public static int GetPageNumber(TeletextPacketPayload packet)
        {
            var address = (TeletextHamming.UnHamming84(packet.Address[1]) << 4) | TeletextHamming.UnHamming84(packet.Address[0]);
            var m       = address & 0x7;

            if (m == 0)
            {
                m = 8;
            }
            var y = (address >> 3) & 0x1f;

            if (y == 0)
            {
                var i            = (TeletextHamming.UnHamming84(packet.Data[1]) << 4) | TeletextHamming.UnHamming84(packet.Data[0]);
                var flagSubtitle = (TeletextHamming.UnHamming84(packet.Data[5]) & 0x08) >> 3;
                if (flagSubtitle == 1 && i < 0xff)
                {
                    var bcdPage = (m << 8) | (TeletextHamming.UnHamming84(packet.Data[1]) << 4) | TeletextHamming.UnHamming84(packet.Data[0]);
                    return(BcdToDec((ulong)bcdPage));
                }
            }
            return(-1);
        }
        public static void ProcessTelxPacket(DataUnitT dataUnitId, TeletextPacketPayload packet, ulong timestamp, TeletextRunSettings teletextRunSettings, int targetPageNumberBcd, int targetPageNumberDec)
        {
            // variable names conform to ETS 300 706, chapter 7.1.2
            var address = (TeletextHamming.UnHamming84(packet.Address[1]) << 4) | TeletextHamming.UnHamming84(packet.Address[0]);
            var m       = address & 0x7;

            if (m == 0)
            {
                m = 8;
            }

            var y = (address >> 3) & 0x1f;
            var designationCode = y > 25 ? TeletextHamming.UnHamming84(packet.Data[0]) : 0x00;

            if (y == 0) // PAGE HEADER
            {
                // CC map
                var i            = (TeletextHamming.UnHamming84(packet.Data[1]) << 4) | TeletextHamming.UnHamming84(packet.Data[0]);
                var flagSubtitle = (TeletextHamming.UnHamming84(packet.Data[5]) & 0x08) >> 3;

                CcMap[i] |= (byte)(flagSubtitle << (m - 1));

                // Page number and control bits
                var pageNumber = (m << 8) | (TeletextHamming.UnHamming84(packet.Data[1]) << 4) | TeletextHamming.UnHamming84(packet.Data[0]);
                var charset    = ((TeletextHamming.UnHamming84(packet.Data[7]) & 0x08) | (TeletextHamming.UnHamming84(packet.Data[7]) & 0x04) | (TeletextHamming.UnHamming84(packet.Data[7]) & 0x02)) >> 1;
                //uint8_t flag_suppress_header = unham_8_4(packet.data[6]) & 0x01;
                //uint8_t flag_inhibit_display = (unham_8_4(packet.data[6]) & 0x08) >> 3;

                // ETS 300 706, chapter 9.3.1.3:
                // When set to '1' the service is designated to be in Serial mode and the transmission of a page is terminated
                // by the next page header with a different page number.
                // When set to '0' the service is designated to be in Parallel mode and the transmission of a page is terminated
                // by the next page header with a different page number but the same magazine number.
                // The same setting shall be used for all page headers in the service.
                // ETS 300 706, chapter 7.2.1: Page is terminated by and excludes the next page header packet
                // having the same magazine address in parallel transmission mode, or any magazine address in serial transmission mode.
                _transmissionMode = (TransmissionMode)(TeletextHamming.UnHamming84(packet.Data[7]) & 0x01);

                // FIXME: Well, this is not ETS 300 706 kosher, however we are interested in DATA_UNIT_EBU_TELETEXT_SUBTITLE only
                if (_transmissionMode == TransmissionMode.TransmissionModeParallel && dataUnitId != DataUnitT.DataUnitEbuTeletextSubtitle)
                {
                    return;
                }

                if (_receivingData &&
                    (_transmissionMode == TransmissionMode.TransmissionModeSerial && Page(pageNumber) != Page(targetPageNumberBcd) ||
                     _transmissionMode == TransmissionMode.TransmissionModeParallel && Page(pageNumber) != Page(targetPageNumberBcd) && m == Magazine(targetPageNumberBcd))
                    )
                {
                    _receivingData = false;
                    return;
                }

                // Page transmission is terminated, however now we are waiting for our new page
                if (targetPageNumberBcd != pageNumber)
                {
                    return;
                }

                // Now we have the beginning of page transmission; if there is page_buffer pending, process it
                if (_pageBuffer.Tainted)
                {
                    // it would be nice, if subtitle hides on previous video frame, so we contract 40 ms (1 frame @25 fps)
                    _pageBuffer.HideTimestamp = timestamp - 40;
                    ProcessPage(_pageBuffer, teletextRunSettings, targetPageNumberDec);
                }

