6 GPIO 84. Date: 29/09/2016 Name: ID: This laboratory session discusses about writing program to interact with GPIO of Reapberry Pi.

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1 6 GPIO 84 Date: 29/09/2016 Name: ID: Name: ID: 6 GPIO This laboratory session discusses about writing program to interact with GPIO of Reapberry Pi. GPIO programming with Assembly Code:block installation GPIO programming with C 6.1 Raspberry Pi s GPIO Pins GPIO stands for general purpose input/output. These pins can be used to connect external electronic devices to the Raspberry Pi. This also allows the users to build their own circuits and control them using software written in languages such as Assembly, C or Python. The GPIO pins can be divided into a number of categories, i.e. Standard GPIO I2C Serial Rx and Tx SPI PWM and PPM The following figure illustrates the GPIO pins of Raspberry Pi 3 model B.

2 6 GPIO 85 Figure 6.1: Raspberry Pi GPIO layout - Pi 3 Model B Standard GPIO The standard GPIO pins provide an interface for other electronic devices which can be either controlled or read data from. These pins can be configured as output or input. One important things to note is the numbering format. There are two different ways in which we can refer to the pins, via the GPIO number or the physical numbering. The GPIO numbering (also known as BCM) is the method by which the Broadcam chip see them. The detail of these numbering format can be found at When writing applications, you will need to know these BCM pin numbers in order to switch them between modes. The second methodology for listing the pins is by their physical position. (see Figure 6.1). This maps the physical pin location to the pin type. It should be noticed from this figure that a number of the pins are power pins with specific voltage. (3.3V and 5V) With the Raspberry Pi, it must be aware of the voltages used. The GPIO banks

3 6 GPIO 86 all use a voltage of 3.3V. It is important to understand that applying a voltage higher than this to the pins will seriously damange your device. The pins can be set to OFF,LOW and HIGH. Among the Raspberry Pi GPIO pins, you will also find two 3.3V pins and two 5V pins, and several ground pins. This can be used to powering other devices attached to your Raspberry Pi, either through a breadboard or via the GPIO headers directly I2C The I2C standard is used to allow one microchip to talk to another. The Raspberry Pi supports I2C using pin 3 and pin 5. With help of I2C, we can connect multiple devices to the Raspberry Pi and assign each a unique address Serial Rx and Tx The Rx and Tx pins are responsible for serial communication. Serial communication is the process of sending data one bit at a time in sequence over a communication mediu. Typically these ports can be used for console input and output. Thus another serial device can be connected to the Raspberry Pi and the serial data read and display to the user, allowin them to debug problems SPI Serial Peripheral Interface (SPI) is a bus designed for synchronous serial communication. It is useful for communicating between peripheral devices quickly over short distances. The Raspberry Pi comes with a single SPI bus that has two chip selects. This bus can be interacted with via the SPI pins on the P1 header. By default, the SPI master drive is disabled, but it can be enabled via the command raspi -config

4 6 GPIO PWM and PPM PWM stands for Pulse Width Modulation. This methodology can be used to control the amount of power sent to an electrical motor, thus controlling its speed. The principle behind this is the implementation of a square wave. It is possible to generate a software-based PWM square wave using any of the standard GPIO pins. The wiringpi library comes equipped with instructions on how to achieve this. PPM stands for Pulse Position Modulation and is popularly implemented for servos. Servos short for servomechanisms are type of electrical component, such as motor, that uses error sensing negative performance to correct its position Hardware Setup for Blink LED 1. Prepare the following components: An LED (given) Aresistor(given) Breadboard Wires 2. TURN OFF the power of the Raspberry Pi 3. Take a wire and connect one end to a ground GPIO pin on the Raspberry Pi. The other end of the wire shall be connected to a hole on the ground rail on the breadboard as shown in Figure 6.2. (Note that you may have additional connector in between) 4. Take an LED. Note that one leg is longer than the other. 5. Put the LED into the breadboard. Be sure that its legs are not connected to each other. (See Figure 6.3) 6. Locate a given resistor and connect one leg to the ground rail and the other leg to the shorter leg of LED. (see Figure 6.4) 7. Complete the circuit by connecting a wire to pin 1 on the Raspberry Pi. (see Figure 6.5) Instructor s signature

5 6 GPIO 88 Figure 6.2: Connecting Ground 8. Turn on the power of the raspberyy Pi. Observe and record the result. 9. Locate TWO other different ground pins of Raspberry Pi which can be connected to the LED and obtain similar result

6 6 GPIO 89 Figure 6.3: Put LED on breadboard 10. Why one shall include a resistor to the circuit? Instructor s signature

7 6 GPIO 90 Figure 6.4: Connecting the resistor 6.2 WiringPi Library WiringPi is a GPIO access library written in C for the BCM2835 used in the Raspberry Pi. It is released under the GNU LGPLv3 license and is usable from C and C++ and many other languages with suitable wrappers. WiringPi includes a command-line utility gpio which can be used to program and setup the GPIO pins. You can use this to read and write the pins and even use it to control them from shell scripts. WiringPi uses its own pin numbering scheme as shown in Figure 6.6 The figure shows how WiringPi numbers your GPIO pins.

