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

17.            Sensors controller commands:

The communication between the PC and the robot consists to a set of commands and parameters. The PC sends different instructions to the navigation’s system that interpret the command and the parameter. Consequently, these instructions have been implemented both on the microcontroller and on the driver.

17.1.                The commands frame

The request sequence sent to the Atmega32 follows syntax:

Request
Reply

Figure 37: command frame

17.2.                The request

It consists in two enumerations: command and parameter.

We have the following correspondence between the commands, the parameters and their numbers:

Table 13: The commands and parameters available

The first value off the enumeration ‘COMMAND’ and ‘PARAMETER’ are respectively ‘NO_COMMAND’ and ‘NO_PARAMETER’. Of ‘NO_COMMAND’ is never used on the program, but this declaration allows forbid the utilisation of the value ‘0’ for the command. Therefore, it is always interpreted like an error.

The main commands are the five next. They are required to the calculation of the magnetic north.

The instruction set sends from the computer to the Smart Compass card is composed by two bytes:

17.2.1.  The headers:

• The length of the instruction on the four most significant bytes

• The device ID of the card on the four lower significant bytes (the device id is 10 for the electromagnetic compass)

The headers are used to control the request. When the system receives an instruction, it first checks if the instruction is for it (with the device ID) and if the no loose of data occurs during the transmission (with the length). If these two conditions are true, the command is interpreted

17.2.2.  Command and parameter

According to the command and the parameter received, it returned one or more values. To obtain these values the commands and his parameter should belong to one of these combinations:

Table 14: instruction set

These previous instructions are available for the two cards.

Except the two combination: ‘POWER_SUPPLY’ / ‘REF_VOLTAGE’ And ‘MAGNETO’ / ‘ANGLE’

In addition, the command ‘COMPENSATION’ has two parameters instead of one for the other command. Consequently the length of this instruction is 3 bytes. The first parameter is used to select the axis of the magneto to compensate and the second contains the value of the compensation.

The command ‘GET_ALL_SENSORS’ is not really a command because it is not directly sent to the MCU. It is just use to address all the sensors.

The commands ‘VERSION’, ‘USAGE’ and ‘CARD’ are implemented to get information about the navigation’s system card.

17.2.3.  Example of instruction:

            To know the voltage value on the magneto’s z-axis, you should send the following bytes:

                        0x2A   0x16

The hexadecimal value:

• 2 corresponds to the length of the instruction

• A to the device ID

• 1 to the magneto module

• 6 to the parameter z-axis

17.3.                The reply

The response returned by the navigation system match the structure on Figure 37.

17.3.1.  The return code

The validity of the instruction is indicated by the fourth byte: the return code. The different control values are the following ones:

Table 15: Return Code

The three first values on the Table 15 correspond to a valid value the other means that an error happens. CONFIRM_REBOOT is returned in the data to confirm the reboot and PONG that the connection with the system is established. Except these two cases, if the fourth byte is different to VALID, we will have one of the other possible values.

All the replied from the smart compass are finished by the character “\0” that signify the end of the data. It allows to check the length of the response and therefore if there were no loss during the transmission. The device ID allows checking the source of the response.

Most of the data returned by the card are in short format, except for the ANGLE and the VERSION, where the size is in double format (4 octets).

17.3.2.  Example of reply:

The kind of response that we can obtain for the request of the previous example could be:

            0x06    0x0A   0x16    0x0F    0x07    0x0D

This will correspond to:

• 06 corresponds to the length of the reply

• 0A to the device ID

• 1 to the magneto module

• 6 to the parameter z-axis

• 0F to VALID

• 070D to the value: 1805

To send automatically a command to the system you just use the command method in the CModule class. Still for the previous example, you can do the following instruction:

unsigned short data = 0;
Navigation->commands(
MAGNETO,   // module
Z_AXIS,     // parameter
data,       // pointer to receive the data
sizeof(data) // format of the waited data
);

All the types of format are accepted by this method. You can pass for example the pointer on a structure of unsigned short to receive more than one octet.