                _pageBuffer.ShowTimestamp = timestamp;
                _pageBuffer.HideTimestamp = 0;
                _pageBuffer.Text          = new int[25, 40];
                _pageBuffer.Tainted       = false;
                _receivingData            = true;
                _primaryCharset.G0X28     = (int)BoolT.Undef;

                var c = _primaryCharset.G0M29 != (int)BoolT.Undef ? _primaryCharset.G0M29 : charset;
                RemapG0Charset(c);

                /*
                 * // I know -- not needed; in subtitles we will never need disturbing teletext page status bar
                 * // displaying tv station name, current time etc.
                 * if (flag_suppress_header == NO) {
                 *  for (uint8_t i = 14; i < 40; i++) page_buffer.text[y,i] = telx_to_ucs2(packet.data[i]);
                 *  //page_buffer.tainted = YES;
                 * }
                 */
            }
            else if (m == Magazine(targetPageNumberBcd) && y >= 1 && y <= 23 && _receivingData)
            {
                // ETS 300 706, chapter 9.4.1: Packets X/26 at presentation Levels 1.5, 2.5, 3.5 are used for addressing
                // a character location and overwriting the existing character defined on the Level 1 page
                // ETS 300 706, annex B.2.2: Packets with Y = 26 shall be transmitted before any packets with Y = 1 to Y = 25;
                // so page_buffer.text[y,i] may already contain any character received
                // in frame number 26, skip original G0 character
                for (var i = 0; i < 40; i++)
                {
                    if (_pageBuffer.Text[y, i] == 0x00)
                    {
                        _pageBuffer.Text[y, i] = TelxToUcs2(packet.Data[i]);
                    }
                }

                _pageBuffer.Tainted = true;
            }
            else if (m == Magazine(targetPageNumberBcd) && y == 26 && _receivingData)
            {
                // ETS 300 706, chapter 12.3.2: X/26 definition
                var x26Row = 0;

                var triplets = new uint[13];
                var j        = 0;
                for (var i = 1; i < 40; i += 3, j++)
                {
                    triplets[j] = TeletextHamming.UnHamming2418((packet.Data[i + 2] << 16) | (packet.Data[i + 1] << 8) | packet.Data[i]);
                }

                for (var j2 = 0; j2 < 13; j2++)
                {
                    if (triplets[j2] == 0xffffffff)
                    {
                        // invalid data (HAM24/18 uncorrectable error detected), skip group
                        _config.LogError($"! Unrecoverable data error; UNHAM24/18()={triplets[j2]}");
                        continue;
                    }

                    var data            = (triplets[j2] & 0x3f800) >> 11;
                    var mode            = (triplets[j2] & 0x7c0) >> 6;
                    var address2        = triplets[j2] & 0x3f;
                    var rowAddressGroup = address2 >= 40 && address2 <= 63;

                    // ETS 300 706, chapter 12.3.1, table 27: set active position
                    if (mode == 0x04 && rowAddressGroup)
                    {
                        x26Row = (int)(address2 - 40);
                        if (x26Row == 0)
                        {
                            x26Row = 24;
                        }
                    }

                    // ETS 300 706, chapter 12.3.1, table 27: termination marker
                    if (mode >= 0x11 && mode <= 0x1f && rowAddressGroup)
                    {
                        break;
                    }

                    // ETS 300 706, chapter 12.3.1, table 27: character from G2 set
                    int x26Col;
                    if (mode == 0x0f && !rowAddressGroup)
                    {
                        x26Col = (int)address2;
                        if (data > 31)
                        {
                            _pageBuffer.Text[x26Row, x26Col] = TeletextTables.G2[0, data - 0x20];
                        }
                    }

                    // ETS 300 706, chapter 12.3.1, table 27: G0 character with diacritical mark
                    if (mode >= 0x11 && mode <= 0x1f && !rowAddressGroup)
                    {
                        x26Col = (int)address2;
                        if (data >= 65 && data <= 90) // A-Z
                        {
                            _pageBuffer.Text[x26Row, x26Col] = TeletextTables.G2Accents[mode - 0x11, data - 65];
                        }
                        else if (data >= 97 && data <= 122) // a-z
                        {
                            _pageBuffer.Text[x26Row, x26Col] = TeletextTables.G2Accents[mode - 0x11, data - 71];
                        }
                        else // other
                        {
                            _pageBuffer.Text[x26Row, x26Col] = TelxToUcs2((byte)data);
                        }
                    }
                }
            }
            else if (m == Magazine(targetPageNumberBcd) && y == 28 && _receivingData)
            {
                // TODO:
                //   ETS 300 706, chapter 9.4.7: Packet X/28/4
                //   Where packets 28/0 and 28/4 are both transmitted as part of a page, packet 28/0 takes precedence over 28/4 for all but the color map entry coding.
                if (designationCode == 0 || designationCode == 4)
                {
                    // ETS 300 706, chapter 9.4.2: Packet X/28/0 Format 1
                    // ETS 300 706, chapter 9.4.7: Packet X/28/4
                    uint triplet0 = TeletextHamming.UnHamming2418((packet.Data[3] << 16) | (packet.Data[2] << 8) | packet.Data[1]);

