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Lx0&Lx6&LC86L&LG77L AGNSS Application Note GNSS Module Series Version: 1.2 Date: 2022-05-09 Status: Released GNSS Module Series At Quectel, our aim is to provide timely and comprehensive services to our customers. If you require any assistance, please contact our headquarters: Quectel Wireless Solutions Co., Ltd. Building 5, Shanghai Business Park Phase III (Area B), No.1016 Tianlin Road, Minhang District, Shanghai 200233, China Tel: +86 21 5108 6236 Email: info@quectel.com Or our local offices. For more information, please visit: http://www.quectel.com/support/sales.htm. For technical support, or to report documentation errors, please visit: http://www.quectel.com/support/technical.htm. Or email us at: support@quectel.com. Legal Notices We offer information as a service to you. The provided information is based on your requirements and we make every effort to ensure its quality. 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Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 2 / 47 GNSS Module Series About the Document Document Information Title Lx0&Lx6&LC86L&LG77L AGNSS Application Note Subtitle GNSS Module Series Document Type Application Note Document Status Released Revision History Version 1.0 Date 2017-04-28 2017-04-28 1.1 2021-11-22 1.2 2022-05-09 Description Creation of the document First official release 1. Modified the structure of the document. 2. Added information on Host EPO including the difference between Host EPO and Flash EPO, AGNSS implementation with Host EPO and relevant example, and Host EPO testing with QGNSS. 3. Added applicable modules (L26, L76, L76-L, L86, L96, L26-LB, L76-LB, L70, L80, L70-R, L80-R, LC86L and LG77L). 4. Added AGNSS requirements (Chapter 1.3). 5. Added the structure of Binary Protocol (Figure 5). 6. Added the description of Binary Protocol fields (Table 6). 7. Added AGNSS procedure with Flash EPO and description of the procedure (Chapter 3.1.3). 8. Added the following messages PMTK127, PMTK713, PMTK721, PMTK740 and PMTK741 (Chapter 4). 9. Added the content of Flash EPO testing with QGNSS (Chapter 5.1). 10. Added the example on Flash EPO implementation (Chapter 6.1). 11. Deleted the description of error handing in data transfer procedure. 1. Added a note for MTK_BIN_ACK_EPO (Chapter 3.1.1.1). Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 3 / 47 GNSS Module Series 2. Modified the description of Result in MTK_BIN_EPO (Table 13). 3. Added optional extended parameters for PMTK_ACK (Chapter 4.1). Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 4 / 47 GNSS Module Series Contents About the Document ................................................................................................................................... 3 Contents ....................................................................................................................................................... 5 Table Index................................................................................................................................................... 7 Figure Index ................................................................................................................................................. 8 1 Introduction .......................................................................................................................................... 9 1.1. Differences Between Host EPO and Flash EPO....................................................................... 9 1.2. Applicable Modules ................................................................................................................. 10 1.3. AGNSS Requirements............................................................................................................. 11 2 Download of EPO Files...................................................................................................................... 12 2.1. Get EPO Files from Server...................................................................................................... 12 2.2. EPO Files Format .................................................................................................................... 13 2.2.1. EPO Files Format – GPS Only ...................................................................................... 13 2.2.2. EPO Files Format – GPS + GLONASS ......................................................................... 14 2.3. Types of EPO Files .................................................................................................................. 15 2.4. Recommended Download Procedures of EPO Files .............................................................. 16 2.5. The Validity Period of EPO Files ............................................................................................. 16 3 AGNSS Implementation..................................................................................................................... 