Digitax 4GMCU, Техническое руководство

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Odometer and OverSpeed
The AITP can keep track of the distance covered, and the real time speed, using its independent
wheel pulse input.
For that it is necessary to connect a movement sensor to the wheel pulse input.
This signal may be the same used by the taximeter, and can be connected in parallel to it.
The AITP has a 32 bits counter that counts every pulse detected, and the time elapsed, with precision
of 1/4800 seconds.
The counters may be reset by a command on the AITP Com Port. It is possible to read the counters
without modifying them, to have accumulated values, or to read & reset the counters to get
differential information.
Is also possible to let the AIPT to calculate the Speed, if the K coefficient of the vehicle is provided to
the AITP. In this case it is possible to read average speed (together with pulses and time counters,
with the same commands) or to read the current speed.
Furthermore, an Over Speed functionality can be setup in the AITP, providing a speed limit.
When the programmed speed limit is exceeded for more than 5 seconds, an Over Speed Event
message is automatically sent by the AITP to the application, in order to let them trigger an
appropriate action to the driver or the record log, and when speed is again below the limit, an Over
Speed End Event is triggered giving also the maximum speed that has been reached.
Tips for the programmer
1) Initialize GPS with the last valid coordinate
It’s very important to save the last valid coordinates received from GPS before power off, so
when the 4GMCU and the user application is started again it can initialize the GPS
ephemerides with a position that is more or less the right one. This greatly reduces the time
needed by the receiver to get the first fix, otherwise a very long fix time can occur, especially
when the car is moving.
2) Distribute properly physical RAM between Storage and Programs Memory
Physical RAM is distributed among:
Windows CE image (about 30 Mb)
Storage memory, that is all that is shown in Windows Explorer except what is on the
physical flash disks (Hard Disk, Storage Card, Hard Disk 2). For example the \Temp
memory is in the Storage memory.
Program memory, all is allocated by the application programs.
You can use SysUtils program in \SysApps folder to select how the available memory is
splitted between storage and Program memory.
3) Use the Update Folder to keep updated the System Disk
The system backup and restore feature of the 4GMCU is useful only if the System Disk is