I wrote this Verilog code on modelSim.
module my_fsm (clock , reset , in , out);
input clock , reset , in;
output out;
wire clock , reset , in;
reg out;
reg [1:0] state; // state of the machine in case reset = 0
// A = 00 , B = 01 , C = 10 , D = don't care = 11
always #(posedge clock) begin
if (reset == 1'b1)
begin
state <= 2'b00;
out <= 1'b0;
end
else
begin
case (state)
2'b00:
out <= 1'b0;
if (in == 1'b1) state <= 2'b01;
2'b01:
out <= in;
if (in == 1'b0) state <= 2'b10;
if (in == 1'b1) state <= 2'b00;
2'b10:
out <= 1'b1;
if (in == 1'b0) state <= 2'b01;
default: out <= 1'bX;
endcase
end
end
endmodule
But the compiler is giving me this compilation errors:
** Error: (vlog-13069) C:/Users/michael/Documents/Logic Design/hw1/my_fsm .v(22): near "if": syntax error, unexpected if.
** Error: (vlog-13069) C:/Users/michael/Documents/Logic Design/hw1/my_fsm .v(27): near "2": syntax error, unexpected INTEGER NUMBER.
** Error: (vlog-13069) C:/Users/michael/Documents/Logic Design/hw1/my_fsm .v(30): near "default": syntax error, unexpected default.
I have looked up for those problems but couldn't find any solution for them.
Thank you,
Michael
Multiple statements in a branch of a case statement should be enclosed between begin and end. (Just like in an if statement, just like you've done in your if (reset == 1'b1) statement.)
Related
I'm trying to simulate a pulse width modulate (PMW) waveform generator and getting a syntax error in ISE. Checked fuse.xmsgs and found out it's near counter. Can someone point out the syntax error, please?
library IEEE;
use IEEE.STD_LOGIC_1164.all;
use IEEE.numeric_std.all;
entity pwm_gen is
port
(
clock, reset : in std_logic;
width : in std_logic_vector(7 downto 0);
pwm : out std_logic);
end pwm_gen;
architecture bhv of pwm_gen is
type counter is range 0 to 255;
counter count := 0;
begin
process (clock)
begin
if (reset = '1') then
count <= 0;
elsif (clock'event and clock = '1') then
if (count <= width) then
count <= count + 1;
pwm <= '1';
else
count <= count + 1;
pwm <= '0';
end if;
end if;
end process;
end bhv;
counter count := 0;
This is illegal syntax, as you didnt declare the object class (signal, constant, variable). You need to use the format:
signal count : counter := 0
This is also illegal, as you are comparing an integer to a std_logic_vector that you havent included a package for. You need to convert the slv to an unsigned
if (count <= unsigned(width)) then
And finally, reset is missing from the sensitivity list
so I seem to be having a problem in regards to flag signal getting asserted. So basically I am implementing i2c interface between 2 fpga's. My master will send over 50 bytes. On my slave side I want to store the byte coming in into an array. So I check when ever the whole byte is read and available i put it into an array. Now the problem is that after i fill up the whole array i want to assert a signal that should activate a process. My problem is that when the signal is asserted and the process is activated that that I am stuck in the idle loop forever, which confuses me because I was under the assumption that when i enter the process and check the flag signal assertion condition that it is suppose to be high. So is the problem that my signal is not activating the process or is my problem that the by the time i check the flag assertion conditional that the flag already went back to 0?
I have attached some code:
signal i : integer range 0 to 49 := 0;
type field_array is array(0 to 49) of std_logic_vector(7 downto 0);
begin
process(clk,rst)
begin
if( rst = '1') then
i <= 0;
elsif (rising_edge(clk)) then
if(data_available = '1') then
array_of_data(i) <= Master_Data;
i <= i + 1;
end if;
if(i = 49) then
i <= 0; -- reset index back to zero
end if;
end if;
end process;
flag <= '1' when i = 49 else '0';
process(state,flag)
begin
next_state <= state;
case (state) is
when idle =>
if(flag = '1') then
next_state <= Send_data;
end if;
when Send_data =>...
There is a bounds check failure on your assignment, i <= i+1;. It is trying to evaluate it before the check that is performed later (if i=49...).
