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tribits_to_integer, fixed trellis_3_4_decode 

git-svn-id: http://op25.osmocom.org/svn/trunk@32 65a5c917-d112-43f1-993d-58c26a4786be
This commit is contained in:
mossmann 2008-04-16 07:54:38 +00:00
parent 2d0030dde8
commit a096f35022
1 changed files with 17 additions and 9 deletions
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26
python/c4fm-decode.py
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@ -52,6 +52,14 @@ def dibits_to_integer(dibits):
integer += dibit
return integer
# return integer represented by sequence of tribits
def tribits_to_integer(tribits):
integer = 0
for tribit in tribits:
integer = integer << 3
integer += tribit
return integer
# extract a block of symbols from in between status symbols
# return extracted block, list of status symbols, and number of symbols consumed
def extract_block(symbols, length, index):
@ -103,7 +111,7 @@ def trellis_1_2_decode(input):
# TODO: exception handling: at least try the next best match
state = similarity.index(4)
output.append(state)
return output
return output[:48]
# 3/4 rate trellis decode a sequence of symbols
# TODO: Use soft symbols instead of hard symbols.
@ -135,8 +143,7 @@ def trellis_3_4_decode(input):
# TODO: exception handling: at least try the next best match
state = similarity.index(4)
output.append(state)
# TODO: Broken! returns list of tribits, but list of dibits expected
return output
return tribits_to_integer(output[:48])
# fake (64,16,23) BCH decoder, no error correction
# spec sometimes refers to this as (63,16,23) plus a parity bit
@ -336,7 +343,7 @@ def decode_frame(symbols):
tsbk = trellis_1_2_decode(data_deinterleave(tsbk_symbols))
# TODO: verify with CRC
# TODO: see 102.AABC-B for further decoding
print "TSBK: 0x%025x" % (dibits_to_integer(tsbk))
print "TSBK: 0x%024x" % (dibits_to_integer(tsbk))
last_block_flag = tsbk[0] >> 1
elif data_unit_id == 12:
print "Found a Packet Data Unit"
@ -385,14 +392,15 @@ def decode_frame(symbols):
status_symbols.extend(block_status_symbols)
consumed += block_consumed
data_block = trellis_3_4_decode(data_deinterleave(data_block_symbols))
# data_block is 144 bits
# Data Block Serial Number, 7 bits
data_block_serial_number = data_block[:4] & 0xFE
data_block_serial_number = (data_block >> 128) & 0xFE00
# CRC-9, 9 bits
data_block_crc = data_block[3:8] & 0x1FF
data_block_crc = (data_block >> 128) & 0x01FF
#TODO: verify data block CRC
user_data.extend(data_block[8:72])
packet_crc = user_data[-16:]
user_data = user_data[:-16]
user_data.extend(data_block & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF)
packet_crc = user_data & 0xFFFFFFFF
user_data = user_data >> 32
#TODO: verify packet CRC
elif format == 0x3:
print "PDU is a Response Packet"