Imagecraft c compiler and development environment for the atmel avr

PROGRAMMING THE AVRAccessing AVR FeaturesThe strength of C is that while it is a high-level language, it allows you to access lowlevelfeatures of the target devices. With this capability, there are very few reasons touse assembly except in cases where optimized code is of utmost importance. Even incases where the target features are not available in C, usually inline assembly andpreprocessor macros can be used to access these features transparently.The header files io*v.h (io8515v.h, iom103v.h, and so forth) define devicespecificAVR IO registers, and the file iccioavr.h can be used in place of theio*v.h file as it conditionally includes all the io*v.h files based on the device macropassed down by the IDE. The file AVRdef.h defines many useful macros. Forexample, the macro UART_TRANSMIT_ON() can be used to turn on the UART (whenavailable on the target device).The compiler is smart enough to generate the single-cycle instructions such as in,out, sbis, and sbi when accessing memory-mapped IO. See IO Registers.Since AVR’s native addressing space is 16 bits, most of the following sections discussaccessing less than 16 bits of data space or 16 bits of program space. To accessmemory beyond the normal range, see Accessing Memory Outside of the 64K Range.