Using Interrupts in AVR GCC

When we use interavrupqts in assembly language, we need to make sure that the interrupt vector jump table, which needs to be set up starting at address 0x00, is properly set up. The names we need to use for each possible interrupt source are defined in the datasheet for the chip being used. From that document (page 65) we see this table:

VectorNo	Address	Name	Definition
0	0x0000	RESET	Power-on Reset
1	0x0002	INT0_vect	External Interrupt Request 0
2	0x0004	INT1_vect	External Interrupt Request 1
3	0x0004	PCINT0_vect	Pin Change Interrupt Request 0
4	0x0008	PCINT1_vect	Pin Change Interrupt Request 1
5	0x000A	PCINT2_vect	Pin Change Interrupt Request 2
6	0x000C	WDT_vect	Watchdog Time-out Interrupt
7	0x000E	TIMER2_COMPA_vect	Timer/Counter2 Compare Match A
8	0x0010	TIMER2_COMPB_vect	Timer/Counter2 Compare Match A
9	0x0012	TIMER2_OVF_vect	Timer/Counter2 Overflow
10	0x0014	TIMER1_CAPT_vect	Timer/Counter1 Capture Event
11	0x0016	TIMER1_COMPA_vect	Timer/Counter1 Compare Match A
12	0x0018	TIMER1_COMPB_vect	Timer/Counter1 Compare Match B
13	0x001A	TIMER1_OVF_vect	Timer/Counter1 Overflow
14	0x001C	TIMER1_COMPA_vect	Timer/Counter0 Compare Match A
15	0x001E	TIMER1_COMPB_vect	Timer/Counter0 Compare Match A
16	0x0020	TIMER0_OVF_vect	Timer/Counter0 Overflow
17	0x0022	SPI_STC_vect	SPI Serial Transfer Complete
18	0x0024	USART_RX_vect	USART Rx Complete
19	0x0026	USART_UDRE_vect	USART Data Register Empty
20	0x0028	USART_TX_vect	USART Tx Complete
21	0x002A	ADC_vect	ADC Conversion Complete
22	0x002C	EE_READY_vect	EEPROM Ready
23	0x002E	ANALOG_COMP_vect	Analog Comparator
24	0x0030	TWI_vect	2-wire Serial Interface
25	0x0032	SPM_READY_vect	Store Program Memory Ready

If you dig into the AVR_GCC files, you will find a file named Interrupts.h where a handy ISR macro is defined. We can use this macro to set up the required entry in the vector table:

#define ISR(vector)

The actual macro is more complex than this, but this will work for our assembly language work. The vector names we need to use are define din the table above.

As an example, here is how we would set up the required entry in the vector table for using the counter compare interrupt for Timer1:

;
        org 0x0000
RESET   rjmp        start

        org 0x0016
        rjmp        Timer1_ISR

start:  ; main code goes here
        ...

Timer1_ISR:
        ; code for interrupt service routine goes here.