DOS ain't dead

Conflict between JEMMEX and BIOS service E820h (Developers)

posted by Laaca , Czech republic, 07.01.2021, 22:18

Well, things are much more compicated than I expected. I made more tests and sometimes the memory size is reported correctly and sometimes wrong.
For tests I used the Japheth's utility GETI15EX (originaly from HXDOS\TEST\ subdirectory). Not sure whether it it the last version however the file has 2374 bytes.
Also I used my quick-and-dirty utility TestMem

First of all - I have found a bug in Japheth's utility GETI15EX. It does not correctly process the E820h chain and omits the last record.
(log here )

So for further testing I used only TestMem.

And the result is that it seems to be a conflict between JEMMEX and the memory map created by BIOS service E820h.

Under these configurations is returned the proper size of my RAM (16GB):
raw DOS, HimemX, HimemX+Jemm386 (both from config.sys and commandline)
Logfile is here

But if I load JemmEX (from config.sys) the memory map is corrupted and the last entry from E820h is corrupted and is marked as memory region type 2 (aka reserved).
(See here)

I thought that JemmEX overwrites some data in some BIOS segment where the E820h map is loaded from. I suspected the page frame for EMS.
But this curruption occurs with every parametrs I tried even with such configuration when everything is off: DEVICE=C:\FREEDOS\JEMMEX.EXE MAX=32M NOVME NOEMS NOVCPI
And what is even more strange is the fact that the combination HIMEMX+JEMMEX is OK but JEMMEX not.
Any ideas?

---
DOS-u-akbar!

Complete thread:

• Wrong memory map using E820h? - Laaca, 06.01.2021, 23:30 (Developers)
  • Wrong memory map using E820h? - Laaca, 07.01.2021, 10:43
    • Conflict between JEMMEX and BIOS service E820h - Laaca, 07.01.2021, 22:18
      • Conflict between JEMMEX and BIOS service E820h - Japheth, 08.01.2021, 04:57
        • Conflict between JEMMEX and BIOS service E820h - Laaca, 08.01.2021, 13:37