def make_packet(payload, samples_per_symbol, bits_per_symbol,
preamble, access_code,
pad_for_usrp=True, do_whitening=False, add_crc=False):
"""
Build a packet
Args:
payload: packet payload, len [0, 4096]
samples_per_symbol: samples per symbol (needed for padding calculation) (int)
bits_per_symbol: (needed for padding calculation) (int)
preamble: (eg: 10101010...)
access_code: the sync word
pad_for_usrp:
do_whitening: ccxxxx whitening version
add_crc: add CRC16 (2 bytes) checksum
Packet will have access code at the beginning, followed by length (1 byte), payload
and finally CRC-16.
"""
if not packet_utils.is_1_0_string(preamble):
raise ValueError, "preamble must be a string containing only 0's and 1's (%r)" % (preamble,)
if not packet_utils.is_1_0_string(access_code):
raise ValueError, "access_code must be a string containing only 0's and 1's (%r)" % (access_code,)
(packed_access_code, padded) = packet_utils.conv_1_0_string_to_packed_binary_string(access_code)
(packed_preamble, ignore) = packet_utils.conv_1_0_string_to_packed_binary_string(preamble)
# len
payload_length = len(payload)
# header (1 byte)
pkt_hd = make_header(payload_length)
# data
pkt_dt = payload
# final message
final_message = ''.join((pkt_hd, pkt_dt))
# CRC ?
if add_crc:
crc = crc16(final_message)
#print "crc: %02x %02x" % (ord(crc[0:1]), ord(crc[1:2]))
final_message = ''.join((final_message, crc))
# Whitening ?
pkt = ''
if do_whitening:
pkt = ''.join((packed_preamble, packed_access_code, whiten(final_message), '\x55'))
else:
pkt = ''.join((packed_preamble, packed_access_code, final_message, '\x55'))
# Padding ?
if pad_for_usrp:
usrp_packing = packet_utils._npadding_bytes(len(pkt), samples_per_symbol, bits_per_symbol) * '\x55'
pkt = pkt + usrp_packing
return pkt
def make_packet(payload, samples_per_symbol, bits_per_symbol, pad_for_usrp=True): """ Build a packet Args: payload: packet payload, len [0, 4096] samples_per_symbol: samples per symbol (needed for padding calculation) (int) bits_per_symbol: (needed for padding calculation) (int) pad_for_usrp: Packet will have the preamble and access code at the beginning, followed by the encoded payload and an 8-bit CRC. """ # CRC crc = crc8(payload) raw_message = ''.join((payload, crc)) # 4b/6b encoding encoded_nibbles = [] for element in raw_message: for shift in [4, 0]: encoded_nibble = ENCODER_TABLE[(ord(element) >> shift) & 0xf] encoded_nibbles.append(encoded_nibble) # Nibble to bit conversion bits = [] for element in encoded_nibbles: for bit_index in range(0, 6)[::-1]: bit = (element >> bit_index) & 0x01 bits.append(bit) # Bit padding if len(bits) % 8: padding = [0, 1] * ((len(bits) % 8) / 2) bits.extend(padding) # Convert the bits to bytes encoded_message = str(bits_to_bytes(bits)) # Prepend the preamble and sync words/access code to the message packet = ''.join((PREAMBLE, ACCESS_CODE, encoded_message, PADDING)) # Padding (optional) if pad_for_usrp: usrp_packing = packet_utils._npadding_bytes(len(packet), samples_per_symbol, bits_per_symbol) * '\x00' packet = packet + usrp_packing return packet