18 3.1. AGNSS with Flash EPO .......................................................................................................... 18 3.1.1. Binary Protocol ............................................................................................................... 18 3.1.1.1. MTK_BIN_EPO (MsgID = 723)............................................................................... 19 3.1.1.2. MTK_BIN_ACK_EPO (Msg = 2) ............................................................................. 20 3.1.1.3. Change UART Format Packet (MsgID = 253) ........................................................ 21 3.1.1.4. ACK Packet (MsgID = 1)......................................................................................... 22 3.1.2. EPO Data Transfer Protocol .......................................................................................... 23 3.1.2.1. Pseudo Code for EPO Data Transfer Protocol ....................................................... 23 3.1.3. AGNSS Procedure with Flash EPO ............................................................................... 26 3.2. AGNSS with Host EPO............................................................................................................ 27 3.2.1. Recommended Sequence for Host EPO ....................................................................... 27 3.2.2. Sample Code of Sending EPO ...................................................................................... 28 4 AGNSS Related Messages ................................................................................................................ 31 4.1. PMTK001 PMTK_ACK ............................................................................................................ 31 4.2. PMTK127 PMTK_CMD_CLEAR_EPO.................................................................................... 31 4.3. PMTK253 PMTK_SET_OUTPUT_FMT .................................................................................. 32 4.4. PMTK607 PMTK_Q_EPO_INFO ............................................................................................ 33 4.5. PMTK707 PMTK_DT_EPO_INFO .......................................................................................... 34 4.6. PMTK713 PMTK_DT_LOC ..................................................................................................... 35 4.7. PMTK721 PMTK_DT_SV_EPO .............................................................................................. 36 4.8. PMTK740 PMTK_DT_UTC ..................................................................................................... 37 4.9. PMTK741 PMTK_DT_POS ..................................................................................................... 37 Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 5 / 47 GNSS Module Series 5 EPO Usage Through QGNSS ............................................................................................................ 39 5.1. Testing Flash EPO with QGNSS ............................................................................................. 39 5.2. Testing Host EPO with QGNSS............................................................................................... 41 6 AGNSS Implementation Example..................................................................................................... 43 6.1. Flash EPO Implementation...................................................................................................... 43 6.2. Host EPO Implementation ....................................................................................................... 44 7 Appendix References ........................................................................................................................ 47 Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 6 / 47 GNSS Module Series Table Index Table 1: Differences Between Flash EPO and Host EPO ........................................................................... 9 Table 2: Type of EPO Supported on Applicable Modules .......................................................................... 10 Table 3: AGNSS Related Commands .........................................................................................................11 Table 4: Download URL of EPO Files ........................................................................................................ 12 Table 5: Types of EPO Files ....................................................................................................................... 15 Table 6: Description of Binary Protocol Fields ........................................................................................... 19 Table 7: MTK_BIN_EPO Format ................................................................................................................ 19 Table 8: Format for MTK_BIN_EPO with 2 SAT Data................................................................................ 20 Table 9: Format for MTK_BIN_EPO with 1 SAT Data................................................................................ 20 Table 10: Format for MTK_BIN_EPO with No SAT Data ........................................................................... 