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DSCrx-v02.py
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DSCrx-v02.py
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import sys
import time
import pyaudio
import numpy as np
import json
############################################################################################################################################
# Configuration
SAMPLE_RATE = 44100 # Sample rate of soundcard
CENTER_FREQUENCY = 1700 # 1700 for VHF, center frequency for MF - HF (for example 800 or 1000)
SHIFT_FREQUENCY = 800 # 800 for VHF
BIT_RATE = 1200.0 # Bitrate 1200 for VHF
############################################################################################################################################
# Global Variables
AUDIO_SIGNAL = [] # Audio trace channel 1
RUN_STATUS = 1 # 0 stopped, 1 start, 2 running, 3 stop now, 4 stop and restart
RX_BUFFER = 0.0 # Data contained in input buffer in %
NEXT_BIT_TIME = 0.0 # The next bit sample time moment in samples
YBY_TIMES = [0.0, 1.0, 2.0, 3.0] # Zero crossing times
YBY_VALUES = [1.0, 1.0] # Sample values for zero crossings
YBY_STATES = ["P", "N"] # Sample states for positive/negative period
STR_YBY = "" # The YBY string from the YBY decoding process
MSG_DATA = [] # The message data
EXP_MSG_DATA = [] # Extension message data
MSG = 0 # Start of message position
MSG_STATUS = 0 # 0=Search Phasing; 1=Decode Data; 2=Decode to Message; 3=Error in Message decoding
############################################################################################################################################
# Initialize PyAudio
PA = pyaudio.PyAudio()
FORMAT = pyaudio.paInt16
# =============== The Main Loop =====================
def main_loop():
global MSG_DATA
while True:
make_yby() # Decode audio data in AUDIO_SIGNAL to YBY
find_phasing() # Search for the phasing signal and the start of a message
make_data() # Create data and call message decoders
print(MSG_DATA)
if MSG_STATUS == 2:
json_message = decode_dsc_message(MSG_DATA)
print(json_message)
# ======================= Read audio from stdin ==================================
def audio_in():
global AUDIO_SIGNAL, RUN_STATUS, SAMPLE_RATE
if RUN_STATUS == 1:
AUDIO_SIGNAL = []
chunkbuffer = SAMPLE_RATE * 4 # Fixed at xx seconds
readsamples = SAMPLE_RATE # Samples to read
RUN_STATUS = 2
print(f"Reading audio from stdin\nSample rate: {SAMPLE_RATE} samples/s")
if RUN_STATUS == 2:
try:
signals = sys.stdin.buffer.read(SAMPLE_RATE * 2) # 2 bytes per sample
if signals:
AUDIO_SIGNAL.extend(np.frombuffer(signals, np.int16))
else:
RUN_STATUS = 4
print("No audio data received from stdin")
except IOError:
pass # Ignore IOError if no data available
except Exception as e:
RUN_STATUS = 4
print(f"Audio buffer reset! Error: {e}")
if RUN_STATUS in [3, 4]:
PA.terminate()
print("Audio Stream stopped!")
