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Compute ECC for 2k pages and try correcting single-bit errors #35

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eeafcc2
flashimage: remove unnecessary ord()
osresearch Mar 12, 2022
be19f08
check_ecc: handle both 512 and 2048 byte block size ecc
osresearch Mar 17, 2022
725b386
ecc: use an array in ecc2, output bitcount
osresearch Mar 17, 2022
a9fb764
ecc: attempt to correct errors
osresearch Mar 17, 2022
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122 changes: 40 additions & 82 deletions dumpflash/ecc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ def calc(self, body):
p4 = 0
p4_ = 0
for i in range(0, len(body), 1):
ch = ord(body[i])
ch = body[i]
bit0 = ch & 0x1
bit1 = (ch >> 1) & 0x1
bit2 = (ch >> 2) & 0x1
Expand Down Expand Up @@ -115,90 +115,48 @@ def calc(self, body):

def calc2(self, body):
par = 0
rp0 = 0
rp1 = 0
rp2 = 0
rp3 = 0
rp4 = 0
rp5 = 0
rp6 = 0
rp7 = 0
rp8 = 0
rp9 = 0
rp10 = 0
rp11 = 0
rp12 = 0
rp13 = 0
rp14 = 0
rp15 = 0
rp = [0] * 18

for i in range(0, len(body), 1):
cur = ord(body[i])
cur = body[i]
par ^= cur

if i & 0x01:
rp1 ^= cur
else:
rp0 ^= cur
if i & 0x02:
rp3 ^= cur
else:
rp2 ^= cur
if i & 0x04:
rp5 ^= cur
else:
rp4 ^= cur
if i & 0x08:
rp7 ^= cur
else:
rp6 ^= cur
if i & 0x10:
rp9 ^= cur
else:
rp8 ^= cur
if i & 0x20:
rp11 ^= cur
else:
rp10 ^= cur
if i & 0x40:
rp13 ^= cur
else:
rp12 ^= cur
if i & 0x80:
rp15 ^= cur
else:
rp14 ^= cur

code0 = \
(self.Parity[rp7] << 7)| \
(self.Parity[rp6] << 6)| \
(self.Parity[rp5] << 5)| \
(self.Parity[rp4] << 4)| \
(self.Parity[rp3] << 3)| \
(self.Parity[rp2] << 2)| \
(self.Parity[rp1] << 1)| \
(self.Parity[rp0] << 0)

code1 = \
(self.Parity[rp15] << 7)| \
(self.Parity[rp14] << 6)| \
(self.Parity[rp13] << 5)| \
(self.Parity[rp12] << 4)| \
(self.Parity[rp11] << 3)| \
(self.Parity[rp10] << 2)| \
(self.Parity[rp9] << 1)| \
(self.Parity[rp8] << 0)

code2 = \
(self.Parity[par & 0xf0] << 7) | \
(self.Parity[par & 0x0f] << 6) | \
(self.Parity[par & 0xcc] << 5) | \
(self.Parity[par & 0x33] << 4) | \
(self.Parity[par & 0xaa] << 3) | \
(self.Parity[par & 0x55] << 2)

code0 = ~code0
code1 = ~code1
code2 = ~code2
# compute the row parities by testing
# the r^th bit of the address i
for r in range(0,9):
if (i >> r) & 1:
rp[2*r + 1] ^= cur
else:
rp[2*r + 0] ^= cur

code0 = 0
code1 = 0

for i in range(0,8):
code0 |= self.Parity[rp[i+0]] << i
code1 |= self.Parity[rp[i+8]] << i

# column parities
cp5 = par & 0b11110000
cp4 = par & 0b00001111
cp3 = par & 0b11001100
cp2 = par & 0b00110011
cp1 = par & 0b10101010
cp0 = par & 0b01010101

# 512-byte blocks squeeze the extra row parities into code2
code2 = 0 \
| (self.Parity[cp5] << 7) \
| (self.Parity[cp4] << 6) \
| (self.Parity[cp3] << 5) \
| (self.Parity[cp2] << 4) \
| (self.Parity[cp1] << 3) \
| (self.Parity[cp0] << 2) \
| (self.Parity[rp[17]] << 1) \
| (self.Parity[rp[16]] << 0)

code0 ^= 0xFF
code1 ^= 0xFF
code2 ^= 0xFF

return (code0, code1, code2)
126 changes: 99 additions & 27 deletions dumpflash/flashimage.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,89 @@ def set_use_ansi(self, use_ansi):
self.UseAnsi = use_ansi
self.SrcImage.set_use_ansi(use_ansi)

def bitcount(self, x):
count = 0
while x != 0:
count += x & 1
x >>= 1
return count

def check_ecc_page_512(self, page, subpage, body, oob_ecc0, oob_ecc1, oob_ecc2):
if (oob_ecc0 == 0xff and oob_ecc1 == 0xff and oob_ecc2 == 0xff) \
or (oob_ecc0 == 0x00 and oob_ecc1 == 0x00 and oob_ecc2 == 0x00):
return True

(ecc0, ecc1, ecc2) = ecc.Calculator().calc2(body)

ecc0_xor = ecc0 ^ oob_ecc0
ecc1_xor = ecc1 ^ oob_ecc1
ecc2_xor = ecc2 ^ oob_ecc2

if ecc0_xor == 0 and ecc1_xor == 0 and ecc2_xor == 0:
return True

bits = self.bitcount(ecc0_xor) + self.bitcount(ecc1_xor) + self.bitcount(ecc2_xor)
bad_byte = -1
bad_bit = 0
corrected = "Error"

if bits == 12:
# column parity bits 5, 3, and 1 determine which bit is bad
cp5 = (ecc2_xor >> 7) & 1
cp3 = (ecc2_xor >> 5) & 1
cp1 = (ecc2_xor >> 3) & 1
bad_bit = 0 \
| cp5 << 2 \
| cp3 << 1 \
| cp1 << 0