Change the synchronous part of you code to:
elsif rising_edge(clk) then
if data_available = '1' then
array_of_data(i) <= Master_Data;
if i = 49 then
i <= 0;
else
i <= i + 1;
end if;
end if;
end if;
EDIT:
You can see that the flag is being asserted and the state changes here.
Further EDIT:
Consider making your state machine synchronous and removing the next_state signal. eg.
type state_t is (idle_s, send_s, others_s);
signal state : state_t := idle_s;
...
process(clk,rst)
begin
if rst = '1' then
-- rst
elsif rising_edge(clk) then
case (state) is
when idle_s =>
if flag = '1' then
state <= send_s;
else
state <= idle_s;
end if;
when send_s =>
-- Do stuff
when others =>
-- stuff
end case;
end if;
end process;
If you want to assign your outputs as soon as your state changes, you can use a two process state machine. One of the processes (synchronous) is used to control state transitions, the other is used to control the output (combinational). You would effectively have another process similar to the first:
process(state)
begin
case state is
when idle_s =>
my_output <= '0';
when send_s =>
-- Assign output as necessary
my_output <= '1';
when others =>
--assign output
end case;
end process;
An example is shown here.
module accumulator (
input [7:0] A ,
input reset,
input clk,
output reg carryout,
output reg overflow,
output reg [8:0] S,
output reg HEX0,
output reg HEX1,
output reg HEX2,
output reg HEX3
);
reg signA;
reg signS;
reg [7:0] magA;
reg [7:0] magS;
reg Alarger;
initial begin
S = 9'b000000000;
end
always_ff # (posedge clk, posedge reset) begin
if (reset) begin
S = 9'b000000000;
end
else begin
begin
signA <= A[7]; //Is A negative or positive
signS <= S[7];
S <= A + S;
end
if (signA == 1) begin //A is negative so magnitude is of 2s compliment
magA <= (~A[7:0] + 1'b1);
end
else begin
magA <= A;
end
if (signS == 1) begin //sum is negative so magnitude is of 2s compliment
magS <= (~S[7:0] + 1'b1);
end
else begin
magS <= S;
end
if (magA > magS) begin
Alarger <= 1'b1; //Magnitude of A is larger than magnitude of sum
end
else begin
Alarger <= 1'b0;
end
if ((signA == 1) & (Alarger == 1) & (S[7] == 0)) begin
overflow <= 1'b1;
end
else begin
overflow <= 1'b0;
end
if ((signS == 1) & (Alarger == 0) & (S[7] == 0)) begin
overflow <= 1'b1;
end
else begin
overflow <= 1'b0;
end
if ((signS == 1) & (signA == 1) & (S[7] == 0)) begin
overflow <= 1'b1;
end
else begin
overflow <= 1'b0;
end
if ((signS == 0) & (signA == 0) & (S[7] == 1)) begin
overflow <= 1'b1;
end
else begin
overflow <= 1'b0;
end
if (S[8] == 1) begin //carryout occurred
carryout <= 1'b1;
overflow <= 1'b0;
S <= 9'b000000000; //sum no longer valid
end
else begin
carryout <= 1'b0;
end
display_hex h1 //display of A
(
.bin (magA),
.hexl (HEX2),
.hexh (HEX3)
);
display_hex h2 //display of sum
(
.bin (S[7:0]),
.hexl (HEX0),
.hexh (HEX1)
);
end
end
endmodule
I am trying to make an accumulator that adds A (8 digit binary value that can be signed or unsigned) repeatedly to the sum. Once the sum is computed, then sum and A should display the value on 4 hex display LEDs (2 LEDs for A and 2 LEDs for sum). However, I am having a hard time getting it to compile. I have searched the error code and it seems like a general error for a syntax error and can have several meanings.
