ATMEGA8_08 Datasheet, PDF (80/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

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.
Assembly Code Example⁽¹⁾
TIM16_ReadTCNT1:
; 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
C Code Example⁽¹⁾
unsigned int TIM16_ReadTCNT1( void )
{
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;
}
Note: 1. See “About Code Examples” on page 8.
The assembly code example returns the TCNT1 value in the r17:r16 Register pair.
80 ATmega8(L)
2486T–AVR–05/08