Verilog Error
I am trying to learn verilog . This code is made for seven segment led using counter. But I am not able to assign value to nr it gives error. I made a state machine and wish to get next number on seven segment led after each positive clock.
/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa/
module LED ( nr,clk);
input clk;
output [6:0]nr; //output led seven bit number
reg [6:0]nr;
reg [2:0]state;
always #(posedge clk);
begin
state <= 3'b000; // assigning at each clock
case (state)
3'b000:
begin
nr <= 7'b0000001;
state <= 3'b001;
end
3'b001:
begin
nr <= 7'b0011111;
state <= 3'b010;
end
3'b010:
begin
nr <= 7'b0100101;
state <= 3'b011;
end
3'b011:
begin
nr <= 7'b0001100;
state <= 3'b100;
end
3'b100:
begin
nr <= 7'b1011010;
state <= 3'b101;
end
3'b101:
begin
nr <= 7'b1001000;
state <= 3'b110;
end
3'b110:
begin
nr <= 7'b1000000;
state <= 3'b111;
end
3'b111:
begin
nr <= 7'b0011101;
state <= 3'b000;
end
end
endmodule
always #(posedge clk) no semicolon!
Related
For a lab I must create the logic to use on a Digilent PMOD ALS. In the lab requirenment I cannot use the sclk signal on the sensitivity list and therefore use a state machine to create the 2.5 MHz clk signal to send to the PMOD ALS. See the code below:
module sens_interface(
input clk, //clk 10Mhz
input reset_n,
input [15:0] delay,
input datain,
output reg sclk,
output reg cs_n,
output reg [3:0] Cout,
output reg [3:0] Dout,
output reg [5:0] cnt
);
//params
//state machine 1
parameter SA0 = 3'b000;
parameter SA1 = 3'b001;
parameter SA2 = 3'b010;
parameter SA3 = 3'b011;
parameter SD0 = 3'b100;
parameter SD1 = 3'b101;
//state machine 2
parameter SR0 = 2'b00;
parameter SR1 = 2'b01;
parameter SR2 = 2'b10;
parameter SR3 = 2'b11;
//pmod als registers
//reg sclk; //2.5Mhz clk
//reg cs_n; //
reg [14:0] data_reg;
//count registers
//reg [5:0] cnt;
reg [15:0] cnt_d;
reg [5:0] cnt_r;
//state registers
reg [2:0] state_sclk;
reg [1:0] state_data;
//State Machine 1
always # (posedge clk)begin
if(reset_n == 1'b0)begin
cs_n <= 1'b1;
sclk <= 0;
cnt <= 6'd0;
cnt_d <= 16'd0;
end
else
case(state_sclk)
SA0:begin
sclk <= 1'b1;
state_sclk <= SA1;
if (cnt <= 6'd17)
cs_n <= 1'b0;
else
cs_n <= 1'b1;
end
SA1:begin
state_sclk <= SA2;
end
SA2:begin
sclk <= 1'b0;
cnt <= cnt + 1;
state_sclk <= SA3;
end
SA3:begin
if(cnt == 6'd21)begin
cnt <= 0;
state_sclk <= SD0;
end
else
state_sclk <= SA0;
end
SD0:begin
cnt_d <= delay;
state_sclk <= SD1;
end
SD1:begin
if (cnt_d == 0)
state_sclk <= SA0;
else
cnt_d <= cnt_d - 1;
end
default:begin
state_sclk <= SA0;
end
endcase
end
always # (posedge clk)begin
if (reset_n == 1'b0)begin
cnt_r <= 0;
data_reg <= 0;
end
else begin
case (state_data)
SR0:begin
if (cs_n == 1'b1 && sclk == 1'b1)
state_data <= SR1;
end
SR1: begin
if (cs_n == 1'b1)begin
state_data <= SR0;
cnt_r <= 0;
end
else if (sclk == 1'b0)
state_data <= SR2;
end
SR2:begin
if (cs_n == 1'b1)begin
state_data <= SR0;
cnt_r <= 0;
end
else if (cnt_r == 15)
state_data <= SR3;
else if (sclk == 1'b1)begin
data_reg [14-cnt_r] <= datain;
cnt_r <= cnt_r + 1;
state_data <= SR1;
end
end
SR3:begin
if (cs_n == 1) begin
Cout <= data_reg [11:8];
Dout <= data_reg [7:4];
state_data <= SR0;
end
end
default:begin
state_data <= SR0;
end
endcase
end
end
endmodule
I tried to make a simulation of it and the simulation indicates that after my cnt register reaches 15 it just cuts out and goes to 0.
simulation
That behavior is caused by your SA3 state.
SA3:begin
if(cnt == 6'd21)begin
cnt <= 0;
state_sclk <= SD0;
end
else
state_sclk <= SA0;
end
end
When your cnt == 6'd21 (which is 6'h15) the cnt is set to zero.
The generic variable names and lack of comments makes it difficult to see why this is not the expected behavior.
