/ xc-fetch /

Cross-Compiler's access to memory

question:: does CData contain code and data or only constant data?
answer:: (Elizabeth Rather) CData is intended as code space. (Stephen Pelc) CDATA spaces refer to code areas, basically read/execute. IDATA refers to read/write space that is automagically initialised. UDATA refers to read/write space that is NOT initialised at cross compile time. The intention on Harvard targets (e.g. AVR and 8051) is that CDATA describes the type of the CODE area, and UDATA and IDATA refer to the RAM space. If you need a third address space you'll have to invent an xDATA name for yourself. In a machine with a single adress space all three types live in the same address space. (mlg) So the best interpretation for CData is: "code and constant data".
question:: What memory access words assess what address spaces?
answer:: > "cross @" means "the version of @ used by host to write to its > image of the target memory" > > "target @" means "the version of @ used by the target system" (Stephen Pelc) I have added P for perhaps, H for Harvard and S for single address space machines. In the MPE cross compilers, @C and !C exist in the compiler in all architectures, but are mapped onto @ and ! for single address space machines. The use of @ and ! to refer to code space (even if CDATA is selected) is IMHO at the very least an ambiguous condition for a Harvard target. Exists? CData IData UData cross @ y S y P cross ! y S y P cross @C H/P H n n cross !C H/P H n n target @ y S y y target ! y S y y target @C y y n n target !C H/P P n n Note that some Harvard CPUs, e.g. Z8, do allow you to write to code space and hence !C and friends are useful in both host and target. (Elizabeth Rather) I agree with Stephen's interpretations (mlg's note: H means "yes for Harvard", S means "yes for single address space machines", H/P means "yes for Harvard, perhaps for single address space machines".)
question:: On a Harvard processor, code and data memory may use the same range of addresses (e.g. $0000..$FFFF), but belong to different spaces. Does the cross-compiler need to map these two different spaces (code and data) onto a single development space?
answer:: No. A SECTION describes the memory map of the TARGET, not where you put it during development on the HOST. The table above permits you full access to both Harvard spaces, since you must use @C and !C and friends to access data in CDATA space. The point about SECTION is that it allows you to describe several areas of each type of memory. [...] [To avoid confusion, remember that] the comma words ARE affected by the xDATA switching but that @ and ! are NOT. This is necessary so that you can build tables using CREATE, e.g. CDATA CREATE MyTable \ -- codeaddr 5 c, 7 c, ... IDATA CREATE ATable \ -- dataaddr 7 c, 9 c, ... (Elizabeth Rather) I agree with Stephen's interpretations