RUN_STATUS = 1 if RUN_STATUS == 4 else 0
AUDIO_SIGNAL = [] # Clear audio buffer
# ============= Convert AUDIO_SIGNAL audio data to STR_YBY =======================
def make_yby():
global STR_YBY, AUDIO_SIGNAL, NEXT_BIT_TIME, YBY_TIMES, YBY_VALUES, YBY_STATES
low_frequency = CENTER_FREQUENCY - SHIFT_FREQUENCY / 2.0
high_frequency = CENTER_FREQUENCY + SHIFT_FREQUENCY / 2.0
low_samples = SAMPLE_RATE / low_frequency
high_samples = SAMPLE_RATE / high_frequency
decision = high_samples + (low_samples - high_samples) / 4.25
bit_time_step = SAMPLE_RATE / BIT_RATE
add_yby = 0
i = 0
while add_yby < 50:
while len(AUDIO_SIGNAL) <= i:
audio_in()
v = AUDIO_SIGNAL[i]
current_sample = "P" if v >= 0 else "N"
if current_sample != YBY_STATES[0]: # A zero crossing
YBY_STATES[0] = current_sample
YBY_VALUES[1] = abs(v)
y = YBY_VALUES[1] / (YBY_VALUES[0] + YBY_VALUES[1])
YBY_TIMES = YBY_TIMES[1:] + [i - y]
if (YBY_TIMES[2] - YBY_TIMES[0]) >= decision and (YBY_TIMES[3] - YBY_TIMES[1]) < decision:
if (NEXT_BIT_TIME - YBY_TIMES[1]) < bit_time_step / 2.0:
NEXT_BIT_TIME += bit_time_step * 0.025
else:
NEXT_BIT_TIME -= bit_time_step * 0.025
while NEXT_BIT_TIME < YBY_TIMES[2]:
add_yby += 1
NEXT_BIT_TIME += bit_time_step
STR_YBY += "B" if (YBY_TIMES[2] - YBY_TIMES[0]) < decision or (YBY_TIMES[3] - YBY_TIMES[1]) < decision else "Y"
YBY_VALUES[0] = abs(v)
if i > (NEXT_BIT_TIME + 2 * bit_time_step):
add_yby += 1
NEXT_BIT_TIME = i + bit_time_step
STR_YBY += "Y"
YBY_TIMES = [i - bit_time_step * x for x in range(4)]
i += 1
AUDIO_SIGNAL = AUDIO_SIGNAL[i:] # Delete used samples
NEXT_BIT_TIME -= i
YBY_TIMES = [x - i for x in YBY_TIMES]
print(f"make_yby() called, STR_YBY extended: {STR_YBY}")
# ================== Start Decoding routines =====================================================
# ============= Find the phasing signal and the start of the message MSG =======================
def find_phasing():
global STR_YBY
global MSG # Start of message in STR_YBY
global RUN_STATUS
if RUN_STATUS != 0 and RUN_STATUS != 3: # Exit if MSGstatus not 0 or 3 (not necessary)
return()
# ... Find Phasing ...
MinBits = 50 # The minimum of bits in the YBY string (> 20)
Starti = 100 # Start to search from this pointer, so that the data before this pointer can also be read
if RUN_STATUS == 3: # Start of new search, skip the old part upto the format specifier
STR_YBY = STR_YBY[(MSG+120-Starti):] # Ready for next search of phasing signal
RUN_STATUS = 0 # And set the status to search
while len(STR_YBY) < (Starti+MinBits+21): # If STR_YBY is too short, call MakeYBY
make_yby()
se1 = ten_unit(108) + ten_unit(125) # Define search string 1 for phasing
se2 = ten_unit(107) + ten_unit(125) # Define search string 2 for phasing
i = Starti
L = len(STR_YBY)
while i < (L - MinBits):
if STR_YBY[i:(i+20)] == se1:
MSG = i - 70
RUN_STATUS = 1
break
if STR_YBY[i:(i+20)] == se2:
MSG = i - 90
RUN_STATUS = 1
break
i = i + 1
if RUN_STATUS == 0:
STR_YBY= STR_YBY[(L - MinBits - Starti):]
return()
# ============= MAKEdata, set the data into MSG_DATA =======================
def make_data():
global MSG_DATA, EXP_MSG_DATA, MSG, MSG_STATUS
if MSG_STATUS != 1:
return
fs1 = get_val_symbol(13)
if fs1 < 100:
fs1 = get_val_symbol(18)
fs2 = get_val_symbol(15)
if fs2 < 100:
fs2 = get_val_symbol(20)
if fs1 != fs2:
MSG_STATUS = 3
print("Format specifiers not identical")
return
msg_data = [fs1]
l3b_error = False
v_previous = -1
i = 17
while True:
v = get_val_symbol(i)
if v < 0:
v = get_val_symbol(i + 5)
if v >= 0:
msg_data.append(v)
else:
l3b_error = True
break
if v_previous in [117, 122, 127]:
break
v_previous = v
i += 2
start_exp_msg = i + 6
if l3b_error:
print("Error Character Check 3 last bits (2x)")
MSG_STATUS = 3
return
ecc = msg_data[0]
for symbol in msg_data[1:-1]:
ecc ^= symbol
if msg_data[-1] != ecc:
print("Data does not match with Error Check Character")
MSG_STATUS = 3
return
MSG_DATA = msg_data
MSG_STATUS = 2
v = get_val_symbol(start_exp_msg)
if not (100 <= v <= 106):
EXP_MSG_DATA = []
return
exp_msg_data = []
l3b_error = False
v_previous = -1
i = start_exp_msg
while True:
v = get_val_symbol(i)
if v < 0:
v = get_val_symbol(i + 5)
if v >= 0:
exp_msg_data.append(v)
else:
l3b_error = True
break
if v_previous in [117, 122, 127]:
break
v_previous = v
i += 2
if l3b_error:
print("Error in Extended Data, 3 last bits")
EXP_MSG_DATA = []
return
ecc = exp_msg_data[0]
for symbol in exp_msg_data[1:-1]:
ecc ^= symbol
if exp_msg_data[-1] != ecc:
print("Error Check Character in Extended Data does not match")
EXP_MSG_DATA = []
return
EXP_MSG_DATA = exp_msg_data
# ======================= Decode the DSC MSG_DATA to a JSON message =======================
def decode_dsc_message(dsc_array):
if len(dsc_array) < 22:
raise ValueError("Array does not contain enough elements to decode a DSC message.")
