analog_programmer wrote on 2025-09-13, 07:36:

I'm sorry for the resurrection of this thread, but I don't see any point to make a new one with the same or very similar topic.

This may be useful, if software in OpROM starts only when no-bootable drive is found. Like Predator99 made an OpROM for ROM Basic: IBM ROM Basic - option ROM for PC clones Is this impossible to be done for software in OpROM?

That's actually how ROM BASIC is meant to work. It isn't meant to run when the ROM is initialized, it's only meant to hook INT18 which the BIOS will jump to if it can't find a bootable disk.

jmarsh wrote on 2025-09-14, 21:02:

That's actually how ROM BASIC is meant to work. It isn't meant to run when the ROM is initialized, it's only meant to hook INT18 which the BIOS will jump to if it can't find a bootable disk.

Yep, and that's why I converted some ROM BASIC OpROMs form 64 kB to 32 kB size the "right way": Re: IBM ROM Basic - option ROM for PC clones

32 kB OpROMs with "Digger" and "J-Bird" games with no-boot drive boot loader are also ready, but I'll attach them tomorrow. Unfortunately "Buck Rogers: Planet of Zoom" game compressed with lz4 + lz4 decompressor stub + no-boot drive boot loader stub didn't fit in 32 kB OpROM for a few tenths of bytes.

Tronix wrote on 2019-06-04, 07:02:

And now 32Kb version! 😊

For compression i use great LZ4 program lz4_8088 by Trixter. So, original JBIRD.OVL compressed to 25795 bytes. Then insert in STUB.ASM LZ4 faster decompress and here we are! 27С256 EPROM can be used instead of 27C512.

This is the very same compressed OpROM inserted into predator99's no-boot drive boot loader, so it will start only when no bootable drive is found:

Tronix wrote on 2019-06-04, 08:20:

BTW, almost all early XT/PC games can be ported to EPROM. For example, this is digger 32Kb in attachment. Original .COM file compressed with LZ4_8088, added STUB for uncompressing and move to RAM memory at 1000h:0100h. Offset is 0100h, because digger want PSP data area.
I think its possible to convert Paratrooper, Arcade , and so on....

UPD: And "Planet Zoom"

"Arcade Volleyboll" can't be "ported to EPROM" this way. The game consists of two .EXE and .DAT files. "Paratrooper" can be ported, but I'll not publish it here as I don't know how it will be accepted.

And here is the very same compressed OpROM of "Digger" inserted into predator99's no-boot drive boot loader, so it will start only when no bootable drive is found:

And this "Planet of Zoom" inserted into predator99's no-boot drive boot loader didn't fit into 32 kB file, so I made a 64 kB OpROM: