Search on stack exchange for the error message. It has been asked many times.
Use always #(*) not e.g. always #(STATE) you are missing signals like i, halfsecflag, ending. But see point 6: You want the STATE in a clocked section.
Where you use always #(posedge CLK) you must use non-blocking assignments: <=.
There are many places where you use always #(posedge CLK) where you want to use always #(*) (e.g. where you set length and code) Opposite you want to use a posedge CLK where you work with your STATE.
Use one clock and one clock only. Do not use CLK and CLOCK_50. Use either one or the other.
Take care of your vector sizes. This 8'd25000000 is wrong as you can no fit 25000000 in 8 bits.
Your usage of halfsecflag is excellent! I have see many times where people think they can use always #(halfsecflag) which is a recipe for disaster!
Below you find a small piece of your code which I have re-written.
All assignments are non-blocking <=
halfsecflag is essential to operate the code only every half a second, so I put that by itself in a separate if at the top. I would use that throughout the code.
All register are reset, both COUNT2 and dashflag.
dashflag was set to 1 but never set back to 0. I fixed that.
I specified the vector sizes. It makes the code "Lint proof".
Here is it:
always #(posedge CLOCK_50 or posedge RESET)
begin
if (RESET == 1'b1)
begin
COUNT2 <= 2'd00;
dashflag <= 1'b0;
end // reset
else if (halfsecflag) // or if (halfsecflag==1'b1)
begin
if (COUNT2==2'd2))
begin
COUNT2 <= 2'd0;
dashflag <=1'b1;
end
else
begin
COUNT2 <= COUNT2+2'd1;
dashflag <=1'b0;
end
end // clocked
end // always
Start fixing the rest of your code the same way. Write a test-bench, simulate and trace on a waveform display where things go wrong.
Normally you would build the finite state machine to produce the output. That machine would have some stages, like reading the input, mapping it to a sequence of morse code element, shifting out the elements to output buffer, waiting for conditions to move to the next morse element. You will need some timer that would produce one morse time unit intervals, and depending on the FSM stage you will wait one, three or seven time units. The FSM will spin in the waiting stage, it doesn't "magically" sleeps in some fpga-produced delay, there's no such things.
Okay a year later, I know exactly what one should do if they want to create a delay in their verilog program! Essentially, what you should do is create a timer using one of the clocks on your FPGA. For me on my Altera DE1-SoC, the timer I could use is the 50MHz clock known as CLOCK_50. What you do is make a timer module that triggers on the positive (or negative, doesn't matter) edge of the 50MHz clock. Set up a count register that holds a constant value. For example, reg [24:0] timer_limit = 25'd25000000; This is a register that can hold 25 bits. I've set this register to hold the number 25 million. The idea is to flip a bit every time the value in this register is exceeded. Here's some pseudocode to help you understand:
//Your variable declarations
reg [24:0] timer_limit = 25'd25000000; //defining our timer limit register
reg [25:0] timer_count = 0; //See note A
reg half_sec_clock;
always#(posedge of CLOCK_50) begin
if timer_count >= timer_limit then begin
reset timer_count to 0;
half_sec_clock = ~half_sec_clock; //toggle your half_sec_clock
end
Note A: Setting it to zero may or may not initialize count, it's always best to include a reset function that clears your count to zero because you don't know what the initial state is when you're dealing with hardware.
This is the basic idea of how to introduce timing into your hardware. You need to use an onboard clock on your device, trigger on the edge of that clock and create your own slower clock to measure things like seconds. The example above will give you a clock that triggers periodically every half second. For me, this allowed me to easily make a morse code light that could flash on either 1 half second count, or 3 half seconds. My best advice to you beginners is to work in a modular fashion. For example build your half second clock and then test it out to see if you can get a light on your FPGA to toggle once every half second (or whatever interval you want). :) I really hope this is the answer that helps you. I know this is what I was looking for when I originally posted this question so long ago.
Related
I have a question about using timers and clocks in Verilog. I want to set up a custom reg to compare to an accumulator, which will control the state of an LED. The board uses inverse logic, so 0 is high on the LED. There are a few concepts I just need some clarification on. The clock is 100 MHz.
always #(posedge clk100 or negedge reset_)
begin
cust_LED_counter <= (cust_LED_counter<cust_LED_timer) ? cust_LED_counter + 1'b1 : 16'd0;
cust_LED_timer1 <= (cust_LED_counter == cust_LED_timer);
if(!reset_)
begin
cust_LED1 <= 'b0;
cust_LED_timer <= 'd0;
cust_LED_timer1 <= 'd0;
end
else
begin
cust_LED1 <= ~cust_LED_timer1;
end
end
For the accumulator, what is the action that resets it and allows for blinking to happen? Would it not hit the cust_LED_timer value and stay at that high reading?
I think I'm misunderstanding how a FPGA clock operates. Assuming this would cause a blinking action in the LED, it would mean some timer hit the upper limit and reset; however, I'm not sure if this would take place in the counter portion of the code, or instead would occur where the clock/reset is defined.
Also, based on how this layout looks it wouldn't be a uniform blink, in terms of equal time on and off. Is there a way to implement such a system for custom input?
Here's a simple module that should blink the LED with a 50-50 duty cycle for an arbitrary number of clocks (up to 2^26)
module blink(input clk, input rst, input [25:0] count_max, output LED);
reg [25:0] counter, next_count;
assign LED = counter < count_max >> 1;
always #(posedge clk or posedge rst)
begin
if (rst)
counter <= 0;
else
counter <= next_count;
end
always #* begin
if (counter < count_max - 1)
next_count = counter + 1;
else
next_count = 0;
end
endmodule // blink
Let me know if this doesn't compile! I don't have a verilog compiler where I'm writing this from at the moment!
module clks(
input clk,
output [15:0] led
);
wire div2, div4, div8;
reg [2:0] count = 0;
assign div2 = count[0];
assign div4 = count[1];
assign div8 = count[2];
always #(posedge clk) count = count + 1;
endmodule
How can I turn on each led (I have 15 leds) using clock?
I'm really having trouble finding helpful resources online
initial begin
case({count})
2'b00:
led = 15'b000000000000001;
2'b01:
led = 15'b000000000000010;
...
endcase
end
This didn't work.
Or could I do something like this?
led = led + 1;
In your sample code above, you defined count as 3 bits, but your case statements are 2 bits wide. Also, you don't want the initial statement, rather use an always statement.
always # (count)
begin
case(count)
3'b000 : led = 15'b000_0000_0001;
3'b001 : led = 15'b000_0000_0010;
...
endcase
end
I guess that 'by using clock' means changing the led every clock cycle, right? Also it looks like you are trying to encode the led sequentially. In this case you can do the following:
you need to reset your lead to an initial value, sey 15'b1;
every clock cycle you can just shift it left by one. You should not do it in an initial block (though there is a technical way to do so). Use always blocks:
Here is an example:
module clks(
input clk,
input reset,
output reg [15:0] led
);
always #(posedge clk) begin
if (reset == 1)
led <= 15'b1;
else
led <= led << 1;
end
endmodule
In the above case '1' will travel through all bits of led over 15 clock cycles once. 'led' will become '0' after this. You have to make sure that it becomes '1' again if you want to continue in cycles.
Another possibility is to initialize 'led' in the always block, but it is not always synthesizable. YOu do not need a reset signal here.
initial led = 15'b1;
always #(posedge clk) led <= led << 1;
I was following a tutorial on SPI master in Verilog. I've been debugging this for about three hours now and cannot get it to work.
I've been able to break down the issue into a minimum representative issue. Here are the specifications:
We have two states, IDLE and COUNTING. Then, on the clock positive edge, we check:
If the state is IDLE, then the counter register is set to 0. If while in this state the dataReady pin is high, then the state is set to COUNTING and the counter is set to all 1s.
If the state is COUNTING, the state remains COUNTING as long as counter is not zero. Otherwise, the state is returned to IDLE.
Then, we count on the negative edge:
On the negative edge of clock if state is COUNTING, then decrement counter.
Here's the code I came up with to fit this specification:
// look in pins.pcf for all the pin names on the TinyFPGA BX board
module top (
input CLK, // 16MHz clock
input PIN_14,
output LED, // User/boot LED next to power LED
output USBPU // USB pull-up resistor
);
// drive USB pull-up resistor to '0' to disable USB
assign USBPU = 0;
reg [23:0] clockDivider;
wire clock;
always #(posedge CLK)
clockDivider <= clockDivider + 1;
assign clock = clockDivider[23];
wire dataReady;
assign dataReady = PIN_14;
parameter IDLE = 0, COUNTING = 1;
reg state = IDLE;
reg [3:0] counter;
always #(posedge clock) begin
case (state)
IDLE: begin
if (dataReady)
state <= COUNTING;
end
COUNTING: begin
if (counter == 0)
state <= IDLE;
end
endcase
end
always #(negedge clock) begin
if (state == COUNTING)
counter <= counter - 1;
end
always #(state) begin
case (state)
IDLE:
counter <= 0;
COUNTING:
counter <= counter;
endcase
end
assign LED = counter != 0;
endmodule
With this, we get the error:
ERROR: multiple drivers on net 'LED' (LED_SB_DFFNE_Q.Q and LED_SB_DFFNE_Q_1.Q)
Why? There is literally only one assign statement on the LED.
First of all it would not be easy to come up with a synthesizable model in such a case. But, you do not need any negedge logic to implement your model. Also you made several mistakes and violated many commonly accepted practices.
Now about some problems in your code.
By using non-blocking assignment in the clock line you created race condition in the simulation which will probably cause incorrect simulation results:
always #(posedge CLK)
clockDivider <= clockDivider + 1; // <<< this is a red flag!
assign clock = clockDivider[23];
...
always #(posedge clk)
you incorrectly used nbas in your always block
always(#state)
... counter <= conunter-1; // <<< this is a red flag again!
your state machine has no reset. Statements like reg state = IDLE; will only work in simulation and in some fpgas. It is not synthesizable in general. I suggest that you do not use it but provide a reset signal instead.
Saying that, i am not aware of any methodology which would use positive and negative edges in such a case. So, you should not. All your implementation can be done under the posedge, something like the following. However
always #(posedge clock) begin
if (reset) begin // i suggest that you use reset in some form.
state <= IDLE;
counter <= 0;
end
else begin
case (state)
IDLE: begin
if (dataReady) begin
state <= COUNTING;
counter <= counter - 1;
end
end
COUNTING: begin
if (counter == 0)
state <= IDLE;
else
counter <= counter - 1;
end
endcase
end
end
I hope i did it right, did not test.
Now you do not need the other two always blocks at all.
I'm trying to implement a morse code display on my FPGA. I've written a lot of code but I keep getting the same error message. Before I get into that though, please take a look at the assignment. To be clear, I'm not asking for someone to do the assignment for me. I just need help debugging my code.
"Part IV
In this part of the exercise you are to implement a Morse-code encoder using an FSM. The Morse code uses patterns of short and long pulses to represent a message. Each letter is represented as a sequence of dots (a short
pulse), and dashes (a long pulse). For example, the first eight letters of the alphabet have the following representation:
A • —
B — • • •
C — • — •
D — • •
E •
F • • — •
G — — •
H • • • •
Design and implement a Morse-code encoder circuit using an FSM. Your circuit should take as input one of
the first eight letters of the alphabet and display the Morse code for it on a red LED. Use switches SW2−0 and
pushbuttons KEY1−0 as inputs. When a user presses KEY1, the circuit should display the Morse code for a letter
specified by SW2−0 (000 for A, 001 for B, etc.), using 0.5-second pulses to represent dots, and 1.5-second pulses
to represent dashes. Pushbutton KEY0 should function as an asynchronous reset.
Here is the code I have written:
module part4 (SELECT, button, CLOCK_50, RESET, led);
input [2:0]SELECT;
input RESET, button, CLOCK_50;
output reg led=0;
reg [26:0] COUNT=0; //register that keeps track of count
reg [1:0] COUNT2=0; //keeps track of half seconds
reg halfsecflag=0; //goes high every time half second passes
reg dashflag=0; // goes high every time 1 and half second passes
reg [3:0] code; //1 is dot and 0 is dash. There are 4 total
reg [1:0] c3=2'b00; //keeps track of the index we are on in the code.
reg [2:0] STATE; //register to keep track of states in the state machine
wire done=0; //a flag that goes up when one morse pulse is done.
reg ending=0; //another flag that goes up when a whole morse letter has
flashed
reg [1:0] length; //This is the length of the morse letter. It varies from 1
to 4
wire i; // if i is 1, then the state machine goes to "dot". if 0 "dash"
assign i = code[c3];
assign done= (halfsecflag)&&(~ending)&&~led;
parameter START= 3'b000, DOT= 3'b001, DASH= 3'b010, DELAY= 3'b011, IDLE=
3'b100;
parameter A= 3'b000, B=3'b001, C=3'b010, D=3'b011, E=3'b100, F=3'b101,
G=3'b110, H=3'b111;
always #(posedge CLOCK_50 or posedge RESET) //making counter
begin
if (RESET == 1)
COUNT <= 0;
else if (COUNT==25'd25000000)
begin
COUNT <= 0;
halfsecflag <= 1;
end
else
begin
COUNT <= COUNT+1;
halfsecflag <=0;
end
end
always #(posedge CLOCK_50 or posedge RESET)
begin
if (RESET == 1)
begin
COUNT2 <= 2'd00;
dashflag<=1'b0;
end
else if ((COUNT2==2)&&(halfsecflag))
begin
COUNT2 <= 2'd0;
dashflag<=1'b1;
end
else if ((halfsecflag)&&(COUNT2!=2))
begin
COUNT2<= COUNT2+2'd1;
dashflag<=1'b0;
end
end
always #(posedge button or RESET) //asynchronous reset
begin
STATE<=IDLE;
end
always#(*) begin //State machine
case (STATE)
START: begin
led <= 1;
if (i) STATE <= DOT;
else STATE <= DASH;
end
DOT: begin
if (halfsecflag && ~ending) STATE <= DELAY;
else if (ending) STATE<= IDLE;
else STATE<=DOT;
end
DASH: begin
if ((dashflag)&& (~ending))
STATE <= DELAY;
else if (ending)
STATE <= IDLE;
else STATE <= DASH;
end
DELAY: begin
led <= 0;
if ((halfsecflag)&&(ending))
STATE<=IDLE;
else if ((halfsecflag)&&(~ending))
STATE<=START;
else STATE <= DELAY;
end
IDLE: begin
c3<=2'b00;
if (button) STATE<=START;
STATE<=IDLE;
end
default: STATE <= IDLE;
endcase
end
always #(posedge button)
begin
case (SELECT)
A: length<=2'b01;
B: length<=2'b11;
C: length<=2'b11;
D: length<=2'b10;
E: length<=2'b00;
F: length<=2'b11;
G: length<=2'b10;
H: length<=2'b11;
default: length<=2'bxx;
endcase
end
always #(posedge button)
begin
case (SELECT)
A: code<= 4'b0001;
B: code<= 4'b1110;
C: code<= 4'b1010;
D: code<= 4'b0110;
E: code<= 4'b0001;
F: code<= 4'b1011;
G: code<= 4'b0100;
H: code<= 4'b1111;
default: code<=4'bxxxx;
endcase
end
always #(*)
begin
if (c3==length)
begin
c3=2'b00; ending<=1;
end
else if (done)
c3= c3+2'b01;
end
endmodule
The error code I keep getting is Error (10028): Can't resolve multiple constant drivers for net "c3[1]" at part4.v(68)
Also in green above this error code, it says inferred latch a few different times. This doesn't seem good! Can you take a look at my code and see if you can figure out why I'm getting this error message?
Update: This is not a duplicate of my previous question. Before I was asking for tips on how to create a delay using verilog. In this question I was asking for help debugging my code. The error message I got was not making sense to me. I looked at the other answers on stack exchange regarding that error code but none of them made sense to me.
