Rojone Genius GPS (Global Positioning System)

FAQ (Frequently Asked Questions)

A1)

Please E-mail your query to engineering@rojone.com.au

A2)

The unit output can be customized to have truncated or rounded seconds.
At the present time we do not have a version that outputs data at the
same time as the 1PPS.

A3)

The start of signal processing is triggered by the 1PPS. Time to calculate
position takes about 200mS. Time to transmit NMEA messages takes about
400mS  (at 4800 baud). Including the GSV message can add another 300mS.
So the 'Total Time Difference' = 'Time to Calculate Position' + 'Time to Transmit Messages'.

A3b)

The messages based on the current nav cycles estimate of UTC will go on to
the serial port approximately .5 - .7 seconds after the 1 pps.  The UTC will
be plus or minus 1 ms of the time of the pulse.  For example if the first
message after the pulse says xx:xx:58.999 then the pulse is for
xx:xx:59.000.  The message may be delayed in internal or external buffering
systems.  If raw track is on or the baud rate is low the message could be
delayed in our internal buffers past the next 1 pps pulse.  If you watching
sirfdemo for time then windows also delays getting the data to the screen.

A4)

You have identified a known problem with Version 132ROJN101b software.
This software operates correctly while battery back-up is maintained or when the
reset pin is activated following powerup.

After the internal power has discharged, the unit uses an alternate initialization routine
that bypasses our hardware switch test.

This problem is scheduled to be fixed in March 2000.

A5)

The Reset input has an internal 20k pull-up resistor, so it can be left open if it is not used.
If Reset is driven from long cables or if the device is used in a noisy environment, connecting a
0.1µF capacitor from Reset to ground provides additional noise immunity.

A6)

The attached latest release, Version 1.3.2Dkit344 software is intended to accompany all future Evaluation Kit shipments. This software replaces 1.3.1Dkit144 software for all HitachiTM CPU based customers. The 1.3.2 software maintains all  the enhanced features of  previous releases,  performance capabilities and low-power management. In addition, the software now supports up to 4 bi-directional serial ports for data I/O (only two supported on the Evaluation Kit module), which allows the user to output SiRF binary and NMEA protocols simultaneously or either protocol with RTCM correction input.

Change Description (1.3.1Dkit144 to 1.3.2Dkit344)
 Several improvements to the software in this release have been made to address reported field issues and to implement some additional system features.

Improvements to Software Release.

1) Trickle-Power (TP) start up: Previously, at start up, if the system was set in TP mode and failed to acquire any GPS signals, it would stop searching in 2 minutes and would not make any additional attempts. The receiver will now continue to search for satellites for the same 2 minute period ( in the absence of GPS signals) and  then will revert to the Off Time as specified by the Duty Cycle. Once the Off  Time has been satisfied, the receiver will re-attempt signal acquisition  and navigation. If no signals are available, then the receiver will return to sleep mode and attempt later.

Example:  TP settings of 200 ms On Time, 1 seconds update rate = 20% duty cycle.
  Search time is 2 minutes , Off Time is 8 minutes and cycle is repeated.

2) Power on Reset: Receiver designs using the Hitachi CPU were subject to a potential failure at start up. When power was supplied to the board it would fail to start with recovery achieved only by activating the reset button. The 1.3.2 software in combination with the new boot1.s file and recommended hardware changes (Rev. D) alleviates this issue.  Please contact SiRF sales for a boot update and hardware modification instructions.

3) Startup Navigation Failure: In regions of high obscuration, where it can be very difficult to start up, there was the possibility of the navigation filter resetting after prolonged attempt to navigate (repetitive Krause solutions) causing the position, velocity and time output  to be all zeros and never attempt navigation until a system reset. This has been fixed such that the system will continue to attempt navigation until a satisfactory solution can be attained.

4) TricklePower I/O: The very nature of TricklePower causes CPU shut down and can impede serial input. A mechanism has been put in place to communicate the status of CPU on/off conditions to the user application (i.e. SiRFdemo).  Additional buffering of messages by both 1.3.2 and SiRFdemo significantly enhances the communication capabilities between the systems.

** NOTE **   This feature is not supported in NMEA as this protocol is output only.

New System Features

1) 4 Port Functionality: 1.3.2 now supports up to 4 bi-directional serial ports for simultaneous data I/O (2 ASIC and 2 CPU). The user can now output up to 4 uniquely defined protocols or input RTCM DGPS corrections on any port.  Currently, all system communication must be done via SiRF Binary protocol. If NMEA is the only output protocol, the user may issue the “Switch to SiRF Binary”  NMEA  command and restore complete system command capability. See the addendum to the SiRFstarI/LX Users Guide for more details.

** NOTE **  Trickle-Power support is only allowable when the CPU ports enabled.

2) GPS Week Reporting: On Aug, 22, 1999, the GPS week rolled over from 1023 to 0  in accordance with the ICD-GPS-200 specifications. To maintain roll over compliance, SiRF reports the ICD-GPS week between 0 and 1023 in messages 002 and 004. If the user needs to have access to the Extended GPS week (ICD GPS week + 1024) this information is available via the “Clock Status Message” (007) under the “Poll “ menu.
 Software Tools

1) SiRFdemo: Version 2.3.12 has been updated to support all changes to the receiver software.  An addendum to the SiRFstarI/LX User’s Guide is being provided.

