elwell@cwruecmp.UUCP (Clayton Elwell) (03/30/84)
In the process of disassembling and commenting PC-DOS 2.00 (no flames, please; I know it's masochistic but I am insatiably curious), I have discovered the purpose of reserved interrupt number 29H. It is used by the console driver to output a character. This means that if you want a new console output driver, all you need to do is intercept INT 29H and DOS will handle mutli-byte transfers, device strategy and interrupts, etc. The character to output is passed in the AL register. The default handler does not seem to preserve the registers, but it might be a good idea to do it just in case. keyboard handling remains the same. This should allow much smaller screen drivers, since DOS takes care of all of the overhead. Note: Since this is undocumented, it may well go away in future versions (though it's still there in DOS 2.10). I don't know if this "feature" is in generic MS-DOS 2.x. Happy HAcking, Clayton Elwell elwell@cwruecmp.UUCP ...!decvax!cwruecmp!elwell elwell%case@rand-relay elwell@case.csnet Clayton Elwell ...{usenet}!decvax!cwruecmp!elwell ARPA: Elwell%Case@Rand-Relay CSnet: Elwell@Case