Author: Robert Hyatt
Date: 14:53:56 02/05/99
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On February 05, 1999 at 02:58:09, Ed Schröder wrote: >>Posted by Robert Hyatt on February 04, 1999 at 22:20:00: > >>>Extended memory is a way to avoid the problem. I adviced Ed to write a DOS >>>program that would allocate all DOS memory for itself, and then start >>>Rebel by a system() call. > >>>This way, the DOS extender Ed uses will be forced to load Rebel.exe into >>>extended memory (above the first megabyte), thus protecting it from memory >>>overwrites by the Auto232 driver. > >>>This is not perfect, because of course any TSR program can also access >>>extended memory. But it is unlikely to happen accidentally in this case. > >>>The bad case would be that the driver overwrites the BIOS or DOS memory >>>area. In this case there is nothing to do. But at least the program's code can be >>>protected (unperfectly I know) by forcing the system to load it above the >>>first megabyte. > > >>the only problem with the 'executable' sitting above 1M is that the thing has >>to use a 'bounce buffer' to work when you do _any_ I/O at all. Which is not >>efficient at all. Because you can't pass addresses above 1M to DOS, you have >>to copy from the local buffer to something in the first 1M, then do the I/O, >>then copy the results back, and so forth. No I/O and it works well. But if >>you update the screen quite a bit, it can wreck havoc.. > >I have made such a small program Christophe suggested. Sofar I have not >seen the problems you describe. Maybe it's all taken care of by the compiler >because I know the 32-bit DOS extender of the compiler includes special code >to the executable to handle all 16-DOS interrupt calls for all IO handling. > >Ed That is usually called a 'bounce buffer'... it isn't your responsibility because you have no idea where you are in memory. The dos extender does it... but if you do a lot of I/O or system calls (checking for a key press, for example) it can hurt performance significantly...
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