** NOTE **  SiRFdemo is a general application tool that operates with all SiRF product lines. Where applicable, some features are unique to a certain product (i.e. SiRFstar II)  and may not available for the SiRFstarI design.

2) SiRFprog: Version 1.6 is the new code loader for all SiRF product lines. It has been converted to a win95/98/NT platform for ease of use and increased reliability of updating receiver code. See the SiRFstarI/LX addendum for details on software operation.

Reminders of Software Settings

DOP Mask
The default setting for the 1.3.2 software is NO DOP MASK. This implies that positions computed under poor satellite geometric conditions (<50)  will be reported as valid.  There is a SiRF protocol receiver command for setting DOP mask values and type that will allow positioning filtering based on DOP to be implemented. The SiRF version of the Kalman Filter will absorb the effects of poor geometry for a short duration and maintain a smooth trajectory during transition periods in changing conditions. Many systems will activate a DOP mask to ensure position accuracy (i.e. reject all positions with a DOP > 10). The use of a DOP mask can effect position density in applications where severe blockages may occur (i.e., urban canyon) and is generally a good indicator of possible position error.

NMEA Protocol in  TricklePower mode
The NMEA standard is generally used in continuous update mode at some predefined rate. This mode is perfectly compatible with all SiRF Trickle-Power and Push–to-Fix modes of operations.  There is NO mechanism in NMEA that indicates to a host application when the receiver is on or in standby mode. If the receiver is in standby mode (chip set OFF, CPU in standby),  then no serial communication is possible for output of NMEA data or receiving  SiRF proprietary NMEA input commands. In order to establish reliable communication, the user must repower the receiver and send commands while the unit is in full-power mode (during start-up) and prior to reverting to TricklePower operation. Alternatively, the host application could send commands (i.e. poll for position) repeatedly until the request has been completed.  The capability to create communication synchronization messages in NMEA mode  is available via the System Development Kit (SDK).

In Trickle-Power mode, the user is required to select an update rate (seconds between data output) and On Time (milli-seconds the chipset is on). When the user changes to NMEA mode, the option to set the output rate for each of the selected NMEA messages is required. These values will be multiplied by the TricklePower update rate value. See the Table 2 for examples.
 

Table 1 - NMEA DATA RATES UNDER TRICKLE POWER OPERATION
 

Power Mode         Update Rate         On Time         NMEA Update Rate         Message Output Rate
Continuous         1 every second     1000             1 every second                     1 every second
Trickle Power     1 every second     200             1 every 5 seconds                 1 every 5 seconds
Trickle Power     1 every 5 seconds 400             1 every 2 seconds                 1 every 10 seconds
Trickle Power     1 every 8 seconds 600             1 every 5 seconds                 1 every 40 seconds
 

**NOTE **  The On Time of the chip set has no effect on the output data rates.
 

TricklePower Operation in DGPS Mode

The TricklePower mode of operation DOES NOT yet support the use of Differential GPS corrections. In TricklePower mode, the CPU is put in standby mode and all serial port communications are lost. While there is message synchronization (SiRF protocol only), there is no capability to fully receive externally generated  asynchronous messages (i.e. RTMC from the Coast guard).

A7) It is important to differentiate between the phase noise of the
crystal and the phase noise of the GPS delta range measurements.  I am
attaching the crystal spec for the former, but for the latter, watch out!
Anyone who asks that is trying to use the GPS for ultra high accuracy
surveying stuff (often called RTK) and we dont really support that yet.  In
theory, our measurements are as good as anyone elses but we have never tried
to use our board to replace the $1000 rovers used for RTK.
 
 

Q8) I tried to send a message like:
$PSRF103,00,00,03,00*26 <CR><LF>
but got no response. This was from a terminal program (an excellent one)
during the incoming strings bombarding the terminal screen.

A8) I have found a way to force windows hyperterminal to transmit NMEA.
This terminal translates the <CR><LF> to <CR><CR>. It will work if
 you paste the string "$PSRF103,00,00,03,00*26", then  press the <CTRL-M> key then press <CTRL-J>.

Note: The correct Checksum is REQUIRED for all communication to the genius. The checksum is
simply an XOR of all characters up to the '*'. The two digit hex result is added to the end.
 
 
 

Q9) A question. Does this then remain the default? Is there a "save and exit"
string? When I was playing with sirF demo, I was able to change to GGA per
3 Secs but it resorted to the original default at power up.
As I am a power junkie, I would like to know that I could change and store
as default even though you will be supplying our current needs as default.

A9) The 'default' state is compiled into the program and can not be
altered by software. The program may be upgraded across the serial
port into the Genius flash memory.
However, software settings may be changed and maintained
as long as 3V battery backup is supplied to the SRAM.
The on-board capacitance can typically hold the previously selected
settings for several hours. So I can use sirfdemo to select NMEA GGA 5 seconds,
(just doing it now to make sure :) ok, switch the unit of, unplug it,
now, wait 60 seconds... plug it back in, and yes, it has retained this
setting.
 
 
 
 
 
 

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