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Re: [avr-libc-dev] Re: Far addresses in flash

From: E. Weddington
Subject: Re: [avr-libc-dev] Re: Far addresses in flash
Date: Thu, 02 Jun 2005 13:42:01 -0600
User-agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)

Björn Haase wrote:

Am Donnerstag, 2. Juni 2005 14:57 schrieb Per Arnold Blåsmo:
Although I think it would have been best to have the possibilities to
support 24bits pointers in avr-gcc.

Per A.

The root of the problem, IMVHO is that what one is looking for in fact is not only 24 bit pointers but various distinct classes of pointers, i.e. support for different types of memories: Pointers to Ram (probably 16 bits wide), Pointers to Flash (both 16 bits and 24 bits) Pointers to EEPROM (possibly also in two flavours with 16 bits and 24 bits , etc.). Presently, IIUC, gcc has support only for one single class of pointer: The case for conventional C.

IMO, switching PMODE to PSImode (4-Byte integer, only partially used) is not a solution since it would change the width of all pointers at the same time. E.g. also RAM pointers and EEPROM pointers would happen to be 32 bits wide what is certainly not useful.

A real solution of the issue would, IMO, require that someone adds functionality for supporting different memory spaces within gcc's C/C++ front-end and gcc's mid-end.

You're right, that's the best, and most needed solution.
However, *is* it possible to have 24-bit pointers in GCC (as opposed to 32-bit)? How difficult would that be?


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