20 Table 11: Description of MTK_BIN_EPO Fields......................................................................................... 20 Table 12: MTK_BIN_ACK_EPO Format .................................................................................................... 21 Table 13: Description of MTK_BIN_ACK_EPO Fields ............................................................................... 21 Table 14: Format for Change UART Format Packet.................................................................................. 21 Table 15: Description of Change UART Format Packet Fields.................................................................. 22 Table 16: ACK Packet Format .................................................................................................................... 22 Table 17: Description of ACK Packet Fields .............................................................................................. 23 Table 18: Almanac, Ephemeris and EPO................................................................................................... 47 Table 19: Terms and Abbreviations ............................................................................................................ 47 Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 7 / 47 GNSS Module Series Figure Index Figure 1: EPO Files Format – GPS Only ................................................................................................... 13 Figure 2: Format for Several Segments of EPO Files ............................................................................... 14 Figure 3: EPO Files Format – GPS + GLONASS ...................................................................................... 14 Figure 4: Recommended Download Procedures of EPO Files ................................................................. 16 Figure 5: Structure of Binary Protocol........................................................................................................ 18 Figure 6: AGNSS Procedure with Flash EPO ............................................................................................ 26 Figure 7: Recommended Sequence for Host EPO.................................................................................... 28 Figure 8: AGNSS Setting Interface of QGNSS .......................................................................................... 39 Figure 9: EPO File Downloading................................................................................................................ 40 Figure 10: Static TTFF Testing ................................................................................................................... 40 Figure 11: TTFF Setting ............................................................................................................................. 41 Figure 12: Static TTFF Testing ................................................................................................................... 41 Figure 13: TTFF Setting ............................................................................................................................. 42 Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 8 / 47 GNSS Module Series 1 Introduction EPOTM (Extended Prediction Orbit) is an AGNSS feature provided by the chipset supplier, which can improve sensitivity and shorten TTFF. This document mainly describes the download of EPOTM files, AGNSS implementation, EPOTM related PMTK commands and how to evaluate the EPOTM functionality through QGNSS tool. 1.1. Differences Between Host EPO and Flash EPO Both Flash EPO and Host EPO allow the GNSS receiver to achieve a shorter TTFF, but their differences make each of them suitable for different applications. Host EPO (also called Real Time AGNSS) allows the receiver to store in RAM up to 6 hours of assistance data which are sent to the receiver through NMEA PMTK commands listed in Chapter 4. For Host EPO, there is no data retention after the GNSS receiver reboots and the data should be re-downloaded. Flash EPO, on the other hand, allows the receiver to store in flash 7 or 14 days’ assistance data which are sent to the receiver through Binary Protocol defined by the chipset supplier. Flash EPO enables the receiver to reuse all assistance information stored in flash before the information expires. See Chapter 2.5 for the validity period of EPO files. Table 1: Differences Between Flash EPO and Host EPO Item Storage Space Storage Capacity Protocol Flash EPO Flash 7 or 14 days’ assistance data Binary Host EPO RAM 6 hours’ assistance data NMEA Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 9 / 47 GNSS Module Series NOTE The maximum period that EPO data can be stored in flash is 14 days for GPS-only EPO files, and 7 days for GPS+GLONASS EPO files. If a 30-day GPS-only EPO file is sent, only the first 14 days of EPO data will be stored. If a 30-day GPS+GLONASS EPO file is sent, only the first 7 days of EPO data will be stored. 