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xbee_api.py
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#!/usr/bin/python
import logging
import serial
logger = logging.getLogger('default')
# Sample packet:
# 7e 0 e 83 56 78 3f 0 1 7 0 1 0 3 ff 3 ff 62
#
# I/O data packet
#
# header:
#
# Total number of samples | na A5 A4 A3 A2 A1 A0 D8 | D7 D6 D5 D4 D3 D2 D1 D0 |
#
# sample data follows the header:
#
# DIO line data first (if enabled) | ADC line data
# x x x x x x x 8 | 7 6 5 4 3 2 1 0 | ADCn MSB | ADCn LSB
# in the example above:
#
# cmd -- 83 (16 bit I/O)
# 56 78 -- address
# 3f -- RSSI
# 0 -- options
# next follows I/O data packet (because cmd was 83)
# 1 -- num. of samples
# 7 -- first byte of channel spec, A1=1 A0=1 D8=1
# 0 -- second byte of channel spec, all other channels are off
# 1 -- first sample byte, D8=1 -- only if any of D channels enabled
# 0 -- second sample byte -- only if any of D channels enabled
# 3 -- ADC0 MSB
# ff -- ADC0 LSB
# 3 -- ADC1 MSB
# ff -- ADC1 LSB
class SerialIOPacket(object):
def __init__(self):
self.api_16_bit_adc = 0x83
self.api_64_bit_adc = 0x82
self.cmd = None
self.packet_size = 0 # includes everything from start byte to crc
self.length = 0 # payload part of the packet
self.frame = []
self.address = ''
self.rssi = 0
self.options = ''
self.num_samples = 0
self.a_channels_enabled = []
self.d_channels_enabled = []
self.have_d_channels = False
self.num_a_channels = 0
self.a_channels_data = []
self.d_channels_data = []
def decode_channels(self, channel_ind_1, channel_ind_2):
self.a_channels_enabled = [False for x in range(0,8)]
self.d_channels_enabled = [False for x in range(0,9)]
for bit in range(1, 7):
self.a_channels_enabled[bit-1] = bool(channel_ind_1 & 1 << bit)
self.d_channels_enabled[8] = bool(channel_ind_1 & 1)
for bit in range(0, 7):
self.d_channels_enabled[bit] = bool(channel_ind_2 & 1 << bit)
for i in range(0, len(self.d_channels_enabled)):
self.have_d_channels = self.have_d_channels or self.d_channels_enabled[i]
for i in range(0, len(self.a_channels_enabled)):
self.num_a_channels += int(self.a_channels_enabled[i])
def d_data(self, sample_1, sample_2):
self.d_channels_data[8] = bool(sample_1 & 1)
for bit in range(0, 8):
self.d_channels_data[bit] = bool(sample_2 & 1 << bit)
def a_data(self, msb, lsb):
# ADC is 10 bit
return (msb & 0x3) * 256 + lsb
def decode_packet(self, frame, length):
"""
Decode packet from bytes in frame.
"""
self.frame = frame
try:
self.cmd = frame[0]
if not self.cmd in [self.api_16_bit_adc, self.api_64_bit_adc]:
logger.error( 'Unknown command %0x' % self.cmd)
return
self.length = length
self.packet_size = length + 4
self.address = '%0x%0x' % (frame[1], frame[2])
self.rssi = frame[3]
self.options = frame[4]
self.num_samples = frame[5]
channel_ind_1 = frame[6]
channel_ind_2 = frame[7]
# print '%0x, %0x' % (channel_ind_1, channel_ind_2)
self.decode_channels(channel_ind_1, channel_ind_2)
self.d_channels_data = [0 for x in range(0,9)]
self.a_channels_data = [0 for x in range(0,8)]
frame_byte = 8
for n in range(0, self.num_samples):
if self.have_d_channels:
self.d_data(frame[frame_byte], frame[frame_byte+1])
frame_byte += 2
for adc_idx in range(0, len(self.a_channels_enabled)):
if self.a_channels_enabled[adc_idx]:
self.a_channels_data[adc_idx] += self.a_data(
frame[frame_byte], frame[frame_byte+1])
frame_byte += 2
except IndexError:
logger.error('Invalid XBee API frame: "{0}"'.format(frame))
def get_adc(self, idx):
return self.a_channels_data[idx]
def __str__(self):
res = []
# res.append('frame: %s' % ' '.join(['%0x' % x for x in self.frame]))
res.append('API data packet: ')
if self.cmd is not None:
res.append('cmd=%0x' % self.cmd)
else:
res.append('cmd=None')
res.append('length=%d' % self.length)
res.append('address=%s' % self.address)
res.append('rssi=%d' % self.rssi)
res.append('num.samples=%d' % self.num_samples)
res.append('d channels: D0 [ %s ] D8' %
' '.join([str(int(x)) for x in self.d_channels_enabled]))
res.append('a channels: A0 [ %s ] A7' %
' '.join([str(int(x)) for x in self.a_channels_enabled]))
d_data = []
for idx in range(0, len(self.d_channels_enabled)):
if self.d_channels_enabled[idx]:
d_data.append('D%d=%d'% (idx, self.d_channels_data[idx]))
res.append('d data: %s' % ' '.join(d_data))
a_data = []
for idx in range(0, len(self.a_channels_enabled)):
if self.a_channels_enabled[idx]:
a_data.append('A%d=%d'% (idx, self.a_channels_data[idx]))
res.append('a data: %s' % ' '.join(a_data))
return '\n'.join(res)
def read_packet(serl):
"""
Generator function: reads one XBee API packet from given serial
line and returns it
"""
start_delim = 0x7E
while True:
while True:
c = serl.read()
if c == '':
logger.info('read timeout')
continue
else:
c = ord(c)
# logger.info('read byte: "%0x"' % c)
if c == start_delim:
break
length_high = serl.read()
length_low = serl.read()
length = ord(length_high) * 256 + ord(length_low)
# logger.info('packet length: "%d"' % length)
# lengh includes bytes starting from "83" through the last data byte.
# it does not include 7E 00 1C and checksum (62)
frame = []
for idx in range(0, length):
frame.append(ord(serl.read()))
crc = ord(serl.read())
# logger.info('frame: %s, crc=%0x' % (['%0x' % x for x in frame], crc))
pkt = SerialIOPacket()
pkt.decode_packet(frame, length)
yield pkt