def make_position_frame(metype, addr, elat, elon, ealt, oddflag):
"""Create single DF17 position frame"""
frame = bytearray(14)
frame[0] = (17 << 3) | (5) # DF, CA
frame[1] = (addr >> 16) & 255 # AA
frame[2] = (addr >> 8) & 255 # AA
frame[3] = addr & 255 # AA
frame[4] = (metype << 3) # ME type, status 0, SAF 0
frame[5] = (ealt >> 4) & 255 # Altitude (MSB)
frame[6] = (ealt & 15) << 4 # Altitude (LSB)
if oddflag:
frame[6] |= 4 # CPR format
frame[6] |= (elat >> 15) & 3 # CPR latitude (top bits)
frame[7] = (elat >> 7) & 255 # CPR latitude (middle bits)
frame[8] = (elat & 127) << 1 # CPR latitude (low bits)
frame[8] |= (elon >> 16) & 1 # CPR longitude (high bit)
frame[9] = (elon >> 8) & 255 # CPR longitude (middle bits)
frame[10] = elon & 255 # CPR longitude (low bits)
# CRC
c = _modes.crc_residual(frame)
frame[11] = (c >> 16) & 255
frame[12] = (c >> 8) & 255
frame[13] = c & 255
return frame
def make_velocity_frame(addr, nsvel, ewvel, vrate):
"""Create a DF17 airborne velocity frame"""
supersonic = (nsvel is not None and abs(nsvel) > 1000) or (ewvel is not None and abs(ewvel) > 1000)
e_ns = encode_velocity(nsvel, supersonic)
e_ew = encode_velocity(ewvel, supersonic)
e_vr = encode_vrate(vrate)
frame = bytearray(14)
frame[0] = (17 << 3) | (5) # DF, CA
frame[1] = (addr >> 16) & 255 # AA
frame[2] = (addr >> 8) & 255 # AA
frame[3] = addr & 255 # AA
frame[4] = (19 << 3) # ES type 19, airborne velocity
if supersonic:
frame[4] |= 2 # subtype 2, ground speed, supersonic
else:
frame[4] |= 1 # subtype 1, ground speed, subsonic
frame[5] = (e_ew >> 8) & 7 # intent change 0, IFR 0, NUCr 0, E/W velocity top bits
frame[6] = (e_ew & 255) # E/W velocity low bits
frame[7] = (e_ns >> 3) & 255 # N/S velocity top bits
frame[8] = (e_ns & 7) << 5 # N/S velocity low bits
frame[8] |= 16 # vertical rate source = baro
frame[8] |= (e_vr >> 6) & 15 # vertical rate top bits
frame[9] = (e_vr & 63) << 2 # vertical rate low bits
frame[10] = 0 # GNSS/Baro alt offset, no data
# CRC
c = _modes.crc_residual(frame)
frame[11] = (c >> 16) & 255
frame[12] = (c >> 8) & 255
frame[13] = c & 255
return frame
