Imagecraft c compiler and development environment for the atmel avr

ICCV8 for AVR – C Compiler for Atmel AVRIO RegistersIO registers, including the Status Register SREG, can be accessed in two ways. TheIO addresses between 0x00 to 0x3F can be used with the IN and OUT instructions toread and write the IO registers, or the data memory addresses between 0x20 to 0x5Fcan be used with the normal data accessing instructions and addressing modes. Bothmethods are available in C: Data memory addresses. A direct address can be used directly through pointerindirection and type casting. For example, SREG is at data memory address 0x5F:unsigned char c = *(volatile unsigned char *)0x5F;// read SREG*(volatile unsigned char *)0x5F |= 0x80;// turn on the Global Interrupt bitNote that for non-XMega devices, data memory 0 to 31 refer to the CPU registers!Care must be taken not to change the CPU registers inadvertently.This is the preferred method, since the compiler automatically generates the lowlevelinstructions such as in, out, sbrs, and sbrc when accessing data memory inthe IO register region. IO addresses. You may use inline assembly and preprocessor macros to accessIO addresses:register unsigned char uc;asm(“in %uc,$3F”); // read SREGasm(“out $3F,%uc”); // turn on the Global Interrupt bitThis is not recommended, as inline assembly may prevent the compiler fromperforming certain optimizations.Note: To read a general-purpose IO pin, you need to access PINx instead of PORTx,for example, PINA instead of PORTA. Please refer to Atmel’s documentation fordetails.121