Lab 6: Design of a Digital Customer Counter using GPIO Interrupt
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1. UNIVERSITY OF Electrical and Computer Engineering I SASKATCHEWAN CME 331 Microprocessor Embedded System Khan Wahid Last updated November 21 2013 Lab 6 Design of a Digital Customer Counter using GPIO Interrupt and LCD Display Safety In this lab voltages used are less than 15 volts and this is not normally dangerous to humans However you should assemble or modify a circuit when power is disconnected and do not touch a live circuit if you have a cut or break in the skin Learning outcome This lab provides an opportunity to learn a multiple interrupt handling in an ARM CortexM4F microcontroller and b proper configuration to use GPIO external interrupt The lab uses a TFT LCD display At the end of the lab the students will be able to design an interrupt based digital display system for a shop that displays the number of customers present at a given time Required hardware Checkpoints Throughout this manual wherever you find a STOP sign it means that there is something that you need to a show to your instructor and or b observe measure and explain in your lab notebook Lab description In this lab you will design a digital display and warning system of a store The system displays the total customer capacity of the store which is 30 and the total number of customer inside the store at a given time on the TFT LCD display 4 If the number of customer is 30 or more the system will change the display color to r2. S pPE2 PD6 PA4 PA6 PE3 PD7 PA3 PAT PFI PF4 PA2 Fig x Header pins on the LaunchPad EK LM4F120XL END
3. al operation right flashing warning in red Obtain from the support office the required hardware for the lab Connect the LCD display with the LaunchPad The connection diagram is given in Fig 1 LM4F120 LaunchPad 3 3V PA2 SSIOCIk PA5 SSIOTx PA3 SSIOFss PA6 PA7 3 3V GND Fig 1 Connection diagram CME 331 Laboratory 5 T STOP After all errors are fixed reload the code into the LaunchPad Press both switches to simulate customer entry and exit actions Show your design to the instructor STOP In your lab notebook write down in which part of the lab you used ICDI tools to debug your design Also say how the ICDI tools helped you resolve the issue STOP In your lab notebook write substantiated conclusions for each portion of the lab Your conclusion should state what you have learnt in the lab whether or not the objectives of the learning outcomes are met and any improvements can be made in your display system References 1 CME331 class website https www engr usask ca classes CME 33 1 2 LM4F120H5QR Datasheet Aug 29 2012 http www ti com lit gpn Im4fl 20h5qr 3 Stellaris LM4F120 LaunchPad User Manual SPMU289A Revised December 2012 http www ti com tool sw ek lm4f1 20x 1 8 18 bit color TFT LCD display with microSD ST7735R http www adafruit com products 358 Adafruit GFX Graphics Library http learn adafruit com adatruit gfx graphics library Appendix A Sensor ci
4. e controlled by a set of seven registers These registers are used to select the source of the interrupt its polarity and edge properties When one or more GPIO pins cause an interrupt a single interrupt output is sent to the interrupt controller for the entire GPIO port For edge triggered interrupts software must clear the interrupt to enable any further interrupts For a level sensitive interrupt the external source must hold the level constant for the interrupt to be recognized by the controller Carefully review section 10 2 2 on p 608 for the complete interrupt handling procedure The following three registers are used to define the edge or sense that causes an interrupt GPIO PORTF IS define interrupt sensing type 0 edge 1 level p 617 GPIO PORTF IBE define single edge or both edges p 618 GPIO PORTF IEV define interrupt event 0 falling 1 rising p 619 Enabling interrupts and checking the status are done using the following four registers GPIO PORTF IM interrupt mask to individually enable disable interrupt p 620 GPIO PORTF RIS raw interrupt status p 621 GPIO PORTF MIS masked interrupt status p 622 GPIO PORTF ICR acknowledge clear interrupt flag by writing 1 p 623 CME 331 Laboratory 3 Lab procedure l The lab requires LCD display driver Like the previous two labs you may use the project template of Lab 4 Test_4a_testingLCD_webposting zip from the course website In t
5. ed and flash continuously Assume that there two doors in the store one for entry one for exit We will use two onboard switches SW1 and SW2 to simulate the entry and exit actions by customers For example pressing SW1 once means that a customer has just entered into the store while pressing SW2 indicates that a customer has just left the store These switches are active low You will use GPIO interrupt and handle more than one interrupt requests Interrupt control in Cortex M Interrupts in the LM4F120H5QR MCU are controlled by the Nested Vectored Interrupt Controller NVIC p 47 of 2 The NVIC and Cortex M4F prioritize and handle all exceptions in Handler Mode The processor state is automatically stored to the stack on an exception and automatically restored from the stack at the end of the Interrupt Service Routine ISR The interrupt vector is fetched in parallel to the state saving also known as context saving enabling CME 331 Laboratory 2 efficient interrupt entry Software can set eight priority levels 0 to 7 a higher level corresponds to a lower priority 1 e level O is the highest interrupt priority on seven exceptions such as reset software interrupt hardware interrupt bus fault etc more on p 97 and 65 interrupts More information on NVIC can be found on p 119 of 2 The vector addresses of all exceptions can be found on p 98 101 Table 2 8 and 2 9 in 2 These definitions are added in the Startup s file
