ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 95

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

7701E–AVR–02/11
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 16-bit register and the interrupt code
updates the temporary register by accessing the same or any of the other 16-bit timer regis-
ters, then the result of the access outside the interrupt will be corrupted. Therefore, when both
the main code and the interrupt code update the temporary register, the main code must dis-
able the interrupts during the 16-bit access.
The following code examples show how to do an atomic read of the TCNT1 Register contents.
Reading any of the OCR1A/B or ICR1 Registers can be done by using the same principle.
Note:
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
Assembly Code Example
C Code Example
TIM16_ReadTCNT1:
unsigned int TIM16_ReadTCNT1( void )
{
}
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT1 into r17:r16
in r16,TCNT1L
in r17,TCNT1H
; Restore global interrupt flag
out SREG,r18
ret
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT1 into i */
i = TCNT1;
/* Restore global interrupt flag */
SREG = sreg;
return i;
1. See
“About Code Examples” on page
(1)
(1)
Atmel ATtiny24/44/84 [Preliminary]
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