FACULTY OF ENGINEERING LAB SHEET

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FACULTY OF ENGINEERING LAB SHEET EMBEDDED SYSTEM DESIGN ECE3196 TRIMESTER 2 (2015/2016) : Development of a simple embedded system scheduler *Note: On-the-spot evaluation may be carried out during

1 FACULTY OF ENGINEERING LAB SHEET EMBEDDED SYSTEM DESIGN ECE3196 TRIMESTER 2 (2015/2016) : Development of a simple embedded system scheduler *Note: On-the-spot evaluation may be carried out during or at the end of the experiment. Students are advised to read through this lab sheet before doing experiment. Your performance, teamwork effort, and learning attitude will count towards the marks.

2 : Development of a simple embedded system scheduler Objectives: To demonstrate the external interrupt and timer interrupt operations of an ARM Cortex M0 based microcontroller. To develop C programs for a simple embedded system scheduler using the timer interrupt Equipment: Desktop computer with USB interface USB A-to-mini B cable Nu-LB-NUC140 learning board Windows 7 and Keil Vision IDE Introduction In the experiments conducted in ESD1, we have been using this code structure: void main(void) { /* initialize task X*/ X_Init(); } While (1){ X(); /* run task X */ } The problem with this code structure is that it is very hard to execute task X at precise intervals of time; especially if we code in C language. Very often, embedded system application requires periodic execution of tasks. Examples are: The display must be refreshed the display every 40ms The keypad must be scanned every 20ms The stepper motor excitation pattern must be updated every 5ms and many more One solution would be to add a delay to simulate the periodicity of the task: void main(void) { /* initialize task X*/ X_Init(); } while(1){ X(); /* run task X */ Delay_50ms(); /* delay for 50ms */ } This is fine, if we know the precise duration of task X, and, this duration never changes. However, in real-world applications, these conditions are very hard to meet. Page 2 of 11

3 External Interrupts 1. Each GPIO pin can be set as chip interrupt source by setting correlative GPIOx_IEN bit and GPIOx_IMD. 2. There are four types of interrupt condition can be selected: low level trigger, high level trigger, falling edge trigger and rising edge trigger. 3. The following functions can be used to enable or disable the INT0 (GPB14) or INT1 (GPB15) external interrupts: DrvGPIO_EnableEINTx (TriggerType, Mode, Callback) Use DrvGPIO_EnableEINT0 for INT0 (GPB14) or DrvGPIO_EnableEINT1 for INT1 (GPB15) Description: Enable the interrupt function for external GPIO interrupt from INTx pin. TriggerType: It could be E_IO_RISING, E_IO_FALLING or E_IO_BOTH_EDGE Mode: It could be E_MODE_EDGE or E_MODE_LEVEL to control the interrupt is by edge trigger or by level trigger. Callback: It is the function pointer of the external INT0 callback function DrvGPIO_DisableEINTx () Use DrvGPIO_DisableEINT0 for INT0 (GPB14) or DrvGPIO_DisableEINT1 for INT1 (GPB15) Description: Disable the interrupt function for external GPIO interrupt from INTx pin. 4. For edge trigger condition, user can enable input signal de-bounce function to prevent unexpected interrupt happened which caused by noise. 5. To enable or disable the debouncing of a GPIO pin, the following functions can be used: DrvGPIO_EnableDebounce (Port, Pin) Description: Enable the de-bounce function of the specified GPIO input pin. Port: It could be E_GPA, E_GPB, E_GPC, Pin: Specify pin of the GPIO port. It could be 0~15. DrvGPIO_DisableDebounce (Port, Pin) Description: Disable the de-bounce function of the specified GPIO input pin. Port: It could be E_GPA, E_GPB, E_GPC, Pin: Specify pin of the GPIO port. It could be 0~15. Timer Interrupt 1. The NUC140 has a timer controller which includes four 32-bit timers, TIMER0~ TIMER3, which allows user to easily a timer control for application. 2. The timer can perform functions such as frequency measurement, event counting, interval measurement, clock generation, delay timing etc. 3. The timer can generate an interrupt signal upon timeout, or provide the current value during operation. 4. Below is a list of features of the on-chip timers: 4 sets of 32-bit timers with 24-bit up-timer and one 8-bit pre-scale counter Independent clock source for each timer Provides one-shot, periodic, toggle and continuous counting operation modes Time out period = (Period of timer clock input) * (8-bit pre-scale counter + 1) * (24-bit TCMP) Page 3 of 11

Maximum cycle time = (1 / T MHz) * (2 8 ) * (2 24 ), T is the period of timer clock 24-bit timer value is readable through TDR (Timer Data Register) Support event counting function to count the event