I have created a counter that counts up to 30. I have an output signal out. At two particular counts, i.e., when counter reaches 10 (first) and when counter reaches 15 (second), I want the output to become low. Somehow I'm missing a basic logic here as only at one particular count (either at 10 or 15) I'm able to make the output zero.
Here is the code
module user_def_pulse(
output integer counter,
output reg out,
input clk, reset
);
parameter no_of_counts = 30;
parameter first = 10;
parameter second = 15;
initial
begin
counter = 0;
out = 1'b0;
end
always #(posedge clk)
begin
if (reset)
begin
counter <= 1'b0;
end
else if (counter == no_of_counts)
begin
counter <= 1'b0;
out <= 1'b0;
end
else
begin
if ((counter == first) || (counter == second))
out <= 1'b0;
else
begin
counter <= counter + 1;
out <= 1'b1;
$display($time," The value of counter is %d", counter);
end
end
end
endmodule
Here is the test bench
module user_def_pulse_tb(
);
parameter time_period = 10;
wire [31:0] COUNTER;
wire OUT;
reg CLK, RESET;
user_def_pulse udp1 (.counter(COUNTER), .out(OUT), .clk(CLK), .reset(RESET));
initial
begin
CLK = 1'b0;
RESET = 1'b1;
#20 RESET = 1'b0;
end
always
#time_period CLK = ~CLK;
endmodule
Here is the output waveform.
The problem with your code is that is stops incrementing the counter as soon as it hits the first value. You need to keep incrementing the counter. I moved the increment outside of the if ((counter == first) || ... clause.
always #(posedge clk) begin
if (reset) begin
counter <= 1'b0;
end else if (counter == no_of_counts) begin
counter <= 1'b0;
out <= 1'b0;
end else begin
counter <= counter + 1;
$display($time," The value of counter is %d", counter);
if ((counter == first) || (counter == second)) begin
out <= 1'b0;
end else begin
out <= 1'b1;
end
end
end
I am trying to write a Finite State Machine for an assignment. However, I don't understand what is wrong with my module code. I get the error:
ERROR VCP5221 "Illegal reference to memory: st." "design.sv" 77 5
when I try to synthesize. I think I've either misunderstood how switch-case is used in Verilog or I've attempted to make an illegal assignment inside the switch-case but I don't know how to find it.
//Code here
module MooreFSM(
input clk,
input in,
output out
);
reg state[2:0];
reg sel[2:0];
reg o;
assign out = o;
initial begin
state <= 3'b000;
o <= 1'b0;
end
always#(negedge clk) begin
state <= sel;
end
always#(posedge clk) begin
case(state)
3'b000: begin
if(in == 1'b0) begin
sel <= 3'b010;
o <= 1'b0;
end
else if(in == 1'b1) begin
sel <= 3'b001;
o <= 1'b0;
end
end
3'b001: begin
if(in == 1'b0) begin
sel <= 3'b000;
o <= 1'b0;
end
else if(in == 1'b1) begin
state <= 3'b011;
o <= 1'b0;
end
end
3'b010: begin
if(in == 1'b0) begin
sel <= 3'b100;
o <= 1'b0;
end
else if(in == 1'b1) begin
sel <= 3'b000;
o <= 1'b0;
end
end
3'b011: begin
if(in == 1'b0) begin
sel <= 3'b000;
o <= 1'b1;
end
else if(in == 1'b1) begin
sel <= 3'b011;
o <= 1'b1;
end
end
3'b100: begin
if(in == 1'b0) begin
sel <= 3'b100;
o <= 1'b1;
end
else if(in == 1'b1) begin
sel <= 3'b000;
o <= 1'b1;
end
end
default: begin
sel <= 3'b000;
o <= 1'b0;
end
endcase
end
endmodule
Please help me identify the problem, or if I need to use a different method to synthesize a mux.
I think when you put
else if(in == 1'b1) begin
state <= 3'b011;
o <= 1'b0;
end
you might have meant to write
else if(in == 1'b1) begin
sel <= 3'b011;
o <= 1'b0;
end
By putting state as something being assigned in just one case of this switch statement, you're implicitly asking for it to be latched back to in every other case, which conflicts with you explicitly making it a flop above.
I'm implementing a repeating bit shifter for a 16 bit number. To do this, I have a bit counter that counts how many times I've shifted and resets when I reach 4'b1111. Then I have an assign statement that feeds the MSB to an output. However, the logic makes it so that the output skips the first MSB every time. What is the most succinct way to include the first MSB, before any shifting has occurred?
CODE
module DAC_Control(
input [15:0]data_in,
input clk,
input rst,
output data_out,
output reg cs,
output reg enable
);
//bit counter
reg [3:0] bit_counter;
//to help with shifting
reg [15:0] shifter;
always #(data_in)
shifter <= data_in;
//shifter
always #(posedge (clk)) begin
if (rst) begin
bit_counter <= 4'b0;
enable <= 1'b0;
cs <= 1'b1;
end
else if (bit_counter == 4'b1111) begin
bit_counter <= 4'b0;
enable <= 1'b1;
cs <= 1'b1;
end
else begin //this is the problem area
bit_counter <= bit_counter + 1'b1;
enable <= 1'b0;
cs <= 1'b0;
shifter <= shifter << 1;
end
end
assign data_out = shifter[15];
endmodule
Firstly it would be better to have a trigger to capture the data_in. If not then in simulation ,if the data_in changes in between the shifting it will update the shifter and cause the expected output to change. It would be preferable to capture the data_in based on a qualifying event ( e.g. counter_enable in the example below) . Synthesis will produce an error as shifter has two drivers . One the continuous assignment shifter <= data_in; and other the shifting logic shifter <= shifter << 1;
Updated sample code should serialize the data.
module DAC_Control(
input [15:0]data_in,
input counter_enable,
input clk,
input rst,
output data_out,
output reg cs,
output reg enable
);
//bit counter
reg [3:0] bit_counter;
//to help with shifting
reg [15:0] shifter;
//shifter
always #(posedge (clk)) begin
if (rst) begin
bit_counter <= 4'b0;
shifter <= 0;
end
else if (counter_enable == 1) begin
shifter <= data_in;
bit_counter <= 4'b0;
end
else begin
shifter <= shifter << 1; // shifting
bit_counter <= bit_counter + 1'b1; // counter
end
end
always #(posedge (clk)) begin
if (rst) begin
enable <= 1'b0;
cs <= 1'b1;
end
else if (bit_counter == 4'b1111) begin
enable <= 1'b1;
cs <= 1'b1;
end
else begin
enable <= 1'b0; // generate enable signals
cs <= 1'b0;
end
end
assign data_out = shifter[15];
endmodule
So i am currently doing a little project involving a hd44780 display. But since i want to write my own init sequence i decided to use a state machine. I am quite new to FPGAs an their programming coming from a Java background.
This is my State machine Block.
I this state it works and the IDE doesnt show any errors.
always #(posedge reset)
begin
en_timeout <= 2'b00;
timeout <= 14'b00000000000000;
init <= 4'b000;
data <= 8'b00000000;
en <= 1'b1; //active low
rs <= 1'b0;
rw <= 1'b0;
state <= 4'b0000;
next_state <= 4'b0000;
debug <= 1'b0;
end
if(timeout == 0)
begin //Begin of Initiation state machine
case(state)
s0:
begin
end
s1:
begin
end
s2:
begin
end
s3:
begin
end
s4:
begin
end
s5:
begin
end
s6:
begin
end
s7:
begin
end
s8:
begin
end
s9:
begin
end
s10:
begin
end
normal:
begin
end
endcase
end //End of Initiation state machine
But if i add any assignment between the begin and end of one of the states it shows me "Line n: Syntax error near "<="."
for example:
case(state)
s0:
begin
state <= s1;
end
Full code of my DisplayDriver so far:
module DisplayDriver(
output reg [8:0] data,
output reg en,
output reg rs,
output reg rw,
output reg debug,
input clk,
input reset
);
parameter s0=0,s1=1,s2=2,s3=3,s4=4,s5=5,s6=6,s7=7,s8=8,s9=9,s10=10,normal = 11;
reg [3:0] state; // 4 bit for max 11 combinations s0-s10 and normal
reg [3:0] state; // 4 bit for max 11 combinations s0-s10 and normal [next State]
reg [1:0] en_timeout; // 2 bit for en high to low to high cylce
reg [13:0] timeout; // 14 bit
initial
// begin init
begin
en_timeout <= 2'b00;
timeout <= 14'b00000000000000;
init <= 4'b000;
data <= 8'b00000000;
en <= 1'b1; //active low
rs <= 1'b0;
rw <= 1'b0;
state <= 4'b0000;
next_state <= 4'b0000;
debug <= 1'b0;
end
// end of init
always #(posedge clk)
//begin of everything that needs the clock
begin
if(en_timeout > 0) //begin timeout stack
begin
en_timeout <= en_timeout -1;
en <= ~en;// if en_timeout = 2 -> en = 0; if en_timeout = 1 -> en = 1;
end
else if (timeout > 0) timeout <= timeout -1; //end timeout stack
if(timeout == 0)state <= next_state;
end //end of everything that needs the clock
always #(posedge reset)
begin
en_timeout <= 2'b00;
timeout <= 14'b00000000000000;
init <= 4'b000;
data <= 8'b00000000;
en <= 1'b1; //active low
rs <= 1'b0;
rw <= 1'b0;
state <= 4'b0000;
next_state <= 4'b0000;
debug <= 1'b0;
end
if(timeout == 0)
begin //Begin of Initiation state machine
case(state)
s0:
begin
end
s1:
begin
end
s2:
begin
end
s3:
begin
end
s4:
begin
end
s5:
begin
end
s6:
begin
end
s7:
begin
end
s8:
begin
end
s9:
begin
end
s10:
begin
end
normal:
begin
end
endcase
end //End of Initiation state machine
endmodule
Does anyone have an idea why it behaves this way?
I assume that you are trying to synthesize a register for "state", in which case the update "<=" needs to be inside always (#posedge clk).