1.2. Applicable Modules Not all the applicable modules support both Flash EPO and Host EPO. See the following table for the applicable modules of this document and the type of EPO supported on each module. Table 2: Type of EPO Supported on Applicable Modules Series Lx0 Lx6 LC86L LG77L Module L70 L80 L70-R L80-R L26 L76 L76-L L86 L96 L26-LB L76-LB LC86L LG77L Flash EPO            Host EPO              Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 10 / 47 GNSS Module Series 1.3. AGNSS Requirements The host needs to provide the Reference Time, Reference Position and EPO data to the GNSS receiver. The information provided by the host needs to meet the following requirements so that the GNSS receiver can make better use of EPO: ⚫ The Reference Time should be accurate within 3 s and must be specified in UTC time. ⚫ The Reference Position should be accurate within 30 km from the receiver actual location. Keep in mind that if the receiver’s view of the sky is limited, the accuracy of the Reference Position needs to be increased. ⚫ The EPO data should be valid. The receiver can benefit from any of the assistance data to improve the TTFF. All assistance data (Reference Time, Reference Position and EPO data) are useful but none of them are mandatory. If some of them are unavailable or have expired, it is recommended to avoid using them. The host can send the Reference Time, Reference Position and EPO data to the GNSS receiver through the messages listed in following table. See Chapter 4 for a detailed description of these messages. Table 3: AGNSS Related Commands Packet Type PMTK713 PMTK721 PMTK740 PMTK741 Data Content Reference Position. GPS/GLONASS EPO data for a single satellite. Reference UTC Time. Reference Time and Position. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 11 / 47 GNSS Module Series 2 Download of EPO Files Quectel does not provide any Service Level Agreement for EPO files. Quectel is asking users to download EPO data to their own servers and send them to devices so as to ensure the availability of EPO data. 2.1. Get EPO Files from Server Table 4: Download URL of EPO Files EPO Type Unified QEPO Unified QEPO EPO EPO GNSS Type GPS only GPS + GLONASS GPS only GPS + GLONASS EPO File URL File Name http://wpepodownload.mediatek.com/ QGPS.DAT?vendorinfo http://wpepodownload.mediatek.com/ QG_R.DAT?vendorinfo http://wpepodownload.mediatek.com/ EPO_GPS_3_X.DAT?vendorinfo http://wpepodownload.mediatek.com/ EPO_GR_3_X.DAT?vendorinfo Single name: QGPS.DAT Single name: QG_R.DAT X = 1–10 EPO_GPS_3_1.DAT to EPO_GPS_3_10.DAT X = 1–10 EPO_GR_3_1.DAT to EPO_GR_3_10.DAT The following shows a complete URL sample: http://wpepodownload.mediatek.com/QGPS.DAT?vendor=AAA&project=BBB&device_id=CCC ⚫ The query string starts with '?' and is separated by '&'. ⚫ The values of 'vendor' and 'project' (AAA, BBB in the example) are issued by Quectel, contact Quectel Technical Support to get the value. ⚫ The value of 'device_id' (CCC in the example) contains two parts – one is assigned by Quectel and the other assigned by users. For example: if CCC = XXX_YYY, the value XXX is provided by Quectel and users can contact Quectel Technical Support to get the value, while YYY can be assigned by users and it must be a unique value, such as IMEI. Each device must have a unique ID. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 12 / 47 GNSS Module Series NOTE As there can be a maximum of 30 days’ predictions, there will be up to 10 files. Slices of 30-day EPO: _1 for days 1 to 3, _2 for days 4 to 6, ... _10 for days 28 to 30. 2.2. EPO Files Format This part mainly illustrates the format of EPO files for GPS only and for GPS + GLONASS. 2.2.1. EPO Files Format – GPS Only Day1 Day2 ... Day29 Day30 EPO Format (1 day) Segment UTC Segment1 0:00-6:00 Segment2 6:00-12:00 Segment3 12:00-18:00 Segment4 18:00-24:00 EPO Format (1 Segment) SV1 SV2 ... SV31 SV32 EPO Format (1 SV) Data GPS_Hour ... Byte offset 0[LSB]~2[MSB] 3 Data ... Byte offset ... ... 4~7 ... 64~67 ... 8~11 CheckSum 68~71 Figure 1: EPO Files Format – GPS Only GPS_Secs = GPS_Hour * 3600 GPS_Week Number = GPS_Secs / 604800 GPS TOW = GPS_Secs % 604800 Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 13 / 47 SAT data SAT data GNSS Module Series An EPO file contains GPS Time (GPS_Week, GPS_Hour and GPS_Secs). The maximum unit in GPS Time is GPS week which starts at approximately midnight of January 5th to 6th, 1980. The following figure illustrates the format for several segments of EPO files. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 EPO SET 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 EPO SET 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 EPO SET Figure 2: Format for Several Segments of EPO Files The basic unit of an EPO file is SAT Data and the size of each SAT Data is 72 bytes. One EPO SET contains 32 SAT Data, so the data size of an EPO SET is 2304 bytes. Each EPO file contains several EPO SETs, so the file size must be a multiple of 2304 bytes. An EPO SET is valid for 6 hours. Therefore, there will be 4 EPO SETs for one day. 2.2.2. EPO Files Format – GPS + GLONASS SAT data SAT data 1 2 1 2 31 32 65 66 31 32 65 66 87 88 87 88 1 2 31 32 65 66 87 88 GPS EPO SET GLONASS EPO SET Figure 3: EPO Files Format – GPS + GLONASS The basic unit of an EPO file is SAT Data, and the size of a SAT Data is 72 bytes. In GPS + GLONASS EPO files, one EPO SET contains 56 SAT Data, so the data size for an EPO SET is 4032 bytes. Each Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 14 / 47 GNSS Module Series EPO file contains several EPO SETs. The file size must be a multiple of 4032 bytes. An EPO SET is valid for 6 hours. Therefore, there will be 4 EPO SETs for one day. 2.3. Types of EPO Files The EPO data can be downloaded in the form of files. Users can select the most suitable file to download based on the availability of a data connection and storage space of the application. See Table 4: Download URL of EPO Files and Table 5: Types of EPO Files to decide on the file type to be downloaded. Table 5: Types of EPO Files EPO Type Unified QEPO GNSS Type GPS only Unified QEPO GPS + GLONASS EPO EPO GPS only GPS + GLONASS Description 6-hour prediction orbit (ephemeris). Single file containing the latest GPS EPO data available. 6-hour prediction orbit (ephemeris). Single file containing the latest GPS + GLONASS EPO data available. 3-30 days’ prediction orbit (ephemeris). Split in 10 files and each contains 3-day information. 3-30 days’ prediction orbit (ephemeris). Split in 10 files and each contains 3-day information. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 15 / 47 GNSS Module Series 2.4. Recommended Download Procedures of EPO Files Set daily timer to check EPO effectiveness Daily timer expires Power on GNSS receiver Will EPO files expire today?1) Yes Download 3-day EPO files for back up Have valid EPO files?3) Yes No Download unified QEPO files EPO aiding with backup file Verify downloaded Data2) Verify downloaded data Position fixed Backup prepared EPO files Position fixed Figure 4: Recommended Download Procedures of EPO Files NOTE 1. Users must know the current UTC time so as to download the valid EPO files. 2. Download MD5 checksum file by replacing file extension 'DAT' with 'MD5' for checking whether the data are correct. 3. If the device is powered off for a long time, EPO files stored in flash may expire. 2.5. The Validity Period of EPO Files EPO validity period is related to the current UTC time. The EPO validity period can be obtained from the last segment of the EPO file. See Figure 1: EPO Files Format – GPS Only for the sample of how to calculate EPO validity period (GPS_Hour + 6). It is necessary to download the EPO file 12 hours in advance. The following codes show the conversion between UTC time and GPS time. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 16 / 47 GNSS Module Series void utc_to_gpstime(kal_uint32 year, //Input year kal_uint8 mon, //Input month: 1~12 kal_uint8 day, //Input day: 1~31 kal_uint8 hour, //Input hour: 0~23 kal_uint8 min, //Input Minute: 0~59 kal_uint8 sec, //Input second: 0~59 kal_int32* wn, //Output GPS week number double* tow) //Output GPS time of week { kal_int32 iYearsElapsed; //Elapsed years since 1980 kal_int32 iDaysElapsed; //Elapsed days since Jan 5/Jan 6, 1980 kal_int32 iLeapDays; //Leap days since Jan 5/Jan 6, 1980 kal_int32 i; //Number of days at the start of each month (ignore leap years). kal_uint16 doy[12] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334}; iYearsElapsed = year - 1980; i = 0; iLeapDays = 0; while (i <= iYearsElapsed) { if ((i % 100) == 20) { if ((i % 400) == 20) { iLeapDays++; } } else if ((i % 4) == 0) { iLeapDays++; } i++; } /* iLeapDays = iYearsElapsed / 4 + 1; */. if ((iYearsElapsed % 100) == 20) { if (((iYearsElapsed % 400) == 20) && (mon <= 2)) { iLeapDays--; } } else if (((iYearsElapsed % 4) == 0) && (mon <= 2)) { iLeapDays--; } iDaysElapsed = iYearsElapsed * 365 + doy[mon - 1] + day + iLeapDays - 6; //Convert time to GPS weeks and seconds. *wn = iDaysElapsed / 7; *tow = (double)(iDaysElapsed % 7) * 86400 + hour * 3600 + min * 60 + sec; } Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 17 / 47 GNSS Module Series 3 AGNSS Implementation This chapter describes two AGNSS implementation methods: Host EPO and Flash EPO. ⚫ Implement AGNSS with Host EPO The host sends EPO data to the GNSS receiver through NMEA PMTK command, such as $PMTK721. ⚫ Implement AGNSS with Flash EPO The EPO data are downloaded to the flash of GNSS receiver through Binary Protocol. Flash EPO keeps data for a longer time than Host EPO. 3.1. AGNSS with Flash EPO Flash EPO can store 7 or 14 days’ EPO assistance data on flash, which enables the receiver to make use of the available data since boot time. The communication protocol of Flash EPO is Binary Protocol. In order to download assistance data to the receiver, users first need to set the device to Binary mode through $PMTK253 so that the assistance data are downloaded in the binary format specified in this document. See Chapter 3.1.2 and Chapter 3.1.3 for details. 