Micro Firmware Tech Support

DEBUG Script to Disable/Enable Internal Cache on 486 CPUs

WWW URL:  http://www.firmware.com/support/bios/cacheoff.htm
FTP URL:  ftp://ftp.firmware.com/text/cacheoff.txt
Revision: 06/17/96  TLS  Micro Firmware Technical Support
Summary:  DEBUG script to create program to turn off internal CPU
          cache on 486 CPUs. Modern BIOSes normally enable the CPU
          cache automatically.

Some BIOSes will allow the internal CPU cache to be enabled or disabled. Most modern BIOSes, including Phoenix 4.xx, will automatically enable the internal CPU cache and there is not normally an option in CMOS setup to disable it as there is normally no need to do so. There may be some older DOS programs that need the cache disabled. This DEBUG script will create a program to disable the internal CPU cache and a program to enable it.

Here is a complete debug session transcript to create CACHEON.COM and CACHEOFF.COM. The dashes and colons are prompts that DEBUG uses, and aren't part of what to type in. These programs are not BIOS specific, so they should work with any system with a 486 processor. The only caveat is that certain programs may re-enable the 486 cache; the main group of programs that are likely to do this is programs that use a DOS extender.

- e 100 0f 09 0f 20 c0 66 25 ff ff ff 9f 0f 22 c0 b8 4c 00 cd 21
- r cx
CX 0000 (output from debug)
:13 (type 13 at colon prompt)
- n cacheon.com (names program)
- w (writes program to disk)
Writing 00013 bytes (output from debug)
- e 106 0d 00 00 00 60
- n cacheoff.com (names program)
- w (writes program to disk)
Writing 00013 bytes (output from debug)
- q (quits to DOS prompt)
CACHEON.COM and CACHEOFF.COM should now be present in the current directory. After turning cache off with CACHEOFF.COM, it should automatically be re-enabled when system is powered off and back on or it can be re-enabled with CACHEON.COM.


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