4 Maximum cycle time = (1 / T MHz) * (2 8 ) * (2 24 ), T is the period of timer clock 24-bit timer value is readable through TDR (Timer Data Register) Support event counting function to count the event from external pin Support input capture function to capture or reset counter value Timer Operation Modes 1. Timer controller provides one-shot, period, toggle and continuous counting operation modes. 2. It also provides the event counting function to count the event from external pin and input capture function to capture or reset timer counter value. Timer Initialization The following steps are required to initialize the timer. Start Enable and select timer clock source Select operating mode Select time out period Enable interrupt Enable timer module End Page 4 of 11

5 Experiment A: External Interrupt 1. The external interrupt 1 (INT1) is connected to a push-button (tact switch) on the Nu-LB- NUC140 learning board. 2. In this experiment, a program with events triggered by the external interrupt will be developed. 3. The schematic diagram for the switch connected to INT1 is shown in Figure A.1. Figure A.1: Schematic diagram of the push-button connected to INT1. 4. Launch Keil Vision and open the project Smpl_GPIO_EXTINT1. 5. Refer to Appendix A to build the project and run the codes on the learning board. 6. Exercise A: Analyze the codes and enhance/modify them so that the INT1 push-button will toggle (turning on or off) the buzzer which will beep at a frequency of 2Hz (on and off every 0.25s), each time the push-button is pushed and released. Page 5 of 11

6 Experiment B: Controlling LEDs with Timer Interrupt 1. In this experiment, a program to control the single color LEDs via timer interrupt will be developed. 2. The schematic diagram below depicts the connections for the single color LEDs. Figure B.1: Schematic diagram of single color LEDs. 3. Launch Keil Vision and open the project Smpl_Timer_LED. 4. Follow the instructions in Appendix A to build the project and run the codes on the learning board. 5. Exercise: Analyze the codes to understand how timer interrupt is initialized and utilized to control the LED. Make necessary changes to the codes so that LED5 will blink at a frequency of 2Hz, LED6 will blink at a frequency of 4Hz and LED7 will blink at a frequency of 8Hz. Is it possible to implement these operations by using only one timer interrupt? Page 6 of 11

7 Experiment C: Controlling Seven-segment Display with Timer Interrupt 1. The Nu-LB-NUC140 learning board is equipped with a four-digit seven-segment display. 2. This experiment will develop a program to control the seven-segment display using the timer interrupt. 3. The schematic diagram of the seven-segment display is shown in Figure C.1. Figure C.1: Schematic diagram of seven-segment display. 4. The seven-segment display can be controlled using the seven-segment driver (Seven_Segment.c) which provides the following functions: a. show_seven_segment (DIGIT, NUM) DIGIT : select 1st/2nd/3rd/4th 7-segment LED NUM : value of the digit (0~9) b. close_seven_segment () Turn off all four 7-segment LEDs 5. Launch Keil Vision and open the project Smpl_Timer_7seg. 6. Build the project and run the codes by following the instructions in Appendix A. 7. Exercise: Analyze the codes to understand how the seven-segment display is driven by the timer interrupt. Modify/enhance the codes to implement a 4-digit timer; the two leftmost digits are showing minutes, while the rightmost two digits are showing seconds. Once the Page 7 of 11

8 maximum time is reached (59:59), the timer will automatically reset back to 00:00. The operation is repeated until the system is reset or the power is removed. Experiment D: Controlling LCD with Timer Interrupt 1. The Nu-LB-NUC140 learning board comes with a 128x64 pixels graphical LCD. 2. In this experiment, a program to increase and display a timer on the LCD will be developed. 3. Figure D.1 below illustrates the schematic diagram for the graphical LCD. Figure D.1: Schematic diagram of the graphical LCD. 4. Launch Keil Vision and open the project Smpl_Timer_LCD. 5. Refer to the instructions on Appendix A to build the project and run the codes on the learning board. 6. Exercise: Analyze the codes to study different operating modes of the timers as well as how timer interrupt can be used to increase the time shown on the LCD. Enhance the codes to implement a timer on the LCD with the first line showing the minutes and the second line showing the seconds. The timer will start immediately when the system is power on. It will stop when INT1 push-button is pushed and released, and resume when INT1 push-button is pushed and released the next time. In addition, the buzzer will beep for 0.5s every 30 seconds. Page 8 of 11

9 Appendix A: Build and Run Codes on Nu-LB-NUC140 Learning Board Step 1 Step 2 Step 3 Page 9 of 11

10 Step 4 Step 5 Page 10 of 11

11 Step 6 Step 7 Page 11 of 11

EIE/ENE 334 Microprocessors

EIE/ENE 334 Microprocessors Lecture 12: NuMicro NUC140 Week #12 : Dejwoot KHAWPARISUTH Adapted from http://webstaff.kmutt.ac.th/~dejwoot.kha/ NuMicro NUC140: Technical Ref. EIE/ENE 334 ARM Cortex-M0 Page