moway Exercise The C Programming Language

Transcription

1 moway Exercise The C Programming Language 1

2 Index Introduction... 2 C Language... 3 moway libraries... 3 moway bootloader... 4 Create a project... 4 Main Program... 9 Recording of the Program

3 Introduction The functioning of moway is based on a microprocessor. This electronic device has the ability to control the robot's elements (motors, sensors, LEDs, etc.) through a program stored in its memory. moway can be programmed both graphically (using flowcharts) and in C language (written code). For those who are not familiar with programming, the best way to start working with moway is with graphical programming. Once the basic concepts of programming are grasped, you can carry on with your learning using the C programming language. C language serves as a basis for many other programming languages and, for that reason, understanding C basics is useful to start programming in another language. On the other hand, using written code provides a higher flexibility for the design of our program. Also, the generated programs are faster and more efficient. The table below compares graphical programming and C programming: Graphic programming Programming with C code Simple Learning basic concepts of programming Intuitive language Flexible and adaptable Learning advanced concepts of programming Widely used language For this exercise, we are going to explain how to create a C language project to program moway. It will be used in the MPLAB Environment with all necessary configurations to create a sample program. 2

4 C Language C language is based on functions. In the case of moway, the functions are instructions to control the robot, such as going forward, turning on a LED, etc. The functions of moway will enable us to easily access its sensors and actuators with a single line of code. As we shall see later, these functions are defined in libraries. Next, a sample program in flowcharts and in code is shown below: moway libraries Controlling the elements of moway (motors, actuators and sensors) would require some knowledge of electronics, since these elements are activated through specific electrical signs, which are activated through the microprocessor. Instead, libraries of moway have been created to simplify this task. The libraries are pieces of prepared code that the user can make use of. Therefore, it is possible to control the different elements of the robot with a single code line, without requiring any knowledge of the internal electronics of the robot. You may find on the moway Website and in the installation package the libraries to use the sensors, the motors, the RF module and the camera. 3

5 moway bootloader Code programmed on moway is stored in its microprocessor, in its program memory. This memory of the microprocessor is divided into two parts: The main program, which is the one we have designed and programmed in moway. For example, a program that moves forward and turns on the front LED. Bootloader The bootloader, a small program that communicates the robot with the computer via USB connection. Main Program IMPORTANT: the bootloader should always be in the memory of the microprocessor. Without it, it would be impossible to record the robot via the USB. Therefore, when you design your own program you must not overwrite it. This is achieved by "jumping" the memory locations of the bootloader (in the "upper" part of the program memory). The necessary steps to achieve this are explained later. Create a project In order to create a program in C language, it is possible to use the MPLAB Environment, developed by Microchip. Download a free version from the site ( Before you create a project, you must install all the elements of the C18 compiler. These elements are integrated into the MPLAB environment. The next example was created with the MPLAB 8.4. To create our first project, the Project Wizard of MPLAB will be used, which enables to create projects quickly. 4

6 1. Once the MPLAB is open, you must start the Wizard Project from the tool bar: Project -> Project Wizard 2. We will begin by selecting the microprocessor installed in moway. Depending on the robot version, the microprocessor will be either PIC18F86J50 (version 2.0.1) or PIC18F87J50 (version 2.0.2): 5

7 NOTE: the version of the microprocessor can be viewed in the lower corner of MowayGUI and MowayWorld. 3. Next, you must select the MPLAB C18 C Compiler tool: 6

8 4. Then, you must indicate the location of the project you are about to create, as well as its name. For this example, the project will be named "moway_first_project": 5. The next step is to add the moway libraries to the project, which control the elements of the robot (motors, sensors, etc.). It is suitable for the route of these libraries to be the same as the one of the project, that is, that they are stored in the same folder. 7

9 Upon completion of these steps, you will have created a project with the build tools and the libraries indicated above. Now you need to add the code file where the main program is to be written. 1. Create a new file (New File) and save it in the same project folder with the name main.c. This will be our main program. 8

10 2. Add the source file (the one you have just created) to the project, going to Project Add Files to Project Similarly, add the linker script of moway ( Moway_lnk.lnk ). This file specifies the memory addresses assigned to record the program. In summary, the files needed to compile this program are explained below: Source files: o "main.c": contains the main programmed. Header files: o "delays.h": contains the pause functions. o "lib_mot_moway.h": contains the movement functions for the motors. o "lib_sen_moway.h": contains the functions to read sensors and activate lights. o P18f86j50.h : contains the definitions of the microprocessor. Linker Script: o Moway_lkr.lkr : assigns the memory addresses to the program. Main Program Let's take a simple example of programming in C language. Once the project has been created as seen above, we start to edit the file main.c defining the libraries. The library p18f86j50.h is included in all moway projects, because it contains the definitions of the microprocessor of the robot. Besides, the motors and LED have been used for this example. The code for motors is defined in the library lib_mot_moway.h. The code for activate sensors and LEDs is defined in the library lib_sen_moway.h. After that, define the reset vector. The reset vector is the memory location where the program will start when moway turns on. This position is 0x1000, just after the bootloader. IMPORTANT: This code is necessary to avoid overwriting the bootloader with our main program. 9

11 Then, the main program starts ( main function). This program contains the data of the actions to be performed by the robot. The first task is to configure the motors ( MOT_CONFIG ), the sensors and the LEDs of moway ( SEN_CONFIG ). To complete the program, we make the robot wait one second. Then we make it turn on the front light and to move forward for 1 second. The program ends in an empty endless loop (instruction "while(1)"). NOTE: an endless loop is added because the microprocessor needs to be issuing nonstop instructions. As in this case we need to repeat no action, there is no instruction in this loop. 10

12 Once we have finished the code, it is time to compile it. Compiling means converting the code we have written into a "language" that the robot is able to "understand". When compiling it, a file with the ".hex" extension is created. This file is the one we are going to record on the robot. 1. To compile the project, press the icon shown in the image below: 11

13 2. After a few seconds, a message will be displayed announcing that the compilation was correct: Recording of the Program Once the compilation with MPLAB is done, a file is created inside the project folder with the project name and the ".hex" extension; in this case, "moway_first_project.hex". This is the file we will be using to program our robot. 12

14 Next, we record the ".hex" file created from MowayGUI or MowayWorld, selecting the route where we have saved the project "moway_first_project": The robot will be automatically programmed with the program we have just written in C language. The sequence of images below shows the result of this program. 13