Interrupt. The AVR microcontroller and embedded systems. (Chapter 10)

1. Interrupt Chapter 10

The AVR microcontroller
and embedded
systems
using assembly and c
AVR Microcontroller and Embedded System Using Assembly and C
Mazidi, Naimi, and Naimi
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

2. Contents

Polling Vs. interrupt
Interrupt unit
Steps in executing an interrupt
Edge trigger Vs. Level trigger in external
interrupts
Timer interrupt
Interrupt priority
Interrupt inside an interrupt
Task switching and resource conflict
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

3. Polling Vs. Interrupt

Polling
Ties down the CPU
Interrupt
while (true)
{
if(PIND.2 == 0)
//do something;
}
Efficient CPU use
Has priority
Can be masked
main( )
{
Do your common task
}
whenever PIND.2 is 0 then
do something
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

4. Interrupt unit

AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

5. Steps in executing an interrupt

PB0
1
40
VCC
PB1
2
39
PA0 (ADC0)
(INT2) PB2
3
38
PA1 (ADC1)
(OC0/AIN0) PB3
4
37
PA2 (ADC2)
(SS) PB4
5
36
PA3 (ADC3)
(MOSI) PB5
6
35
PA4 (ADC4)
(MISO) PB6
7
34
PA5 (ADC5)
(SCK) PB7
8
33
PA6 (ADC6)
RESET
9
32
PA7 (ADC7)
VCC
10
31
AGND
GND
11
30
AVCC
XTAL2
12
29
PC7 (TOSC2)
XTAL1
13
28
PC6 (TOSC1)
(RXD) PD0
14
27
PC5 (TDI)
(TXD) PD1
15
26
PC4 (TDO)
(INT0) PD2
16
25
PC3 (TMS)
(INT1) PD3
17
24
PC2 (TCK)
(OC1B) PD4
18
23
PC1 (SDA)
(OC1A) PD5
19
22
PC0 (SCL)
(ICP) PD6
20
21
PD7 (OC2)
0002
ATmega32
PC:
0016
0015
0014
0013
0012
000D
0009
000A
000B
000C
0006
0008
000F
0004
000E
0007
0005
0000
SP
Stack
Address
0000
0002
0002
0004
0005
0006
0007
0008
0009
000A
000B
000C
000D
000F
000E
000F
0010
0012
0013
0014
0015
0016
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
Code
.INCLUDE "M32DEF.INC"
.ORG 0
;location for reset
JMP
MAIN
.ORG 0x02
;location for external INT0
JMP
EX0_ISR
MAIN: LDI R20,HIGH(RAMEND)
OUT
SPH,R20
LDI
R20,LOW(RAMEND)
OUT
SPL,R20
SBI
DDRC,3
;PC.3 = output
SBI
PORTD,2
;pull-up activated
LDI
R20,1<<INT0 ;Enable INT0
OUT
GICR,R20
SEI
;Set I (Enable Interrupts)
LDI
R30, 3
LDI
R31, 4
ADD
R30, R31
HERE:JMP HERE
EX0_ISR:IN
LDI
EOR
OUT
RETI
R21,PORTC
R22,0x08
R21,R22
PORTC,R21
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

6. Edge trigger Vs. Level trigger in external interrupts

LDI
OUT
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
R20,0x02
;falling
MCUCR,R20
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

7. Edge trigger Vs. Level trigger (Cont.)

AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

8. Using Timer0 overflow interrupt

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This program uses Timer0 to generate a square
wave on pin PORTB.5, while at the same time
data is being transferred from PORTC to
PORTD.
;Program 10-1
.INCLUDE "M32DEF.INC"
.ORG
0x0
;location for reset
JMP
MAIN
.ORG
0x16
;loc. for Timer0 over.
JMP
T0_OV_ISR
;----main program for initialization
.ORG
0x100
MAIN:
LDI
R20,HIGH(RAMEND)
OUT
SPH,R20
LDI
R20,LOW(RAMEND)
OUT
SPL,R20
SBI
DDRB,5 ;output
LDI
R20,0
OUT
DDRC, R20
LDI
R20,0xFF
OUT
DDRD, R20
18 int.
Timer
19
init.
LDI
R20,(1<<TOIE0)
OUT
TIMSK,R20
20
SEI
21
LDI
R20,-32 ;value for 4µs
22
OUT
TCNT0,R20
Timer
init.
23
LDI
R20,0x01
24
OUT
TCCR0,R20
25 HERE: IN
R20,PINC
26
OUT
PORTD,R20
27
JMP
HERE
28 ;--------ISR for Timer 0
29 T0_OV_ISR:
30
IN
R16,PORTB
31
LDI
R17,0x20
32
EOR
R16,R17
33
OUT
PORTB,R16
34
RETI
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