3.1.1. Binary Protocol The preamble of the frame, fixed as 0x04 0x24 2-byte Message 2-byte Message ID Preamble Length MsgID Payload The range for checksum calculation 1-byte The tail of the frame, Checksum fixed as 0x0D 0x0A Checksum Tail Figure 5: Structure of Binary Protocol Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 18 / 47 GNSS Module Series Table 6: Description of Binary Protocol Fields Field Preamble Length MsgID Payload Checksum Tail Length (Byte) 2 2 2 Variable 1 2 Description Fixed as 0x04 0x24. Use little endian. Total length of the messages from Preamble to Tail. Unit: byte. Maximum packet size: 256 bytes. Use little endian. Message ID. Payload data to be transferred. The checksum is the 8-bit exclusive OR of all bytes in the message between (but not including) the Preamble and the Checksum. Fixed as 0x0D 0x0A. Use little endian. 3.1.1.1. MTK_BIN_EPO (MsgID = 723) EPO binary packet is named as MTK_BIN_EPO (MsgID = 723) for convenience. Table 7: MTK_BIN_EPO Format Preamble Length MsgID 0x04 0x24 0x00E3 0x02D3 2 Bytes 2 Bytes 2 Bytes EPO SEQ 2 Bytes Payload SAT Data 72 Bytes SAT Data 72 Bytes SAT Data 72 Bytes Checksum 0x** 1 Byte Tail 0x0D 0x0A 2 Bytes An EPO file contains several SAT Data which are encapsulated in several MTK_BIN_EPO packets to be transferred to GNSS receiver. Each MTK_BIN_EPO packet contains a 2-byte EPO SEQ and 3 SAT Data fields. The length of MTK_BIN_EPO is 227 bytes. The EPO SEQ is used for synchronizing MTK_BIN_EPO packets in transfer protocol. Sometimes, there is no enough EPO data to complete the three SAT Data fields. Some of the three fields can be left as blank, that is, to be filled with 0x00. An MTK_BIN_EPO packet that only contains 0–2 SAT Data is possible and acceptable. The following three MTK_BIN_EPO packets are examples: 4.NOTE It is recommended to confirm the validity of the EPO file before sending it. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 19 / 47 GNSS Module Series Table 8: Format for MTK_BIN_EPO with 2 SAT Data Preamble Length MsgID 0x04 0x24 0x00E3 0x02D3 2 Bytes 2 Bytes 2 Bytes EPO SEQ 2 Bytes Payload SAT Data 72 Bytes SAT Data 72 Bytes 0x00 72 Bytes Checksum 0x** 1 Byte Tail 0x0D 0x0A 2 Bytes Table 9: Format for MTK_BIN_EPO with 1 SAT Data Preamble Length MsgID 0x04 0x24 0x00E3 0x02D3 2 Bytes 2 Bytes 2 Bytes EPO SEQ 2 Bytes Payload SAT Data 72 Bytes 0x00 72 Bytes 0x00 72 Bytes Checksum 0x** 1 Byte Tail 0x0D 0x0A 2 Bytes Table 10: Format for MTK_BIN_EPO with No SAT Data Preamble Length MsgID 0x04 0x24 0x00E3 0x02D3 2 Bytes 2 Bytes 2 Bytes EPO SEQ 2 Bytes Payload Checksum 0x00 0x00 0x00 0x** 72 72 72 1 Byte Bytes Bytes Bytes Tail 0x0D 0x0A 2 Bytes Table 11: Description of MTK_BIN_EPO Fields Field EPO SEQ SAT Data Length (Byte) 2 72 Description Sequence number to indicate the corresponding received MTK_BIN_EPO. Satellite EPO data. GNSS receiver will return an ACK packet for each received MTK_BIN_EPO. The packet is named as MTK_BIN_ACK_EPO (MsgID = 2) for convenience. See Chapter 3.1.1.2 for details. 3.1.1.2. MTK_BIN_ACK_EPO (Msg = 2) This packet is usually returned after receiving an MTK_BIN_EPO packet. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 20 / 47 Table 12: MTK_BIN_ACK_EPO Format Preamble Length MsgID 0x04 0x24 0x000C 0x0002 2 Bytes 2 Bytes 2 Bytes Payload EPO SEQ Result 2 Bytes 1 Byte GNSS Module Series Checksum Tail 0x** 0x0D 0x0A 1 Byte 2 Bytes Table 13: Description of MTK_BIN_ACK_EPO Fields Field EPO SEQ Result Length (Byte) 2 1 Description Sequence number to indicate the corresponding received MTK_BIN_EPO. Result. 0: Failed to receive the packet 1: Successfully received the packet Example: //Successfully received the EPO packet whose sequence number is 0x56: 0x04 0x24 0x0C 0x00 0x02 0x00 0x56 0x00 0x01 0x59 0x0D 0x0A //Failed to receive the EPO packet whose sequence number is 0x56: 0x04 0x24 0x0C 0x00 0x02 0x00 0x56 0x00 0x00 0x58 0x0D 0x0A 3.1.1.3. Change UART Format Packet (MsgID = 253) This packet changes UART communication protocol and sets baud rate. Table 14: Format for Change UART Format Packet Preamble Length 0x04 0x24 0x000E 2 Bytes 2 Bytes MsgID 0x00FD 2 Bytes Payload Protocol Baudrate 1 Byte 4 Bytes Checksum Tail 0x** 0x0D 0x0A 1 Byte 2 Bytes Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 21 / 47 GNSS Module Series Table 15: Description of Change UART Format Packet Fields Field Protocol Length (Byte) 1 Baudrate 4 Description Protocol. 0x00 = NMEA PMTK protocol 0x01 = Binary Protocol UART baud rate. 0x00000000 = Default baud rate 0x00002580 = 9600 0x00004B00 = 19200 0x00009600 = 38400 0x0000E100 = 57600 0x0001C200 = 115200 0x00038400 = 230400 0x00070800 = 460800 0x000E1000 = 921600 Use little endian. Example: //Change UART to Binary Protocol and use baud rate 115200: 0x04 0x24 0x0E 0x00 0xFD 0x00 0x01 0x00 0xC2 0x01 0x00 0x31 0x0D 0x0A //Change UART to PMTK protocol and use default baud rate: 0x04 0x24 0x0E 0x00 0xFD 0x00 0x00 0x00 0x00 0x00 0x00 0xF3 0x0D 0x0A 3.1.1.4. ACK Packet (MsgID = 1) This packet is usually returned after receiving Change UART Format Packet (MsgID = 253). Table 16: ACK Packet Format Preamble Length MsgID 0x04 0x24 0x000C 0x0001 2 Bytes 2 Bytes 2 Bytes Payload Responding MsgID Flag 2 Bytes 1 Byte Checksum Tail 0x** 0x0D 0x0A 1 Byte 2 Bytes Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 22 / 47 GNSS Module Series Table 17: Description of ACK Packet Fields Field Responding MsgID Flag Length (Byte) 2 1 Description Responding message ID. ACK flag. 0x00, 0x01: Invalid: the baud rate is invalid. 