DevelGPS [Stellaris]

The purpose of this project is to implement a portable GPS locator / geocaching finder with the Cortex-M3 based Luminary Micro LM3S1968 evaluation board.

The device proposes a user interface to configure the GPS coordinates of a target location and shows on the OLED display the direction and distance to reach the target.

Hardware requirements

• Luminary Micro LM3S1968 Evaluation Kit;
• a GPS module;
• a mobile phone battery.

Software requirements

BeRTOS components used for this project:

• Kernel with preemptive scheduler and task priorities;
• Device drivers: UART, OLED display, navigation/select pushbuttons;
• NMEA parser;
• GFX library (+ menu management module).

Implementation

The GPS module is connected to UART1 RX pin (UART0 is kept for debugging purposes). The mobile phone batter is used as a power source both for the GPS module and the LM3S1968 board.

From the software's point of view, BeRTOS already provides the drivers to manage all the required devices and a NMEA parser to retrieve the right informations from the raw GPS strings: position, date & time, link quality.

The multi-process environment and preemptive scheduler provided by BeRTOS is exploited to create independent threads operating in producer/consumer way:

• a thread takes care of retrieving and processing NMEA string from the UART;
• a thread manages the GUI, updating the OLED display on new GPS informations or user's input;
• a thread reports the status of the GPS receiver blinking a LED when GPS data are correctly received.

The GUI is organized using a main menu that allows to select:

• a form to insert the target GPS coordinates;
• a form showing a compass with target direction, distance and GPS positions to reach the target;
• a form to show the status of the GPS receiver.

BeRTOS has a builtin graphics module.

BeRTOS text management facilities ease development process.

NOTE: the distance is evaluated using the Haversine formula between the current and target GPS position. The Haversine formula remains particularly well-conditioned for numerical computation even at small distances, making the device particularly useful when walking, hiking or moving at a close distance to the target.