# row parities bits 17, 15, 13, ... 1 determine which byte is bad
rp17 = (ecc2_xor >> 1) & 1
rp15 = (ecc1_xor >> 7) & 1
rp13 = (ecc1_xor >> 5) & 1
rp11 = (ecc1_xor >> 3) & 1
rp9 = (ecc1_xor >> 1) & 1
rp7 = (ecc0_xor >> 7) & 1
rp5 = (ecc0_xor >> 5) & 1
rp3 = (ecc0_xor >> 3) & 1
rp1 = (ecc0_xor >> 1) & 1
bad_byte = 0 \
| rp17 << 8 \
| rp15 << 7 \
| rp13 << 6 \
| rp11 << 5 \
| rp9 << 4 \
| rp7 << 3 \
| rp5 << 2 \
| rp3 << 1 \
| rp1 << 0

# try flipping that bit and re-computing
new_body = bytearray(body)
new_body[bad_byte] ^= 1 << bad_bit
(ecc0_new, ecc1_new, ecc2_new) = ecc.Calculator().calc2(new_body)

ecc0_xor2 = ecc0_new ^ oob_ecc0
ecc1_xor2 = ecc1_new ^ oob_ecc1
ecc2_xor2 = ecc2_new ^ oob_ecc2

if ecc0_xor2 == 0 and ecc1_xor2 == 0 and ecc2_xor2 == 0:
corrected = "Corrected"

# page_in_block = page%self.SrcImage.PagePerBlock

offset = self.SrcImage.get_page_offset(page)
block = page/self.SrcImage.PagePerBlock

#print('ECC Error (Block: %3d Page: %3d Data Offset: 0x%x OOB Offset: 0x%x)' % (block, page, offset, offset+self.SrcImage.PageSize))
print('ECC %s (Block: %3d Page: %3d.%d Data Offset: 0x%x)' % (corrected, block, page, subpage, offset))
print(' OOB: 0x%.2x 0x%.2x 0x%.2x' % (oob_ecc0, oob_ecc1, oob_ecc2))
print(' Calc: 0x%.2x 0x%.2x 0x%.2x' % (ecc0, ecc1, ecc2))
print(' XOR: 0x%.2x 0x%.2x 0x%.2x bitcount %d byte %x.%d' % (ecc0_xor, ecc1_xor, ecc2_xor, bits, bad_byte, bad_bit))
print('')

return False

def check_ecc(self, start_page = 0, end_page = -1):
block = 0
count = 0
Expand All @@ -43,7 +126,6 @@ def check_ecc(self, start_page = 0, end_page = -1):
if end_page%self.SrcImage.PagePerBlock > 0:
end_block += 1

ecc_calculator = ecc.Calculator()
start = time.time()
for page in range(0, self.SrcImage.PageCount, 1):
block = page/self.SrcImage.PagePerBlock
Expand All @@ -69,32 +151,22 @@ def check_ecc(self, start_page = 0, end_page = -1):
break

count += 1
body = data[0:self.SrcImage.PageSize]
oob_ecc0 = ord(data[self.SrcImage.PageSize])
oob_ecc1 = ord(data[self.SrcImage.PageSize+1])
oob_ecc2 = ord(data[self.SrcImage.PageSize+2])

if (oob_ecc0 == 0xff and oob_ecc1 == 0xff and oob_ecc2 == 0xff) or (oob_ecc0 == 0x00 and oob_ecc1 == 0x00 and oob_ecc2 == 0x00):
continue

(ecc0, ecc1, ecc2) = ecc_calculator.calc(body)

ecc0_xor = ecc0 ^ oob_ecc0
ecc1_xor = ecc1 ^ oob_ecc1
ecc2_xor = ecc2 ^ oob_ecc2

if ecc0_xor != 0 or ecc1_xor != 0 or ecc2_xor != 0:
error_count += 1

# page_in_block = page%self.SrcImage.PagePerBlock

offset = self.SrcImage.get_page_offset(page)
print('ECC Error (Block: %3d Page: %3d Data Offset: 0x%x OOB Offset: 0x%x)' % (block, page, offset, offset+self.SrcImage.PageSize))
print(' OOB: 0x%.2x 0x%.2x 0x%.2x' % (oob_ecc0, oob_ecc1, oob_ecc2))
print(' Calc: 0x%.2x 0x%.2x 0x%.2x' % (ecc0, ecc1, ecc2))
print(' XOR: 0x%.2x 0x%.2x 0x%.2x' % (ecc0 ^ oob_ecc0, ecc1 ^ oob_ecc1, ecc2 ^ oob_ecc2))
print('')

#body = data[0:self.SrcImage.PageSize]

if self.SrcImage.PageSize == 512:
if not self.check_ecc_page_512(page, 0, data[0:512], data[512+0], data[512+1], data[512+2]):
error_count += 1
elif self.SrcImage.PageSize == 2048:
# four 512 byte sub pages
for i in range(0,3):
if not self.check_ecc_page_512(
page, i,
data[i*512:i*512 + 512],
data[2048 + i*16 + 8],
data[2048 + i*16 + 9],
data[2048 + i*16 + 10],
):
error_count += 1
print('Checked %d ECC record and found %d errors' % (count, error_count))

def check_bad_block_page(self, oob):
Expand Down