                    if (triplet0 == 0xffffffff)
                    {
                        // invalid data (HAM24/18 uncorrectable error detected), skip group
                        _config.LogError($"! Unrecoverable data error; UNHAM24/18()={triplet0}");
                    }
                    else
                    {
                        // ETS 300 706, chapter 9.4.2: Packet X/28/0 Format 1 only
                        if ((triplet0 & 0x0f) == 0x00)
                        {
                            _primaryCharset.G0X28 = (int)((triplet0 & 0x3f80) >> 7);
                            RemapG0Charset(_primaryCharset.G0X28);
                        }
                    }
                }
            }
            else if (m == Magazine(targetPageNumberBcd) && y == 29)
            {
                // TODO:
                //   ETS 300 706, chapter 9.5.1 Packet M/29/0
                //   Where M/29/0 and M/29/4 are transmitted for the same magazine, M/29/0 takes precedence over M/29/4.
                if (designationCode == 0 || designationCode == 4)
                {
                    // ETS 300 706, chapter 9.5.1: Packet M/29/0
                    // ETS 300 706, chapter 9.5.3: Packet M/29/4
                    uint triplet0 = TeletextHamming.UnHamming2418((packet.Data[3] << 16) | (packet.Data[2] << 8) | packet.Data[1]);

                    if (triplet0 == 0xffffffff)
                    {
                        // invalid data (HAM24/18 uncorrectable error detected), skip group
                        _config.LogError($"! Unrecoverable data error; UNHAM24/18()={triplet0}");
                    }
                    else
                    {
                        // ETS 300 706, table 11: Coding of Packet M/29/0
                        // ETS 300 706, table 13: Coding of Packet M/29/4
                        if ((triplet0 & 0xff) == 0x00)
                        {
                            _primaryCharset.G0M29 = (int)((triplet0 & 0x3f80) >> 7);
                            // X/28 takes precedence over M/29
                            if (_primaryCharset.G0X28 == (int)BoolT.Undef)
                            {
                                RemapG0Charset(_primaryCharset.G0M29);
                            }
                        }
                    }
                }
            }
            else if (m == 8 && y == 30)
            {
                // ETS 300 706, chapter 9.8: Broadcast Service Data Packets
                if (!_states.ProgrammeInfoProcessed)
                {
                    // ETS 300 706, chapter 9.8.1: Packet 8/30 Format 1
                    if (TeletextHamming.UnHamming84(packet.Data[0]) < 2)
                    {
                        _config.LogInfoNoNewLine("- Programme Identification Data = ");
                        for (var i = 20; i < 40; i++)
                        {
                            var c = TelxToUcs2(packet.Data[i]);
                            // strip any control codes from PID, eg. TVP station
                            if (c < 0x20)
                            {
                                continue;
                            }
                            _config.LogInfoNoNewLine(Ucs2ToUtf8(c));
                        }
                        _config.LogInfo(string.Empty);

                        // OMG! ETS 300 706 stores timestamp in 7 bytes in Modified Julian Day in BCD format + HH:MM:SS in BCD format
                        // + timezone as 5-bit count of half-hours from GMT with 1-bit sign
                        // In addition all decimals are incremented by 1 before transmission.
                        long t = 0;
                        // 1st step: BCD to Modified Julian Day
                        t += (packet.Data[10] & 0x0f) * 10000;
                        t += ((packet.Data[11] & 0xf0) >> 4) * 1000;
                        t += (packet.Data[11] & 0x0f) * 100;
                        t += ((packet.Data[12] & 0xf0) >> 4) * 10;
                        t += packet.Data[12] & 0x0f;
                        t -= 11111;
                        // 2nd step: conversion Modified Julian Day to unix timestamp
                        t = (t - 40587) * 86400;
                        // 3rd step: add time
                        t += 3600 * (((packet.Data[13] & 0xf0) >> 4) * 10 + (packet.Data[13] & 0x0f));
                        t += 60 * (((packet.Data[14] & 0xf0) >> 4) * 10 + (packet.Data[14] & 0x0f));
                        t += ((packet.Data[15] & 0xf0) >> 4) * 10 + (packet.Data[15] & 0x0f);
                        t -= 40271;
                        // 4th step: conversion to time_t
                        var span      = TimeSpan.FromTicks(t * TimeSpan.TicksPerSecond);
                        var t2        = new DateTime(1970, 1, 1).Add(span);
                        var localTime = TimeZoneInfo.ConvertTimeFromUtc(t2, TimeZoneInfo.Local);

                        _config.LogInfo($"- Programme Timestamp (UTC) = {localTime.ToLongDateString()} {localTime.ToLongTimeString()}");
                        _config.LogInfo($"- Transmission mode = {(_transmissionMode == TransmissionMode.TransmissionModeSerial ? "serial" : "parallel")}");
                        _states.ProgrammeInfoProcessed = true;
                    }
                }
            }
        }