Imagecraft c compiler and development environment for the atmel avr

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ICCV8 for AVR – C Compiler for Atmel AVRIf you reference any text area function by address, then it must be done indirectly. Itsaddress must be put in a word in the area func_lit. At runtime, you must dereferencethe content of this word to get the correct address of the function. Note thatif you are using C to call a function indirectly, the compiler will take care of all thesedetails for you. The information is useful if you are writing assembly code.Temporarily Deactivating the Code CompressorSometimes you may wish to disable the code compressor temporarily. For example,perhaps the code is extremely timing-sensitive and it cannot afford to lose cycles bygoing through the extra function call and return overhead. You can do this bybracketing code fragments with an instruction pair:asm(“.nocc_start”);...asm(“.nocc_end”);The code compressor ignores the instructions between these assembler directives inthe fragment.The compiler provides the following macros in the system include file:COMPRESS_DISABLE; // disable Code CompressorCOMPRESS_REENABLE; // enable Code Compressor againfor use in C programs.178
ICCV8 for AVR – C Compiler for Atmel AVRAssembler SyntaxWord vs. Byte Operands and the ‘ (backquote) OperatorThe FLASH program memory of the AVR is addressed either as words if it is viewedas program instructions or as bytes if it is used as read-only tables and such. Thus,depending on the instructions used, the operands containing program memoryaddressed may be treated as either word or byte addresses.For consistency, the ICCV8 for AVR assembler always uses byte addresses. Certaininstructions, for example, the JMP and CALL instructions, implicitly convert the byteaddresses into word addresses. Most of the time, this is transparent if you are usingsymbolic labels as the JMP/CALL operands. However, if you are using a numericaddress, then you must specify it as a byte address. For example,jmp 0x1F000jumps to the word address 0xF800. In the cases where you need to specify a wordaddress (e.g., using a .word directive), you can use the ‘ (backquote) operator:PL_func::.word ‘funcputs the word address of func into the word at location specified by PL_func.The assembler has the following syntax. Note that different vendors have their ownassemblers and it’s likely that our directives are different from other vendors.Generally, our assemblers are assumed in tandem with our compilers with the mainobligation satisfying the demand from the compilers.NamesAll names in the assembler must conform to the following specification:(‘_’ | [a-Z]) [ [a-Z] | [0-9] | ‘_’ ] *That is, a name must start with either an underscore ( _) or an alphabetic character,followed by a sequence of alphabetic characters, digits, or underscores. In thisdocument, names and symbols are synonyms for each other. A name is either thename of a symbol, which is a constant value, or the name of a label, which is the valueof the Program Counter (PC) at that moment. A name can be up to 30 characters inlength. Names are case-sensitive except for instruction mnemonics and assemblerdirectives.179
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Imagecraft c compiler and development environment for the atmel avr

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