Examples and discussion about CRC implementation

[sree205]

Hi,
would it be possible to calculate CRC for incoming data which is not a byte-multiple? lets say 10 or 15 or 26 or any such random no. ?

i came across another crc implementation post which uses this following polynomial.

g(x) = x12+x10+x8+x5+x4+x3+1

in this explanation, there is also something like a seed value given. is this what the input data should be ?

 

[throwaway18]

CRC implementation

would it be possible to calculate CRC for incoming data which is not a byte-multiple?/quote]

The usuall method is to pad the data with zero's.

 

[sree205]

CRC implementation

another question. for a polynomial of degree 12, shouldn't we get a checksum of 13 bits (coz, x^0, 1 is also taken into account) ?

 

[xqiang]

Re: CRC implementation

Maybe the attachement will help you.

 

[sree205]

Re: CRC implementation

Hi,
I have attached the CRC rtl from verilog designer's library. it has been implemented as a simple LFSR would be. On testing it with the testbench, i find that the checksum obtained with this is not the same as CRC should be. so, why is there a disparity ?

this link provides a 8-bit crc calculator using a polynomial x^8+x^2+x+1. feel free to check the crc values.

http://www.smbus.org/faq/crc8Applet.htm

 

[m.abdulmoniem]

Re: CRC implementation

Hi everybody
I'm searching for a dependable Crc32 calculator to verify my work

Could anybody help me?

Thanks
Mohammad

 

[m.abdulmoniem]

Re: CRC implementation

Hi
My code implements the parallel crc32 where the data width is a nibble (4 bits) which is applied for ethernet

Now, I made a testbench that examines the value of the generated CRC and counts the number of clocks required to get it

It examines the value of the CRC by comparing it with a value I obtained by the calculator from http://www.zorc.breitbandkatze.de/crc.html

for example:
using this calculator for a Data message=U (which is 8'h55) we will get CRC=C9034AF6

to check my work I made this testbench
// eb1 1
always @(posedge Clk)
begin
Data = 4'b0101;
if (Crc[31:0] == 32'hc9034af6) begin
$display("the CRC is given after", Clk_Counter," clocks");
#5 $finish;
end
end

when running the simulator and make a break point at the $display line I found it doesn't stop and continue running forever

Do you think there is a mistake with my work?
Do you think the result of this calculator is not right?

I appreciate ur help

Thanks

 

[m.abdulmoniem]

Re: CRC implementation

Also, I want to add something
The tested core compares the Crc value with the magic number of 32'hc704dd7b by this line
assign CrcError = Crc[31:0] != 32'hc704dd7b;

and when I tried to simulate it I found the CrcError signal is always high

I don't know where is the mistake?

could you help please?