mmsi = ''.join([str(x) for x in dsc_array[0:9]])
category_code = dsc_array[9]
category_map = {
100: "Routine",
108: "Safety",
110: "Urgency",
112: "Distress"
}
category = category_map.get(category_code, "Unknown")
# Decode nature of distress if category is Distress
nature_of_distress = None
if category == "Distress":
nature_of_distress = dsc_array[10]
nature_of_distress_map = {
100: "Undesignated",
101: "Fire, explosion",
102: "Flooding",
103: "Collision",
104: "Grounding",
105: "Listing, in danger of capsizing",
106: "Sinking",
107: "Disabled and adrift",
108: "Abandoning ship",
109: "Man overboard",
110: "Piracy/armed attack",
112: "Medical assistance"
}
nature_of_distress = nature_of_distress_map.get(nature_of_distress, "Unknown")
# Decode Latitude
lat_deg = dsc_array[11]
lat_min = dsc_array[12]
lat_dir = 'N' if dsc_array[13] <= 89 else 'S'
latitude = f"{lat_deg}°{lat_min}'{lat_dir}"
# Decode Longitude
lon_deg = dsc_array[14]
lon_min = dsc_array[15]
lon_dir = 'E' if dsc_array[16] <= 179 else 'W'
longitude = f"{lon_deg}°{lon_min}'{lon_dir}"
# UT Time
utc_hour = dsc_array[17]
utc_minute = dsc_array[18]
utc_time = f"{utc_hour:02}:{utc_minute:02}"
# Additional Data (example, EOS, VHF channels etc.)
eos = dsc_array[19]
vhf_rx_channel = dsc_array[20]
vhf_tx_channel = dsc_array[21]
message = {
"MMSI": mmsi,
"Category": category,
"Latitude": latitude,
"Longitude": longitude,
"UTC Time": utc_time,
"EOS": eos,
"VHF RX Channel": vhf_rx_channel,
"VHF TX Channel": vhf_tx_channel
}
if nature_of_distress:
message["Nature of Distress"] = nature_of_distress
return json.dumps(message, indent=4)
# ========== Helper functions for decoding =================================
def get_val_symbol(pos):
global STR_YBY
try:
return symbol_val(STR_YBY[pos:(pos + 10)])
except IndexError:
return -1
def symbol_val(x):
if len(x) < 10:
return -1
bits = [1 if c == 'Y' else 0 for c in x]
vals = [64, 32, 16, 8, 4, 2, 1]
return sum([b * v for b, v in zip(bits[1:], vals)]) if bits[0] else -1
def ten_unit(Vin):
if (Vin > 127):
return("ERROR ten_unit > 127") # ERROR
intB = 0
intY = 1
Vout = ""
n = 0
while (n < 7): # Calculate the first 7 bits, msb(Y=1) first
if (int(Vin) & int(intY)) != 0:
Vout = Vout + "Y"
else:
Vout = Vout + "B"
intB = intB + 1 #Counts the number of B's (B=0)
intY = intY * 2
n = n + 1
intY = 4
n = 0
while (n < 3): # Calculate the last 3 bits from intB (the number of "B"s), Msb(Y=1) first
if (int(intB) & int(intY)) != 0:
Vout = Vout + "Y"
else:
Vout = Vout + "B"
intY = intY / 2
n = n + 1
return(Vout)
# ========== Start the main loop =====================
main_loop()