You're missing a couple of (very) basic principles - you can't code hardware without them. Note that I'm using VHDL terminology here ('signal'/'process'/etc), but the idea is exactly the same in Verilog, if a little harder to find the right words.
You can only drive a signal from a single process (if you're synthesising, anyway), or you get multiple drivers. Look at c3 - where is it driven? You're driving it from 2 combinatorial always blocks. The same is true of STATE.
In a combinatorial process, if you read one of your output (driven) signals before you assign to it (drive it), you're inferring memory. This is where your inferred latches are coming from. Think about it - a process "wakes up" when something it is sensitive to changes/fires. If it then reads the value of a signal that it itself drives, this must mean that the signal has to be recorded somewhere in order for it have a current value; it must know what value it had when the process last completed. This is what memory means. You do this for both STATE and c3 (if(c3==length) must read c3, case STATE must read state).
You fix (1) by recoding so that all signals are driven from only one 'owner' process.
Fixing (2) is more difficult. In a combinatorial process (alway #*) make sure you either give all outputs default values first, or make sure that you never read anything before you've written it, so that there's no confusion about whether memory is inferred. Your combinatorial process to derive STATE is wrong. You read STATE, and then write it. You should have 2 signals: current state, and next state. You should read the current state, and create the next one.
You've got other problems, but you need to fix those 2 first.
Hello Friends I still not know how to Generate Delay in Verilog For synthesis and call it any line in Verilog for synthesis...for finding this I write a code but it not works please help me if you know how to Generate Delay and call in any line like a C's Function*......Actually Friends if you tell me why I use for Loop here then my answer is - I want to move pointer inside for loop until and unless they completes its calculation that I made for Delay Generation..
module state_delay;
reg Clk=1'b0;
reg [3:0]stmp=4'b0000;
integer i,a;
always
begin
#50 Clk=~Clk;
end
always #(posedge Clk)
begin
a=1'b1;
delay();
a=1'b0;
delay();
a=1'b1;
end
task delay();
begin
for(i=0;i==(stmp==4'b1111);i=i+1)
begin
#(posedge Clk)
begin
stmp=stmp+1;
end
end
if(stmp==4'b1111)
begin
stmp=4'b0000;
end
end
endtask
endmodule
Actually friends I want this a=1'b0; delay(); a=1'b1; please help I already tried delay Generation Using Counter previously but it not works for me.....If you know same using Counter then please tell me......Thanks
// will generate a delay of pow(2,WIDTH) clock cycles
// between each change in the value of "a"
`define WIDTH 20
reg [`WIDTH:0] counter;
wire a = counter[`WIDTH];
always #(posedge Clk)
counter <= counter + 1;
You have to choose a suitable value for WIDTH according to how much delay you want between changes in a and the rate of your Clk signal
This question is a more succinct version of How to generate delay in verilog using Counter for Synthesis and call inside Always block?.
There is one section of code that I find troublesome:
always #(posedge Clk) begin
a = 1'b1;
delay() ;
a = 1'b0;
end
NB: A good rule to stick to is to always use <= in edge triggered processes.
for now lets think of the delay(); task as #10ns; What we get with the current code would be:
time 0ns a = x;
time 1ns a = 1; //Posedge of clk
time 6ns a = 1; //Waiting on delay
time 11ns a = 0; //Delay completed
Using <= and I think you should see a similar behaviour. However when it comes to synthesis delays like #1ns can not be created and the whole thing will collapse back down to :
always #(posedge Clk) begin
a <= 1'b0;
end
With a hardware description language a good approach is to consider what hardware we want to imply and describe it in the language. The construct always #(posedge Clk) is used to imply flip-flops, that is the output changes once per clock cycle. In the question we have a changing value 3 times, from 1 clock edge I do not know what hardware you are trying to imply.
You can not provide an inline synthesizable delay. For always #(posedge clk) blocks to be synthesizable they should be able to execute in zero time. You need to introduce a state machine to keep state between clock edges. I think I have already provided a good example on how to do this in my previous answer. If the delay is to be programmable then see mcleod_ideafix's answer.