9. Timer0 compare match interrupt

using Timer0 and CTC mode generate a square wave on pin PORTB.5, while at the
same time data is being transferred from PORTC to PORTD.
.INCLUDE "M32DEF.INC"
.ORG
0x0
;location for reset
JMP
MAIN
.ORG
0x14
;location for Timer0 compare match
JMP
T0_CM_ISR
;-main program for initialization and keeping CPU busy
.ORG
0x100
MAIN:
LDI
R20,HIGH(RAMEND)
Time (µS)
OUT
SPH,R20
LDI
R20,LOW(RAMEND)
OUT
SPL,R20
HERE:
IN
R20,PINC
LDI
R20,39
OUT
PORTD,R20
OUT
OCR0,R20
;OCR0
=
39
Timer init.
JMP
HERE
LDI
R20,0x09
;--------ISR for Timer 0
OUT
TCCR0,R20
;Start Timer0
T0_CM_ISR:
SBI
DDRB,5
;PB5 as an output
IN
R16,PORTB
LDI
R20,(1<<OCIE0) ;Timer0 compare match
LDI
R17,0x20
Timer int.
OUT
TIMSK,R20
EOR
R16,R17
init.
SEI
;Set I
OUT
PORTB,R16
LDI
R20,0x00
RETI
OUT
DDRC,R20
;make PORTC input
LDI
R20,0xFF
© 2011   Pearson Higher Education,
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
OUT
DDRD,R20
;make PORTD output
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
Upper Saddle River, NJ 07458. • All Rights Reserved.

10. Interrupt priority

Highest
priority
Lowest
priority
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

11. Interrupt inside an interrupt

The I flag is cleared when the AVR begins
to execute an ISR. So, interrupts are
disabled.
The I flag is set when RETI is executed.
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

12. Task switching and resource conflict

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Does the following program work?
.INCLUDE "M32DEF.INC"
.ORG
0x0
;location for reset
JMP
MAIN
.ORG
0x14
;Timer0 compare match
JMP
T0_CM_ISR
;---------main program-----------------------------.ORG
0x100
MAIN:
LDI
R20,HIGH(RAMEND)
OUT
SPH,R20
LDI
R20,LOW(RAMEND)
OUT
SPL,R20 ;set up stack
SBI
DDRB,5 ;PB5 = output
LDI
R20,160
OUT
OCR0,R20
LDI
R20,0x09
OUT
TCCR0,R20
17
LDI
R20,(1<<OCIE0)
18
OUT
TIMSK,R20
19
SEI
20
LDI
R20,0xFF
21
OUT
DDRC,R20
22
OUT
DDRD,R20
23
LDI
R20, 0
24 HERE: OUT
PORTC,R20
25
INC
R20
26
JMP
HERE
27 ;--------------------------ISR for Timer0
28 T0_CM_ISR:
29
IN
R20,PIND
30
INC
R20
31
OUT
PORTD,R20
32
RETI
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

13. Solution 1: different registers

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Use different registers for different tasks.
.INCLUDE "M32DEF.INC"
.ORG
0x0
;location for reset
JMP
MAIN
.ORG
0x14
;Timer0 compare match
JMP
T0_CM_ISR
;---------main program-----------------------------.ORG
0x100
MAIN:
LDI
R20,HIGH(RAMEND)
OUT
SPH,R20
LDI
R20,LOW(RAMEND)
OUT
SPL,R20 ;set up stack
SBI
DDRB,5 ;PB5 = output
LDI
R20,160
OUT
OCR0,R20
LDI
R20,0x09
OUT
TCCR0,R20
17
LDI
R20,(1<<OCIE0)
18
OUT
TIMSK,R20
19
SEI
20
LDI
R20,0xFF
21
OUT
DDRC,R20
22
OUT
DDRD,R20
23
LDI
R20, 0
24 HERE: OUT
PORTC,R20
25
INC
R20
26
JMP
HERE
27 ;--------------------------ISR for Timer0
28 T0_CM_ISR:
29
IN
R21,PIND
30
INC
R21
31
OUT
PORTD,R21
32
RETI
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

14. Solution 2: Context saving

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Save the contents of registers on the stack before
execution of each task, and reload the registers at the
end of the task.
.INCLUDE "M32DEF.INC"
.ORG
0x0
;location for reset
JMP
MAIN
.ORG
0x14
;Timer0 compare match
JMP
T0_CM_ISR
;---------main program-----------------------------.ORG
0x100
MAIN:
LDI
R20,HIGH(RAMEND)
OUT
SPH,R20
LDI
R20,LOW(RAMEND)
OUT
SPL,R20 ;set up stack
SBI
DDRB,5 ;PB5 = output
LDI
R20,160
OUT
OCR0,R20
LDI
R20,0x09
OUT
TCCR0,R20
LDI
R20,(1<<OCIE0)
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19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
OUT
TIMSK,R20
SEI
LDI
R20,0xFF
OUT
DDRC,R20
OUT
DDRD,R20
LDI
R20, 0
HERE: OUT
PORTC,R20
INC
R20
JMP
HERE
;--------------------------ISR for Timer0
T0_CM_ISR:
PUSH
R20
;save R20
IN
R20,PIND
INC
R20
OUT
PORTD,R20
POP
R20
;restore R20
RETI
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.

15. Saving SREG

We should save SREG, when we change
flags in the ISR.
PUSH
IN
PUSH
...
POP
OUT
POP
R20
R20,SREG
R20
R20
SREG,R20
R20
AVR Microcontroller and Embedded System Using Assembly and C:  By: Mazidi, Naimi, and Naimi
Edited  by :  Dr. Irfan­ud Din , Prof., INHA University in Tashkent.
© 2011   Pearson Higher Education,
Upper Saddle River, NJ 07458. • All Rights Reserved.