Rainbow Electronics Atmega169L - Manual (Page 98)

98
ATmega169V/L
2514A–AVR–08/02
Therefore, when both the main code and the interrupt code update the temporary regis-
ter, the main code must disable 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: 1. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”,
and “SBI” instructions must be replaced with instructions that allow access to
extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
The assembly code example returns the TCNT1 value in the r17:r16 register pair.
Assembly Code Example (1)
TIM16_ReadTCNT 1:
; Save global interrupt flag
in r18,SREG
; Disable interrupts
cli
; Read TCNT 1 into r17:r16
in r16,TCNT 1L
in r17,TCNT 1H
; Restore global interrupt flag
out SREG,r18
ret
C Code Example (1)
unsigned int TIM16_ReadTCNT 1( void )
{
unsigned char sreg;
unsigned int i;
/* Save global interrupt flag */
sreg = SREG;
/* Disable interrupts */
_CLI();
/* Read TCNT 1 into i */
i = TCNT 1;
/* Restore global interrupt flag */
SREG = sreg;
return i;
}