Imagecraft c compiler and development environment for the atmel avr

ICCV8 for AVR – C Compiler for Atmel AVRRelative Jump/Call WrappingOn devices with 8K of program memory, all memory locations can be reached with therelative jump and call instructions (rjmp and rcall). To accomplish that, relativejumps and calls are wrapped around the 8K boundary. For example, a forward jump tobyte location 0x2100 (0x2000 is 8K) is wrapped to the byte location 0x100.This option is automatically detected by the Project Manager whenever the target’sprogram memory is exactly 8192 bytes.M128x ConsiderationsThe M128x AVRs have 128K bytes of flash. Indirect function calls use 16 bit wordpointers and can reach the entire address space (see Program Areas for descriptionof func_lit) and you do not need to do anything special when using functionpointers.However, to access constant in the upper 64K bytes, you will need to modify theRAMPZ IO register to point to the upper bank manually (and reset it when done). Wemay add support for “far” pointers in the future so constant accesses will betransparent, albeit at the cost of larger code size.M256x ConsiderationsThe M256x AVRs have 256K bytes of flash. A 16-bit word pointer is no longersufficient to hold the value of all possible function addresses. For each functionpointer, a 3-byte entry is made in the efunc_lit area (see Program Areas). Theefunc_lit must be located in the lower 64 bytes of the address space.For constant data, the same issue as with M128x applies and you must set theRAMPZ IO register explicitly.XMega ConsiderationsThe XMega is large backward compatible with the ATMega devices. One notabledifference is that the CPU registers are no longer mapped onto data memory spaceand the IO registers have the same IO memory addresses and data memoryaddresses. In previous AVRs, the IO registers are offset by 32 bytes when referencedin the data memory space. Also see Accessing Memory Outside of the 64K Range forissues on accessing extended memory space using RAMPD, RAMPX, RAMPY andRAMPZ registers.140