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#!/usr/bin/env python3 | ||
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# Copyright (c) 2014 Guy Hutchison | ||
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# Redistribution and use in source and binary forms, with or without modification, | ||
# are permitted provided that the following conditions are met: | ||
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# 1. Redistributions of source code must retain the above copyright notice, this | ||
# list of conditions and the following disclaimer. | ||
# 2. Redistributions in binary form must reproduce the above copyright notice, | ||
# this list of conditions and the following disclaimer in the documentation | ||
# and/or other materials provided with the distribution. | ||
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND | ||
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED | ||
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE | ||
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR | ||
# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES | ||
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; | ||
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON | ||
# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | ||
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS | ||
# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | ||
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import migen | ||
import operator | ||
from migen.fhdl.std import * | ||
from migen.fhdl.verilog import convert | ||
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# Join two lists a and b, such that redundant terms are removed | ||
def join_lists(a, b): | ||
z = [] | ||
for x in a+b: | ||
if x not in z: | ||
z.append(x) | ||
else: | ||
z.remove(x) | ||
return z | ||
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def join_operator(list, op): | ||
if len(list) == 0: | ||
return [] | ||
elif len(list) == 1: | ||
return list[0] | ||
elif len(list) == 2: | ||
return op(list[0], list[1]) | ||
else: | ||
return op(list[0], join_operator(list[1:], op)) | ||
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def calc_code_bits(data_bits): | ||
m = 1 | ||
c = 0 | ||
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while c < data_bits: | ||
m += 1 | ||
c = 2**m - m - 1 | ||
return m | ||
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# build_seq() is used to create the selection of bits which need | ||
# to be checked for a particular data parity bit. | ||
def build_seq(bnum, out_width): | ||
tmp = [] | ||
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ptr = 0 | ||
cur = 0 | ||
skip = 2**bnum-1 | ||
if skip == 0: | ||
check = 2**bnum | ||
else: | ||
check = 0 | ||
while cur < out_width: | ||
if check > 0: | ||
if (cur != 2**bnum-1): | ||
tmp.append(cur) | ||
ptr += 1 | ||
check -= 1 | ||
if check == 0: | ||
skip = 2**bnum | ||
else: | ||
skip -= 1 | ||
if skip == 0: | ||
check = 2**bnum | ||
cur += 1 | ||
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return tmp | ||
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# build_bits() is used for the generator portion, it combines the | ||
# bit sequences for all input and parity bits which are used and | ||
# removes redundant terms. | ||
def build_bits(in_width, gen_parity=True): | ||
pnum = 1 | ||
innum = 0 | ||
blist = [] | ||
num_code_bits = calc_code_bits(in_width) | ||
out_width = in_width + num_code_bits | ||
v = [list()] * out_width | ||
code_bit_list = [] | ||
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for b in range(out_width): | ||
if (b+1) == pnum: | ||
pnum = 2*pnum | ||
else: | ||
v[b] = [innum] | ||
innum += 1 | ||
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for b in range(num_code_bits): | ||
vindex = 2**b-1 | ||
blist = build_seq(b, out_width) | ||
for bli in blist: | ||
v[vindex] = join_lists(v[vindex], v[bli]) | ||
code_bit_list.append(v[vindex]) | ||
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# Calculate parity bit | ||
if gen_parity: | ||
pbit = [] | ||
for b in v: | ||
pbit = join_lists(pbit, b) | ||
code_bit_list.append(pbit) | ||
return code_bit_list | ||
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# xor_tree() takes a signal and a list of bits to be applied from | ||
# the signal and generates a balanced xor tree as output. | ||
def xor_tree(in_signal, in_bits): | ||
if len(in_bits) == 0: | ||
print ("ERROR: in_bits must be > 0") | ||
elif len(in_bits) == 1: | ||
return in_signal[in_bits[0]] | ||
elif len(in_bits) == 2: | ||
return in_signal[in_bits[0]] ^ in_signal[in_bits[1]] | ||
