Table of contents
3.Introduction
4.Specification requirements
5.Solutions suggestions
6.The magnetic fields sensors
7.The inclination measurement system
8.The gyroscope
9.The data acquisition system
10.Communication system
11.The power supply
12.Realisation of the PCB
13.The embedded system
14.Static Library Util.a
15.ViewPort
16.Xcompass
17.Sensors controller commands
18.Test
19.Future improvements
20.Conclusion
21.References

13.           The embedded system

The embedded system on the Smart Compass controller is written in C-language. That program manages the different the instrument compute the data received from the ADCs.

13.1.                System overview

The main entry of the program is the file ‘main.c’. Three methods are implemented in this file:

• 'main ()' that is the entry point of the program and realise the main routine. It initializes the different modules of the system.

• 'welcome_msg ()' returns information about the Smart Compass card and the program version, the date of development, the authors and supervisor.

• 'version_exec ()' return the actual version of the program.

• 'parse_command ()' execute the instruction send by Xcompass or viewport through the RS232 or RS485 connection. The command and the parameter available that composed this instruction declared in the identical way in the driver.

When the microcontroller boot, it initializes the different module and prints the welcome message. At that point, it will wait until an instruction is addressed to the smart compass card.

13.2.                The program comm and timer

The two C-program ‘timer’ and ‘comm’ are inspired from the UAV embedded system. The program ‘timer.c’ contains the different methods that manage the delay or the different interrupt mode. We have reused these timer functions without modifications.

The file ‘comm.c’ contains the different method to communicate throw the serial or the SPI port. It contains in particular the functions to initialize and to use the UART:

The printf() function is enabled by the init and extra method have been implemented to directly send and receive the instruction structure.

In addition, we have added three methods that initialize and read values on the two different ADC: the function ‘adc_atmega32’ and ‘adc_max186’. These methods have been developed to work on both the card. The number of the card is defined in the header of this program.

Any bit received by the RS232 (or RS485) will raise an interrupt that will store the request. If the length of the request corresponds to the length’s value given by the instruction, the command is parsed.

13.3.                The module’s program

If the command is one of the five modules of the compass (MAGNETO, GYRO, ACC, REF_VOLTAGE, or COMPENSATION), the parameter is redirected to the corresponding module application:

                Figure 25

Note: The COMPENSATION module has been included on the file ‘magneto’ as it concerns the compensation of the magneto module and it does not require an independent file.

The other available commands are considered like the informational command (VERSION, CARD, USAGE, and PING).

The different programs that process the modules have the common method according to the available parameter (see section 17.2.2):

Each module’s program has a method '[ModuleName]_exec' that interpret the parameter’s value.

If this value corresponds to MODULE, the method 'module_[ModuleName]' is executed. It returns all the output values available for that module.

If the parameter’s value is ANGLE, the calculated value of the azimuth is returned.

13.4.                The power switch

If the supply voltage is sufficient, the second DC/DC converter can be switch off. On the first card, this is done by a hardware control. However, on the second card, the control is soft. The selection can be set on manual or automatic.

To this purpose, we have three available modes that can be executed by the method ‘power_switch’:

• ON: enable manually the DC/DC converter (SMR)

• OFF: disable manually the DC/DC converter (MMR)

• AUTO: enable automatically the converter if the supply power is inferior to 18V

13.5.                The magneto pulse      

To realize a pulse command, we have to generate first a SET and then a RESET signal. The pulse circuit is connected on the port PC0 (SET) and PC1 (RESET) of the microcontroller. A pulse can be generated by a software method (‘magneto_pulse’) with  in argument the kind of signal that we want to generate:

• For a SET signal: first PC0 = 1 then PC1 = 0

• For a RESET signal: first PC0 = 0 then PC1 = 1

The magnitude of the field on each axis is difference between the values read after a Set a Reset. This value can then been pass to the method ‘magneto_get_north’ that will return the azimuth.

13.6.                The magneto compensation

The module compensation can generate an opposite magnetic field to eliminate the magnetic interference. This module controls the value of the curser in the digital potentiometer, which drive the compensated field.

Similarly to the other modules, when the command COMPENSATION is executed, the method ‘compensation_exec’ switch the first parameter. This last one corresponds to the axis of the magneto sensors to compensate. The second parameter corresponds to the compensation’s value. These two parameters are passed in argument on the function ‘magneto_compensation’ that realize this operation and returns the value VALID to confirm the compensation.