epoinfo

#!/usr/bin/python -uO

import sys
import io
import struct
import time
import argparse

PREAMBLE = 0x2404
COMMAND = 0x02d2
EOW = 0x0a0d
UART_CMD = 253
SATS_PER_EPO = 32
SECONDS_PER_HOUR = 3600
GPS_OFFSET_SECONDS = 315964786
SECONDS_PER_WEEK = 604800
HOURS_PER_WEEK = 168

def Convert2UTC(GPSHour):
    GPSHour *= SECONDS_PER_HOUR
    GPSHour += GPS_OFFSET_SECONDS
    tm = time.gmtime(GPSHour)
    return time.strftime("%Y-%m-%d %H:%M:%S", tm)

def Convert2Local(GPSHour):
    GPSHour *= SECONDS_PER_HOUR
    GPSHour += GPS_OFFSET_SECONDS
    tm = time.localtime(GPSHour)
    return time.strftime("%Y-%m-%d %H:%M:%S", tm)

def crc8(d):
    crc = 0
    for b in bytearray(d):
        crc ^= (b & 0xff)
    return crc

def convert_arg_line_to_args(arg_line):
    for arg in arg_line.split():
        if not arg.strip():
            continue
        yield arg

def main():
    parser = argparse.ArgumentParser(fromfile_prefix_chars='@',
    description="Prints EPO file information",
    epilog="You can use '@filename' to read arguments from a file.")
    parser.convert_arg_line_to_args = convert_arg_line_to_args
    parser.add_argument("input_file", metavar="<EPO_File>", help="EPO data file")
    args = parser.parse_args()

    fi = io.open(args.input_file, mode="rb")
    header = fi.read(75)
    if header[0:3] == header[60:63]:
        print("Opening EPO Type I file")
        EPO_SET_SIZE = 1920
    elif header[0:3] == header[72:75]:
        print("Opening EPO Type II file")
        EPO_SET_SIZE = 2304;
    else:
        print("Unknown file type.")
        return 1
        
    fi.close()
    fi = io.open(args.input_file, mode="rb")
    sets = 0
    
    while True:
        epo_set = fi.read(EPO_SET_SIZE)
        if len(epo_set) == 0:
            break
        sets += 1
        epo_start = struct.unpack("<i", epo_set[0:3]+b'\0')[0]
        if sets == 1:
            start = epo_start
            
        print("Set: %4d.  GPS Wk: %4d  Hr: %3d  Sec:  %6d  %s to %s UTC" % (
            sets, (epo_start / HOURS_PER_WEEK), (epo_start % HOURS_PER_WEEK),
            (epo_start % HOURS_PER_WEEK) * SECONDS_PER_HOUR,
            Convert2UTC(epo_start), Convert2UTC(epo_start + 6)))
        
    fi.close()

    print("%4d EPO sets.  Valid from %s to %s UTC\n" % (sets,
    Convert2UTC(start), Convert2UTC(epo_start + 6)))
    return 0

if __name__ == "__main__":
    sys.exit(main() or 0)