def ExBusPacket(self, packet_ID):
self.exbus_packet = bytearray()
# toggles True and False
self.get_new_sensor ^= True
# send data and text messages for each sensor alternating
if self.get_new_sensor:
# get next sensor to send its data
self.current_sensor = next(self.next_sensor)
current_EX_type = 'data'
else:
current_EX_type = 'text'
# get the EX packet for the current sensor
ex_packet = self.jetiex.ExPacket(self.current_sensor, current_EX_type)
# EX bus header
self.exbus_packet.extend(b'3B01')
# EX bus packet length in bytes including the header and CRC
exbus_packet_length = 8 + len(ex_packet)
self.exbus_packet.extend('{:02x}'.format(exbus_packet_length))
# packet ID (answer with same ID as by the request)
# FIXME
# FIXME check how this works with data and 2x text from EX values???
# FIXME
int_ID = int(str(packet_ID), 16)
bin_ID = '{:02x}'.format(int_ID)
self.exbus_packet.extend(bin_ID)
# telemetry identifier
self.exbus_packet.extend(b'3A')
# packet length in bytes of EX packet
ex_packet_length = len(ex_packet)
self.exbus_packet.extend('{:02x}'.format(ex_packet_length))
# add EX packet
self.exbus_packet.extend(ex_packet)
# calculate the crc for the packet
crc = CRC16.crc16_ccitt(self.exbus_packet)
# compile final telemetry packet
self.exbus_packet.extend(crc[2:4])
self.exbus_packet.extend(crc[0:2])
# print('Ex Bus Packet (JetiExBus.py)', self.jetiex.bytes2hex(self.exbus_packet))
# print('Ex Bus Packet (JetiExBus.py)', self.exbus_packet)
return self.exbus_packet
def checkCRC(self, packet, crc_check):
'''Do a CRC check using CRC16-CCITT
Args:
packet (bytearray): packet of Jeti Ex Bus including the checksum
The last two bytes of the packet are LSB and
MSB of the checksum.
Returns:
bool: True if the crc check is OK, False if NOT
'''
crc = CRC16.crc16_ccitt(packet)
return crc == crc_check
def checkSpeed(self):
'''Check the connection speed via CRC. This needs to be done by
the sensor (slave). The speed is either 125000 (default) or 250000
- if CRC ok, then speed is ok
- if CRC is not ok, then speed has to be set to the
respective 'other' speed
Args:
packet (bytes): one complete packet received from the
Jeti receiver (master)
Returns:
bool: information if speed check was ok or failed
'''
# do the same as in run_forever
while True:
self.exbus = self.serial.read(8)
self.checkTelemetryRequest()
# EX bus CRC starts with first byte of the packet
offset = 0
# packet to check is message without last 2 bytes
packet = bytearray(self.telemetryRequest[:-2])
# the last 2 bytes of the message makeup the crc value for the packet
packet_crc = self.telemetryRequest[-2:]
# calculate the crc16-ccitt value of the packet
crc = CRC16.crc16_ccitt(packet)
if crc == packet_crc:
speed_changed = False
else:
# change speed if CRC check fails
speed_changed = True
if self.baudrate == 125000:
self.baudrate = 250000
elif self.baudrate == 250000:
self.baudrate = 125000
return speed_changed