Interrupts Microprocessor and Interfacing 261313 Example Writing a

Interrupts Microprocessor and Interfacing 261313

Example: Writing a Game Need to Check Keyboard Input

Method 1: Using a Loop Program keeps checking for keyboard input While (1) [ If Key = Right Then move. Right Else. If Key = Left Then move. Left End If ]

Mothod II: Use Key. Press Event Runs only when there is a keyboard interrupt Key. Press. Event(Key) If Key = Left Then Move. Left Else. If Key = Right Then Move. Right End If End Subroutine

WHAT’S THE DIFFERENCE BETWEEN METHOD I - METHOD II ?

Method I : Software Polling Method II : Event or Interrupt Driven

I/O Handling Techniques n Software Polling n Interrupts n Direct Memory Access (DMA)

Benefits of Using Interrupts n Consumes much less CPU q Especially when interrupt generated by hardware n Cleaner & Simpler Code n Allows Basic Parallel Processing

Exercise: Program a PIC Microcontroller n n Blink an LED every 0. 5 sec Also receives serial data from the computer Available Commands q q Getchar() – wait and return serial data Output_toggle(LED) Time() – returns current time (in ms) Kbhit() – returns true if serial data is available

Solution Software Polling Int current. Time; Char data; start. Time = time(); While (1) { if (time() – start. Time > 500) { output_toggle(LED); start. Time = time(); } if (kbhit()) { data = getchar(); } }

Same Program with Timer Interrupt timer. ISR() { output_toggle(LED); } Main() { setup. Timer(); while (1) { data = getchar(); } }

Interrupt Handling

Multi-Interrupt Handling

Interrupt on the PIC 16

Available Interrupts n n n n INT Pin Interrupt (external interrupt) TMR 0 Overflow Interrupt PORTB Change Interrupt (pins RB 7: RB 4) Comparator Change Interrupt Parallel Slave Port Interrupt USART Interrupts Receive Interrupt Transmit Interrupt A/D Conversion Complete Interrupt LCD Interrupt. Data EEPROM Write Complete Interrupt Timer 1 Overflow Interrupt Timer 2 Overflow Interrupt CCP Interrupt SSP Interrupt

Interrupts on the PIC

Interrupts on the PIC

#INT_RBvoid rb_isr(void) { /// interrupt code } Void main() { enable_interrupts(INT_RB); enable_interrupts(GLOBAL); /// main code }

Calling the correct ISR Boot Vector INT ISR Check which INT occurred Int Timer Int Serial Int I/O etc

Context Switching: How do switch to and from an interrupt PC Saved Automatically Other registers may need to be saved, but must be done in software.

Benefits of Programming in C Everything is done for you automatically!

DMA (Direct Memory Access) CPU RAM DMA I/O (e. g. Disk) Can send data directly to and from memory

Watching a Movie: How Does the Data Flow? Display CPU RAM

Summary

Analogy I: Hanging a Picture Frame

Analogy II: A Simple Game n n n We need one volunteer The instructor will show a number to the class but hide it from the player We will simulate Polling, Interrupt, and DMA by playing this game.

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