0x02: Failure: failed to set baud rate. 0x03: Success: succeeded to set baud rate. Example: //Received a valid binary packet and returned a success flag: 0x04 0x24 0x0C 0x00 0x01 0x00 0xFD 0x00 0x03 0xF3 0x0D 0x0A 3.1.2. EPO Data Transfer Protocol EPO data are packed in MTK_BIN_EPO packets and then transferred to GNSS receiver. At the beginning of the transfer procedure, the host should split the EPO files and encapsulate them into several MTK_BIN_EPO packets, then assign a sequence number starting from zero for each MTK_BIN_EPO packet to make sure the MTK_BIN_EPO packets are transferred in correct order and not missed. The host should follow the EPO Data Transfer Protocol when transferring EPO data to GNSS receiver. 3.1.2.1. Pseudo Code for EPO Data Transfer Protocol The following shows pseudo codes for EPO data transfer procedure, which are for reference only. #define MTKBIN_3EPO_PKT_LNG 227 //At first, the protocol of the communication UART is supposed to be PMTK Protocol. Since EPO data are transferred by using binary packet, the protocol should be changed to Binary Protocol. //Before starting EPO data transfer procedure, change the UART protocol set by $PMTK253. See Chapter 4.3 for the details of $PMTK253. //The SendPmtkCmd() function must be implemented by the programmer. //It is recommended to explicitly specify a baud rate when changing UART packet protocol, for example, $PMTK253,1,115200*00. SendPmtkCmd ('$PMTK253,1,0*37rn'); //Now the data transferred via the UART port will be regarded as binary packet format. Please create a thread to transmit/receive binary packets for the UART. And the thread TMtkBinCmdThread() must be implemented by the programmer. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 23 / 47 GNSS Module Series pMtkBinCmdThread() =new TMtkBinCmdThread(); //Read data in the EPO file, and then verify the validity of EPO data. If the inputted EPO file is not a valid EPO format, the programmer shall terminate the procedure. //Please check whether the file size is a multiple of 2304 bytes or 4032 bytes. //The fgEPO_Verify_File() function must be implemented by the programmer. if (!fgEPO_Verify_File (pEpoFile)) return; //Get total length of MTK_BIN_EPO packets that will be sent. //Total number=ceil ((file size/72)/3) //The i2EPO_Get_Num_Pkt function must be implemented by the programmer. i4NumSvEpoPkt = i2EPO_Get_Num_Pkt(pEpoFile); //Start EPO data transfer procedure to send EPO data. u2EpoSeq=0; u2LastEpoSeq=0; for (i = 0; iSendData(szPktData, MTKBIN_3EPO_PKT_LNG); //Update sequence number. u2LastEpoSeq = u2EpoSeq; u2EpoSeq++; } } //Generate final MTK_BIN_EPO packet to indicate the GNSS receiver that the process is finished. //The fgEPO_Get_Final_Pkt function must be implemented by the programmer. vEPO_Get_Final_Pkt(szPktData); //Send final MTK_BIN_EPO packet to the GNSS receiver. The packet size of MTK_BIN_EPO is MTKBIN_3EPO_PKT_LNG. //Then the process is finished. //The SendData function must be implemented by the programmer. pPortMtkBinThread->SendData(szPktData, MTKBIN_3EPO_PKT_LNG); //Switch UART protocol setting to PMTK packet format and change the baud rate to 115200 for the communication UART. See Chapter 3.1.1.3 for details. //The SendMtkBinCmd function must be implemented by the programmer. SendMtkBinCmd(0x04 0x24 0x0E 0x00 0xFD 0x00 0x00 0x00 0xC2 0x01 0x00 0x30 0x0D 0x0A); Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 25 / 47 3.1.3. AGNSS Procedure with Flash EPO Power on GNSS GNSS Module Series Have EPO file? NO YES Has expired EPO file? YES Erase EPO file NO Send Reference Time Download EPO files with MTK_BIN_EPO Verify downloaded data Restart GNSS Send Reference Position Position fixed Figure 6: AGNSS Procedure with Flash EPO 1. Power on the GNSS module. 2. Check whether there are EPO data in GNSS module through $PMTK607. 3. If there exists EPO data, go to the next step to check the data validity. Otherwise, download EPO data to GNSS module and verify downloaded data, then restart GNSS module and directly go to Step 6. 4. Check whether the EPO file in GNSS module has expired. 5. If not, go to next step. Otherwise, erase expired EPO file through $PMTK127 and download a new EPO file. 6. Send Reference Time to GNSS module with $PMTK740. 7. Send Reference Position to GNSS module with $PMTK741 or $PMTK713. 8. Wait for GNSS module to fix position. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 26 / 47 GNSS Module Series 3.2. AGNSS with Host EPO Host EPO allows for a simpler text-based implementation which enables the receiver to perform a fast start up where assistance data must be sent to the receiver each time it boots. When using Host EPO, the receiver can only receive one block of assistance data valid for 6 hours. Implementing Host EPO only requires a few PMTK sentences and all data transfer can be done in NMEA mode. See Chapter 4 for a detailed description of $PMTK713, $PMTK721, $PMTK740 and $PMTK741. Both Reference Time and Position can be sent through $PMTK741. 3.2.1. Recommended Sequence for Host EPO After the GNSS receiver is powered on, it will output a start-up message $PMTK010,001*2E to notify the host that it has finished initialization and is capable of receiving PMTK commands. After the host receives the system startup message, it can send the assistance data in sequence shown in the Figure 7: Recommended Sequence for Host EPO. The sequence of assistance data is Reference Time, Reference Position and EPO data. The Host EPO procedure consists of the following steps: 1. GNSS module starts up. 2. The host sends Reference Time. 3. The host sends Reference Position. 4. The host sends EPO data. The supplied Reference Time, Reference Position and EPO data must comply with the requirements listed in Chapter 1.3. NOTE In the current implementation, the host needs to wait for a $PMTK001 packet to be returned before sending another segment of EPO data. Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 27 / 47 GNSS Receiver Host EPO Sequence GNSS Module Series Host GNSS Module Powers Up Start up message Assistance Data(Time) $PMTK001(ACK) Assistance Data(Position) $PMTK001(ACK) Loop [Repeats until all EPO data are sent] EPO Assistance Data Segment 001 $PMTK001(ACK) EPO Assistance Data Segment 002 $PMTK001(ACK) The host needs to wait for $PMTK001 ACK packages Figure 7: Recommended Sequence for Host EPO 3.2.2. Sample Code of Sending EPO The following is the reference code to send one segment of EPO data to GNSS receiver. It reveals how to extract correct EPO segment from an EPO file and how to construct PMTK messages for GNSS receiver. PMTK messages for Reference Time, Reference Position, and second EPO segment are not included in this example. #include #include #define MTKEPO_SV_NUMBER 32 #define MTKEPO_RECORD_SIZE 72 #define MTKEPO_SEGMENT_NUM (30 * 4) unsigned char calc_nmea_checksum(const char* sentence) { unsigned char checksum = 0; Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 28 / 47 GNSS Module Series while (*sentence) { checksum ^= (unsigned char)*sentence++; } return checksum; } // translate UTC to GPS_Hour int utc_to_gps_hour(int iYr, int iMo, int iDay, int iHr) { int iYearsElapsed; // Years since 1980 int iDaysElapsed; // Days elapsed since Jan 6, 1980 int iLeapDays; // Leap days since Jan 6, 1980 int i; // Number of days into the year at the start of each month (ignoring leap years) const unsigned short doy[12] = {0,31,59,90,120,151,181,212,243,273,304,334}; iYearsElapsed = iYr - 1980; i = 0; iLeapDays = 0; while (i <= iYearsElapsed) { if ((i % 100) == 20) { if ((i % 400) == 20) { iLeapDays++; } } else if ((i % 4) == 0) { iLeapDays++; } i++; } if ((iYearsElapsed % 100) == 20) { if (((iYearsElapsed % 400) == 20) && (iMo <= 2)) { iLeapDays--; } } else if (((iYearsElapsed % 4) == 0) && (iMo <= 2)) { iLeapDays--; } iDaysElapsed = iYearsElapsed * 365 + (int)doy[iMo - 1] + iDay + iLeapDays - 6; // Convert time to GPS weeks and seconds return (iDaysElapsed * 24 + iHr); } void send_assistance_data(int iYr, int iMo, int iDay, int iHr) { FILE* fp; int i, segment, epo_gps_hour, current_gps_hour; unsigned epobuf[MTKEPO_RECORD_SIZE/sizeof(unsigned)]; char strbuf[200], outbuf[200]; Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 29 / 47 GNSS Module Series // open EPO file and read the header (assume EPO file has passed integrity check) if (NULL == (fp = fopen('MTKEPO.bin', 'rb'))) { return; } fread(&epo_gps_hour, 4, 1, fp); epo_gps_hour &= 0x00FFFFFF; // determine the segment to use current_gps_hour = utc_to_gps_hour(iYr, iMo, iDay, iHr); segment = (current_gps_hour - epo_gps_hour) / 6; if ((segment < 0) || (segment >= MTKEPO_SEGMENT_NUM)) { return; } // read binary EPO data and sent it to MT3339 fseek(fp, segment*(MTKEPO_RECORD_SIZE)*(MTKEPO_SV_NUMBER), SEEK_SET); for (i = 0; i < MTKEPO_SV_NUMBER; i++) { fread(epobuf, MTKEPO_RECORD_SIZE, 1, fp); // assume host system is little-endian sprintf(strbuf,'PMTK721,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X,%X', i+1, epobuf[0], epobuf[1], epobuf[2], epobuf[3], epobuf[4], epobuf[5], epobuf[6], epobuf[7], epobuf[8], epobuf[9], epobuf[10], epobuf[11], epobuf[12], epobuf[13], epobuf[14], epobuf[15], epobuf[16], epobuf[17]); sprintf(outbuf, '$%s*Xrn', strbuf, calc_nmea_checksum(strbuf)); // send them by UART // uart_send(outbuf, strlen(outbuf)); printf('%s', outbuf); // for demo } fclose(fp); } int main (void) { // get current system time // ... time(); // send assistance data of current time send_assistance_data(2009, 8, 3, 22); return 0; } Lx0&Lx6&LC86L&LG77L_AGNSS_Application_Note 30 / 47 GNSS Module

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