The error is the result of these two lines:
display_hex h1 //display of A
(
.bin (magA),
.hexl (HEX2),
.hexh (HEX3)
);
display_hex h2 //display of sum
(
.bin (S[7:0]),
.hexl (HEX0),
.hexh (HEX1)
);
Here, it appears you have a module named display_hex which converts an 8-bit value into the needed digits for a seven segment display. You are trying to use the module as if it were a function and modules are very much NOT functions. Modules in Verilog (or SystemVerilog as you are using, but the difference is really token at this point) can be though of as a group of hardware that takes in some inputs and spits out some outputs; and its important to note that they are static things. They either exist in the design or they do not; just like using ICs on a breadboard. The top module is the breadboard and the modules you declare under that module are components you are plugging into the board. The inputs and outputs are the various connections (pins) you must wire up to make everything work.
That said, always blocks (like the always_ff you are using) form a way of describing the logic and registers inside modules. Thus, you do thinks like assign logic/reg variables inside them to describe how the hardware behaves. If you look at your logic, you'll notice that the module declarations are dependent on reset; ie if reset is asserted, these modules wont exist, which doesnt make any sense. Electrical signals don't make entire ICs in a circuit disappear! Thus, you need to pull your module declaration out of your logical description of your acculumator, like so:
module accumulator (
...
);
...
display_hex h1 //display of A
(
.bin (magA),
.hexl (HEX2),
.hexh (HEX3)
);
display_hex h2 //display of sum
(
.bin (S[7:0]),
.hexl (HEX0),
.hexh (HEX1)
);
...
always_ff #(posedge clk, posedge reset) begin
// Your accumulator logic here
...
end
endmodule
Notice that the module declarations for the display_hex modules are stand alone, as I am declaring these modules exist, not dependence on anything!
However, there are a number of issues with your design besides that:
As you are using SystemVerilog constructs (always_ff), you should declare all of your variables type logic, not reg or left blank (ie, input clk should be input logic clk, reg signA should be logic signA). The logic type just makes everything easier, so use it :)
In your always_ff block, you do reset correctly except that the assignment should really be NBA (use S <= 9'b0;, not S = 9'b0; in the if (reset))
You use NBA inside your always_ff, which is correct, however, it appears you need to use these values right away in the following logic. This will not work as you expect, or at least it will not act within the same clock cycle. To fix this, youll need to decide what should be a register and what should just be values resulting from intermediate logic, then create a separate always_comb for the intermediate values.
I am making the assumption that the HEX variables are meant for seven segment displays, so they should probably declared at least [6:0] HEXn
I was not able to reproduce the exact error, but moving the instantiations of display_hex outside always_ff resolves the main issue:
module accumulator
(
/* ... */
);
// ...
always_ff # (posedge clk, posedge reset) begin
/* ... */
end
display_hex h1 (
/* ... */
);
display_hex h2 (
/* ... */
);
endmodule
Another thing: The code drives variable S from initial as well as always. This creates multiple drivers and the code will not compile. To fix this, remove the initial completely, you don't need it since S will be set to 0 when reset is asserted.
OR
You can move all the logic into the initial block; it'd look something like this (but this, most probably, won't synthesize):
initial begin
S = 0;
forever begin
wait #(posedge clock);
// Do stuff here ..
end
end
i'm beginner in verilog and digital circuits, and i have one doubt in the code below. In this code i made a state machine that saves values in a "reg" into another module in verilog. I made this code just to explain my doubt:
//STATE MACHINE
module RegTest(clk,enable,reset, readData1_out);
parameter State1 = 0;
parameter State2 = 1;
parameter State3 = 2;
parameter State4 = 3;
parameter State5 = 4;
parameter State6 = 5;
parameter State7 = 6;
parameter State8 = 7;
parameter State9 = 8;
parameter State10 = 9;
parameter Beg = 10;
input clk, enable, reset;
output readData1_out;
wire clk,enable, reset;
reg[5:0] State;
reg writeEn ;
reg [15:0] writeData;
wire [15:0] readData1;
wire writeEn_out = writeEn;
RegFile registrador_component (
.dataIn(writeData),
.dataOut(readData1),
.clock(clk),
.writeEnable(writeEn)
);
defparam
registrador_component.WIDTH = 16;
always #(posedge clk or posedge reset) begin
if (reset)
begin
State = Beg;
end else begin
case (State)
Beg:
begin
State = State1;
end
State1:
begin
writeEn = 1 ;
writeData = 10;
State = State2;
end
State2:
begin
writeEn = 0 ;
State = State3;
end
State3:
begin
writeEn = 1;
writeData = readData1 + 10;
State = State4;
end
State4:
begin
writeEn = 0 ;
State = State5;
end
State5:
begin
writeEn = 1 ;
writeData = readData1 + 10;
State = State6;
end
State6:
begin
writeEn = 0 ;
State = State7;
end
State7:
begin
writeEn = 1 ;
writeData = readData1 + 10;
State = State8;
end
State8:
begin
writeEn = 0 ;
State = State9;
end
endcase
end
end
endmodule
//Example of a register file
module RegFile(clock, writeEnable, dataIn, dataOut);
parameter WIDTH = 16;
input clock, writeEnable;
input [WIDTH-1 : 0] dataIn;
output [WIDTH-1 : 0] dataOut;
wire [WIDTH-1 : 0] dataOut;
reg [WIDTH-1 : 0] wha;
assign dataOut = wha;
always#( posedge clock)
begin
if (writeEnable)
wha = dataIn;
end
endmodule
My doubt is, why do I need to wait 1 cycle to get the value that is stored in RegFile?