6. hat case the settings needed to use the TFT LCD display are already done for you The main C code file is testingLCD c You will now focus on your design You need the definitions for Port F GPIO registers NVIC registers and SYSCTL RCGC2 followed by initialization of these registers Make sure to enable pull up resistors on PFO and PF4 and unlock PFO to use SW2 STOR demo code for GPIO interrupt using SWI on PF4 was provided on the course website You may review the code to verify the configuration for Port F interrupt Write the register values in your notebook with datasheet reference Since you will be using external interrupts generated by Port F GPIOPortF _Handler is your interrupt service routine ISR So make sure to add GPIOPortF _Handler function in your main code Handling multiple interrupts In this lab you will handle multiple interrupts Once Port F interrupt is activated pressing any switch will trigger an interrupt and the system will execute the ISR As a result you will have to determine the source of interrupt 1 e whether it is SW1 or SW2 inside the ISR This can be easily done by checking the 0 and 4 bits of GPIO PORTF MIS register Check these two bits separately and perform necessary actions For example GPIO PORTF MIS 0x10 means that the interrupt is triggered by PF4 which indicates that a customer has just entered in the store so the current customer count on the display should be i
7. ncremented Similarly GPIO PORTF MIS 0x01 tells that PFO triggered the interrupt and the count should be decremented Make sure to clear the interrupt flags before exiting the ISR In this lab you may not need to use GPIO PORTF RIS at all Before you start writing the C code it is important to have a big picture of your software There is no better way to do this than a flowchart Software flowchart is a type of diagram that shows the tasks performed in a program as boxes The order of these tasks 1s shown by connecting the boxes with arrows STOP Generate two software flowcharts one for the main function and one for the ISR Show the flowcharts to your instructor Write C code to accomplish the above mentioned tasks You may modify testingLCD c if you are using the template After the C program is written compile it and look for errors and warnings You should use the Stellaris CDI to debug your code Ask for assistance if you need help locating the debugging tools Step though the code and look for errors Take necessary steps to resolve the issue if any CME 331 Laboratory The experiment setup is shown in Fig 2 Note that during the warning event 1 e when the number of customer is over the maximum capacity the display should change the text color to red and flash continuously LITE MISO SCK MOSI TFT_CS CARD_CS D C RESET VCC GND TFT LCD Display ST7735R Capacity Fig 2 Experimental setup left norm
8. provided on the course website 1 You must download this file and use in your project Alternatively you can use the project template provided in Lab 4 or the demo code for GPIO interrupt that already has the required Startup s file Do not make any changes to the Startup s file To activate an interrupt source we need to perform two tasks a enable the source from the corresponding NVIC enable register and b set its priority using a priority register The register maps are given on p 99 and p 129 see Table 3 8 in 2 To better understand the activation procedure an example is given below Say you want to use Port F interrupt First of all find the interrupt number i e bit position in interrupt register from Table 2 9 2nd column on p 99 corresponding to GPIO Port F It 1s 30 Now find the interrupt register that is needed to enable IRQ30 from Table 3 8 p 129 It is NVIC ENO So it means that you need to set bit 30 of NVIC_ENO register to enable interrupt on Port F From Table 3 8 you will also need to find the register needed to set the priority of IRQ30 It is NVIC_PRI7 You may choose any priority value from 0 to 7 For both NVIC ENO and NVIC_PRI7 registers go to respective pages in 2 to find more instructions on how to use them You may also review the lecture notes on interrupt handling posted on the course website for details 1 Interrupt Control for GPIO The interrupt capabilities of each GPIO port ar
9. rcuit The lab uses two switches to simulate the store doors A sensor circuit could be used to simulate the actual situation The circuit diagram is given below for your future reference SEP8736 001 330 LTR 301 SEP8736 001 330 LTR 301 Fig Sensor circuit for customer counter CME 331 Laboratory 6 Appendix B LaunchPad interface The pin out diagram of the LaunchPad is given below Although the LM4F120HS5QR MCU has 43 GPIO only 35 of them are available through the LaunchPad They are 6 pins of Port A PA2 PA7 8 pins of Port B PBO PB7 4 pins of Port C PC4 PC7 6 pins of Port D PDO PD3 PD6 PD7 6 pins of Port E PEO PE5 and 5 pins of Port F PFO PF4 In addition there are two ground one 3 3V one 5V VBUS and one reset pins available on the LaunchPad Pins PCO PC3 are left off as they are used for JTAG debugging Pins PAO PAI are also left off as they are used to create a virtual COM port to connect the LaunchPad to PC These pins should not be used for regular I O purpose Besides in the LaunchPad PDO and PD1 are connected with PB6 and PB7 respectively with a OQ resistor 1 e short circuit p 20 in 3 So user needs to pay special attention when using Ports B and D at the same time J1 J3 J4 J2 3 3V VBUS PF2 GND PB GND PF3 PB2 PBO PDO PB3 PEO PB1 Ppi PC4 PFO PE4 PpD2 PC5 RST PE5 PD3 Pce PB7 PB4 PE PC7 PB6 PA
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