This is the mail archive of the gcc-help@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: New datatype addition to gcc


Hi Michael,

Michael Meissner wrote:

Note, GCC internally believes that all pointers are equal and are an integer
type.


That is known.

If your port has two different types of address (ie, a pointer to 8 bit
items would be different from a pointer to 16 bit items, either using a
different format or a different sized item), it will be a long and difficult
port.

My h/w personnel says that there will be TWO RAMs in the processor, one is 8-bit addressible while the other is 16-bit addressible. If the compiler has to do 8-bit data load/store, it uses the 8-bit RAM and if it has something to do with 16-bit, it uses that RAM. This sounded bizzare to me but, thats what they say (or atleast I've never come across such stuff).

I did the front end of the C compiler for Data General MV/Eclipse
computers, which was originally a word machine that had byte modes grafted on
(byte pointer was the word pointer shift left one bit). At one point as we
were doing the transition from MV/Eclipse to Motorola 8800, I looked at GCC,
and concluded that it would be very difficult to support two types of pointer
in the compiler.


Completely agreed (though I have no clue how you do that)

If your question is instead that you have a unifed pointer mode (word pointers
having bottom bits zero), and you have load byte/store byte on the new machine,
but no byte arithmetic, don't worry, most RISC machines have that restriction.
GCC will just promote items to a larger integer type that does have arithmetic
support.


There we are. I was thinking exactly that. But again the problem of two RAM spaces is cropping up. Im totally stumped out here. I simply did not understand how the addresses are generated etc. (for eg. the arithmetic result of two 16-bit data can be 8-bit, then will it be stored in 8-bit RAM (thats what our ppl say))? And many such questions.

Im not sure if this is as unique a problem as I see or I'm still a novice in the processor world. Meanwhile our HW guys are busy with their works and have very less time for meetings on this issue.


Thanks again, Sriharsha.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]