Why can't I skip the State2 for example?
You do in fact have 2 clock cycles of delay in the code you wrote above. It would help if you simulated this so you can see it for yourself, but I'll describe it.
On the first cycle, WriteEnable goes high. It takes 1 full clock cycle to be valid to other parts of the logic. So after the first clock cycle is done, WriteEnable will be available for use elsewhere.
On the second cycle, your regFile module can "see" the fact that WriteEnable went high previously. It then will put dataIn into wha signal, which gets passed to dataOut. So after the second clock cycle is done, dataOut will be available for use elsewhere. (It gets used on the third clock cycle in State 3).
This is why you need to go to state 2. State 2 allows for the 1 extra clock cycle needed for RegFile to register the output data.
Clock cycle delay is an extremely important concept to understand, so it's good that you're putting in the time when you are still new to fully grasp it.
For more information see this tutorial here, it explains registers and clock cycle delay and will be useful for you.
Clock Cycle Delays and Registered Logic
I seem to have some issues anytime I try anything with I/O for verilog. Modelsim either throws function not supported for certain functions or does nothing at all. I simply need to read a file character by character and send each bit through the port. Can anyone assist
module readFile(clk,reset,dEnable,dataOut,done);
parameter size = 4;
//to Comply with S-block rules which is a 4x4 array will multiply by
// size so row is the number of size bits wide
parameter bits = 8*size;
input clk,reset,dEnable;
output dataOut,done;
wire [1:0] dEnable;
reg dataOut,done;
reg [7:0] addr;
integer file;
reg [31:0] c;
reg eof;
always#(posedge clk)
begin
if(file == 0 && dEnable == 2'b10)begin
file = $fopen("test.kyle");
end
end
always#(posedge clk) begin
if(addr>=32 || done==1'b1)begin
c <= $fgetc(file);
// c <= $getc();
eof <= $feof(file);
addr <= 0;
end
end
always#(posedge clk)
begin
if(dEnable == 2'b10)begin
if($feof(file))
done <= 1'b1;
else
addr <= addr+1;
end
end
//done this way because blocking statements should not really be used
always#(addr)
begin:Access_Data
if(reset == 1'b0) begin
dataOut <= 1'bx;
file <= 0;
end
else if(addr<32)
dataOut <= c[31-addr];
end
endmodule
I would suggest reading the entire file at one time into an array, and then iterate over the array to output the values.
Here is a snippet of how to read bytes from a file into a SystemVerilog queue. If you need to stick to plain old Verilog you can do the same thing with a regular array.
reg [8:0] c;
byte q[$];
int i;
// Read file a char at a time
file = $fopen("filename", "r");
c = $fgetc(file);
while (c != 'h1ff) begin
q.push_back(c);
$display("Got char [%0d] 0x%0h", i++, c);
c = $fgetc(file);
end
Note that c is defined as a 9-bit reg. The reason for is that $fgetc will return -1 when it reaches the end of the file. In order to differentiate between EOF and a valid 0xFF you need this extra bit.
I'm not familiar with $feof and don't see it in the Verilog 2001 spec, so that may be something specific to Modelsim. Or it could be the source of the "function not supported."