Subversion Repositories fade_ether_protocol

#!/usr/bin/python

# This is the public domain code written by Wojciech M. Zabolotny

# ( wzab(at)ise.pw.edu.pl )

# The functionality has been inspired by the CRC Tool available

# at http://www.easics.com/webtools/crctool , however the code

# has been written independently.

# In fact I have decided to write this code, when I was not able to

# generate CRC with the crctool for a particular non-typical length

# of data word.

# The program crc_gen.py generates the VHDL code for CRC update for given

# length of the data vector.

# The length of the CRC results from the coefficient of the CRC polynomial.

# The arguments are as follows:

# 1st: Function name. The package name is created by prefixing it with

#        pkg_

# 2nd: L - for data fed LSB first, M for data fed MSB first

# 3rd: the width of the data bus,

# 4th and next: the coefficients of the polynomial (the exponents in fact).

# For example, to generate the expression for CRC7 for 12bit data transmitted LSB first

# you should call:

# crc_gen.py crc7_d12 L 12 7 3 0

# To generate CRC-12 for 16 bit data transmitted MSB first, you should call:

# crc_gen.py crc12_d16 M 16 12 11 3 2 1 0

# The generated code implements a package with the function calculating

# the new value of the CRC from the previous value of the CRC and

# the data word.

import sys

fun_name=sys.argv[1]

pkg_name = "pkg_"+fun_name

data_order=sys.argv[2]

if data_order != 'L' and data_order != 'M':

    print "The second argument must be 'L' or 'M', not the '"+data_order+"'"

    sys.exit(1)

data_len=int(sys.argv[3])

poly=[]

for i in range(4,len(sys.argv)):

    poly.append(int(sys.argv[i]))

crc_len=max(poly)

#The class "xor_result" implements result of xor-ing of multiple

# CRC and DATA bits

# dirty trick: the class relies on global variables crc_len and data_len

class xor_result:

    def __init__(self,c=-1,d=-1):

        self.c=crc_len*[0]

        self.d=data_len*[0]

        if(c>-1):

            self.c[c]=1

        if(d>-1):

            self.d[d]=1

    def copy(self):

        res=xor_result()

        for i in range(0,crc_len):

            res.c[i]=self.c[i]

        for i in range(0,data_len):

            res.d[i]=self.d[i]

        return res

    # The new XOR operator

    def __xor__(self,x):

        res=xor_result()

        for i in range(0,crc_len):

            res.c[i]=self.c[i]^x.c[i]

        for i in range(0,data_len):

            res.d[i]=self.d[i]^x.d[i]

        return res

    def tostr(self):

        res=""

        for i in range(0,crc_len):

            if self.c[i]==1:

                if res=="":

                    res+="c("+str(i)+")"

                else:

                    res+=" xor c("+str(i)+")"

        for i in range(0,data_len):

            if self.d[i]==1:

                if res=="":

                    res+="d("+str(i)+")"

                else:

                    res+=" xor d("+str(i)+")"

        return res

#Now we create the CRC vector, which initially contains only the bits

#of the initial value of the CRC

CRC=[ xor_result(c=i) for i in range(0,crc_len) ]

#And the data vector

DATA=[ xor_result(d=i) for i in range(0,data_len) ]

#Now we pass the data through the CRC polynomial

if data_order == 'L':

    d_range = range(0,data_len)

    ord_name = "LSB"

elif data_order == 'M':

    d_range = range(data_len-1,-1,-1)

    ord_name = "MSB"

else:

    print "Internal error"

    sys.exit(1)

for i in d_range:

    #We create the vector for the new CRC

    NCRC = [ xor_result() for k in range(0,crc_len) ]

    #First - the basic shift operation

    for j in range(1,crc_len):

        NCRC[j]=CRC[j-1].copy()

    #Now we add the feedback

    FB=DATA[i] ^ CRC[crc_len-1]

    for j in poly:

        if j == crc_len:

            # This does not require any action

            pass

        else:

            NCRC[j]=NCRC[j] ^ FB

    CRC=NCRC

pkg_text = '''library ieee;

use ieee.std_logic_1164.all;

package ''' + pkg_name +" is\n"

pkg_text += "  -- CRC update for "+str(crc_len)+"-bit CRC and "+\

    str(data_len)+"-bit data ("+ord_name+" first)\n"

pkg_text += "  -- The CRC polynomial exponents: "+str(poly)+"\n"

fun_decl = '  function ' + fun_name +"(\n" +\

'   din : std_logic_vector('+str(data_len-1)+' downto 0);\n'+\

'   crc : std_logic_vector('+str(crc_len-1)+' downto 0))\n'+\

'  return std_logic_vector'

pkg_text += fun_decl+';\n'

pkg_text += 'end '+pkg_name+';\n\n'

pkg_text +=  "package body " + pkg_name +" is\n"

pkg_text += fun_decl + ' is \n'

pkg_text += '    variable c,n : std_logic_vector(' + str(crc_len-1)+' downto 0);\n'

pkg_text += '    variable d : std_logic_vector(' + str(data_len-1)+' downto 0);\n'

pkg_text += '  begin\n'

pkg_text += '    c := crc;\n    d := din; \n'

for i in range(0,len(CRC)):

    pkg_text += "      n("+str(i)+") := "+CRC[i].tostr()+";\n"

pkg_text += '    return n;\n'

pkg_text += '  end '+fun_name+";\n"

pkg_text += 'end '+pkg_name+";\n"

print pkg_text