8 6 GPIO 91 Figure 6.5: Complete the circuit 6.3 Blink LED with Assembly 1. Navigate to the directory /home/pi/assemblylabs 2. Create a new directory using command mkdir -p Lab6/assembly 3. Navigate to the directory /home/pi/assemblylabs/lab6/assembly 4. Type in pwd command and be assure that you are on the directory /home/pi/assemblylabs/lab6/assembly 5. Create a new assembly file name Lab6.s using vim 6. Enter Insert mode and put in the code as shown in the following: (Comments can be left out.)

9 6 GPIO 92 Figure 6.6: Mapping of WiringPi and Data 4 Intro:.asciz "Raspberry Pi wiringpi blink test\n" ErrMsg:.asciz "Setup didn t work... Aborting...\n" pin:.int 7 i:.int 0 delayms:.int 250 OUTPUT =

10 6 GPIO Code main.extern printf.extern wiringpisetup.extern delay.extern digitalwrite.extern pinmode main: PUSH {ip, push return address + dummy for printf( "blink..." ) ; LDR R0, =Intro BL if (wiringpisetup() == -1) printf( "Setup didn t work... Aborting." ) exit (1) } BL wiringpisetup MOV R1,#-1 CMP R0, R1 BNE init LDR R0, =ErrMsg BL printf B pinmode(pin, OUTPUT) ; init: LDR R0, =pin LDR R0, [R0] MOV R1, #OUTPUT BL for ( i=0; i<10; i++ ) { LDR R4, =i LDR R4, [R4] MOV R5, #10 forloop:

11 6 GPIO 94 CMP BGT R4, R5 digitalwrite(pin, 1) ; LDR R0, =pin LDR R0, [R0] MOV R1, #1 BL delay(250) ; LDR R0, =delayms LDR R0, [R0] BL digitalwrite(pin, 0) ; LDR R0, =pin LDR R0, [R0] MOV R1, #0 BL delay(250) ; LDR R0, =delayms LDR R0, [R0] BL delay ADD R4, #1 B forloop done: POP {ip, pop return address into pc 7. Run the program by typing the following commands: as -o Lab6.o Lab6.s gcc -o Lab6 Lab6.o -lwiringpi sudo./lab6

12 6 GPIO Observe and record the result. Instructor s signature

13 6 GPIO Working with Code::Blocks 1. To install Code::Blocks IDE, type in the following command at the command prompt sudo apt-get install codeblocks Note that you do need internat connection to download and install the software package 2. To start the Code::Blocks IDE, type in the following command sudo codeblocks This will give Code::Blocks access level to be as superuser. 3. The first time you launch Code::Blocks IDE, it will ask to confirm the compiler plug-ins. Unleass you have installed other compiler tools, it should detect only the GNU GCC compiler. 4. After the IDE is launched, it displays the Start here window. Click on Create a new project link and a window with the title New from template pops up. 5. Keep the default wizard type as Project and click select Console application wizard and then click the Go button. (See Figure 6.7) 6. The window will be replaced by Console application wizard. 7. It will ask for the selection of programming language. Select C then click Next> button. (See Figure 6.8) 8. The next window asks for the project title and the folder where the project will be created. The wizard creats a folder with the project name under the folder you specified and put all the project files and folders in it. Figure 6.9 show that the folder /home/pi/asm and project title p2_1 is created 9. Create the project name Lab6 under the folder /home/pi/assemblylabs/c 10. Click Next> button and the next window is used to select compiler and configuration. Take the default selection as shown in Figure 7.4 then click Finish button.

14 6 GPIO 97 Figure 6.7: New project using Console application wizard 6.5 Blink LED with C 1. Open project Lab6 2. Go to Setting/Compiler.... The Global Compiler Setting will show up. 3. Go to tab Linker settings and click Add button. 4. Enter /usr/lib/libwiringpi.so; to the Add Library window. Then click OK button to close the window. 5. Click OK button to finish. 6. Enter the following code in main.c #include <wiringpi.h> #include <stdio.h> #include <stdlib.h> int main ( void ) {

15 6 GPIO 98 Figure 6.8: SelectingClanguagefortheproject Figure 6.9: Specifyprojectfolderlocation int pin = 7; printf("raspberry Pi wiringpi blink test\n"); if (wiringpisetup() == -1) {

16 6 GPIO 99 Figure 6.10: Specifyprojectfolderlocation } printf( "Setup didn t work... Aborting." ); exit (1); pinmode(pin, OUTPUT); int i; for ( i=0; i<10; i++ ) { digitalwrite(pin, 1); delay(250); } digitalwrite(pin, 0); delay(250); } return 0; 7. Observe and record the result.

17 6 GPIO 100 Instructor s signature 6.6 Assignments 1. Connect three LEDs to the Raspberry Pi. (see the WiringPi pin configurations). Write a C program such that the three LEDs show binary number counting from 0-7. Instructor s signature