EE 308: Microcontrollers

Transcription

1 EE 308: Microcontrollers Interrupts Aly El-Osery Electrical Engineering Department New Mexico Institute of Mining and Technology Socorro, New Mexico, USA March 1, 2018 Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

2 Polling vs interrupts Polling: The program keeps checking for a change Keeps the microcontroller away from doing other things Interrupts: The microcontroller polls a signal for changes If change occurs, the program in interrupted If no change the program runs as normal Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

3 Interrupt control Interrupt enable: If a particular interrupt is enabled, the corresponding Interrupt Service Routine (ISR) will be called if triggered Interrupt flag: When an interrupt occurs a corresponding flag is set to indicate that the interrupt happened Global interrupt enable: allows the program to enable/disable all currently enabled interrupts Both the interrupt enable bit for a particular interrupt and the global interrupt enable bit must be set for an that interrupt to occur Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

4 Interrupt trigger There are several ways the interrupt trigger may be set Level-trigger: in ATMega1284 that would be low Any logic changes Rising edge Falling edge Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

5 Interrupt vector table A table that has the address associated with a particular interrupt Address Labels Code Comments 0 x0000 jmp RESET ; Reset 0 x0002 jmp INT0 ; IRQ0 0 x0004 jmp INT1 ; IRQ1 0 x0006 jmp INT2 ; IRQ2 0 x0008 jmp PCINT0 ; PCINT0 0 x000a jmp PCINT1 ; PCINT1 0 x000c jmp PCINT2 ; PCINT2 0 x000e jmp PCINT3 ; PCINT3 0 x0010 jmp WDT ; Watchdog Timeout 0 x0012 jmp TIM2_ COMPA ; Timer2 CompareA 0 x0014 jmp TIM2_ COMPB ; Timer2 CompareB 0 x0016 jmp TIM2_ OVF ; Timer2 Overflow 0 x0018 jmp TIM1_ CAPT ; Timer1 Capture For ATmega1284, each interrupt vector occupies to instruction words Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

6 Interrupt vector table (continue) A table that has the address associated with a particular interrupt 0 x001a jmp TIM1_COMPA ; Timer1 CompareA 0 x001c jmp TIM1_COMPB ; Timer1 CompareB 0 x001e jmp TIM1_OVF ; Timer1 Overflow 0 x0020 jmp TIM0_COMPA ; Timer0 CompareA 0 x0022 jmp TIM0_COMPB ; Timer0 CompareB 0 x0024 jmp TIM0_OVF ; Timer0 Overflow 0 x0026 jmp SPI_STC ; SPI Transfer Complete 0 x0028 jmp USART_RXC ; USART RX Complete 0 x002a jmp USART_UDRE ; USART UDR Empty 0 x002c jmp USART_TXC ; USART TX Complete 0 x002e jmp ANA_COMP ; Analog Comparator 0 x0030 jmp ADC ; ADC Conversion Complete 0 x0032 jmp EE_RDY ; EEPROM Ready 0 x0034 jmp TWI ; 2 wire Serial 0 x0036 jmp SPM_RDY ; SPM Ready 0 x0038 jmp USART1_RXC ; USART1 RX Complete 0 x003a jmp USART1_UDRE ; USART1 UDR Empty 0 x003c jmp USART1_TXC ; USART1 TX Complete ; 0x003E RESET : ldi r16,high ( RAMEND ) ; Main program start 0x003F out SPH, r16 ; Set Stack Pointer to top of RAM 0x0040 ldi r16,low ( RAMEND ) 0x0041 out SPL, r16 0 x0042 sei ; Enable interrupts 0x0043 <instr > xxx Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

7 Interrupt priorities Interrupt with the lower address has higher priority In ATmega1284 any interrupt will interrupt an ISR (it might be a good idea to disable the global interrupt flag to avoid that) Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

8 Interrupt process 1 Set interrupt flag 2 Finish current instruction 3 Jumps to the interrupt vector table 4 The interrupt vector table directs the microcontroller to the interrupt service routine (ISR) 5 Microcontroller runs the ISR until the end and executes the RETI Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

9 Important points save SREG be careful manipulating the stack number of pushes and pops need to be the same figure out whether you want to allow nested interrupts or not if you don t want nested interrupts make sure you disable the global interrupt flag till you are done make sure that external input don t have noise that will trigger multiple interrupts Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

10 Using assembly. NOLIST. INCLUDE " m1280def. inc ". LIST. section. text. org 0 x00 jmp main. org INT1addr *2 jmp interruptisr1. section. text main : ; Initialize stack pointer ldi r16, lo8 ( RAMEND ) out SPL, r16 ldi r16, hi8 ( RAMEND ) out SPH, r16 ; some code ; Enable external interrupt 1 lds r16, EICRA ori r16, (1<< ISC11 ) (1<< ISC10 ) sts EICRA, r16 in r16, EIMSK ori r16, (1<< INT1 ) out EIMSK, r16 ; some code ; Enable interrupts sei here : rjmp here interruptisr1 : ; some code reti Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11

11 Using C avr interrupts.html # define F_CPU ( UL) # include <avr /io.h> # include <avr / interrupt.h> int main ( void ) { // some code // Set up interrupts EICRA = ( EICRA ((1 < < ISC10 ) (1<< ISC11 )); EIMSK = (1<< INT1 ); // some code sei (); } while (1); return 0; ISR ( INT1_vect, ISR_BLOCK ) { // some code } Aly El-Osery (NMT) EE 308: Microcontrollers March 1, / 11