elif len(in_bits) == 3: | ||
return in_signal[in_bits[0]] ^ in_signal[in_bits[1]] ^ in_signal[in_bits[2]] | ||
else: | ||
split = int(len(in_bits)/2) | ||
return xor_tree(in_signal, in_bits[0:split]) ^ xor_tree(in_signal, in_bits[split:]) | ||
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# Base class for Hamming code generator/checker. | ||
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# Hamming code generator class | ||
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# The class constructor takes a single required input, which is the number of | ||
# bits of the input data. The module creates a single output, which is a set | ||
# of code check bits and a parity bit. | ||
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# This generator and its corresponding checker will only generate a single- | ||
# error correct, double-error detect code. If double-error detection is | ||
# not desired, the most-significant code_out bit can be left unconnected. | ||
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# If generated as a top-level module, contains its suggested module name | ||
# in self.name and list of ports in self.ports | ||
class HammingGenerator(Module): | ||
def __init__(self, input_size): | ||
self.input_size = input_size | ||
self.data_in = Signal(input_size) | ||
self.code_out = Signal(calc_code_bits(input_size)+1) | ||
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xor_bits = build_bits(self.input_size) | ||
for b in range(len(xor_bits)): | ||
self.comb += self.code_out[b].eq(xor_tree(self.data_in, xor_bits[b])) | ||
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# Hamming code checker class | ||
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# Constructor takes two parameters: | ||
# input_size (bits of data bus, not counting check bits) | ||
# correct (boolean, True if output data should be corrected) | ||
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# If used as a check/correct module, the module creates an | ||
# enable input which can dynamically turn off error correction | ||
# for debug. | ||
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# If double-bit detection is not desired, the most-significant | ||
# code_in bit can be tied to 0, and the dberr output port left | ||
# unconnected. | ||
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# If generated as a top-level module, contains its suggested module name | ||
# in self.name and list of ports in self.ports | ||
class HammingChecker(Module): | ||
def __init__(self, input_size, correct=True, gen_parity=True): | ||
self.input_size = input_size | ||
self.correct = correct | ||
self.data_in = Signal(input_size) | ||
self.code_bits = calc_code_bits(input_size) | ||
self.code_in = Signal(self.code_bits+1) | ||
self.code_out = Signal(self.code_bits) | ||
self.sberr = Signal() | ||
if gen_parity: | ||
self.dberr = Signal() | ||
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# vector of which interleaved bit position represents a particular | ||
# data bit, used for error correction | ||
dbits = [] | ||
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# Create interleaved vector of code bits and data bits with code bits | ||
# in power-of-two positions | ||
pnum = 0 | ||
dnum = 0 | ||
self.par_vec = Signal(input_size+self.code_bits) | ||
for b in range(input_size+calc_code_bits(input_size)): | ||
if b+1 == 2**pnum: | ||
self.comb += self.par_vec[b].eq(self.code_in[pnum]) | ||
pnum += 1 | ||
else: | ||
self.comb += self.par_vec[b].eq(self.data_in[dnum]) | ||
dbits.append(b) | ||
dnum += 1 | ||
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if correct: | ||
self.enable = Signal() | ||
self.correct_out = Signal(input_size) | ||
self.data_out = Signal(input_size, name='data_out') | ||
for b in range(input_size): | ||
self.comb += self.correct_out[b].eq((self.code_out == (dbits[b]+1)) ^ self.data_in[b]) | ||
self.comb += If(self.enable, self.data_out.eq(self.correct_out)).Else(self.data_out.eq(self.data_in)) | ||
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self.comb += self.sberr.eq(self.code_out != 0) | ||
if gen_parity: | ||
parity = Signal() | ||
self.comb += parity.eq(xor_tree(self.data_in, range(input_size)) ^ xor_tree(self.code_in, range(self.code_bits+1))) | ||
self.comb += self.dberr.eq(~parity) | ||
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for b in range(calc_code_bits(self.input_size)): | ||
bits = [2**b-1] | ||
bits += build_seq(b, self.input_size+calc_code_bits(self.input_size)) | ||
self.comb += self.code_out[b].eq(xor_tree(self.par_vec, bits)) |