• Please review our updated Terms and Rules here

MR-BIOS implementation in a 128KB BIOS image for a Packard Bell PB450 motherboard

R

retro-pc_user

Veteran Member
Joined
Oct 13, 2017
Messages
722
Location
SE Michigan, USA
I have no idea if this is possible or not, however, is there a way and is somebody willing to implement the MR-BIOS for a Packard Bell PB450 motherboard that has an OPTi 82C895 chipset, Cirrus Logic CL-GD5428 video?

Here's the dumped standard BIOS image when I archived the chip a couple of months ago: https://drive.google.com/open?id=1P0uAcU2msT9wtKus_yc_vI5QUEmjyb94 (128KB)

And for the 82C895 MR-BIOS: http://www.mediafire.com/file/49pbetqu7yyk4rl/OPTi_82C895_MR-BIOS_v202.zip <-- link from: https://www.vogons.org/viewtopic.php?f=61&t=59146#p658582 & http://www.vcfed.org/forum/showthre...-BIOS-ROM-file-repository&p=506385#post506385 (64KB)

The video BIOS is implemented in the chip itself and I cannot find any resources or know which lines to copy over from the 82C895 MR-BIOS image to the Packard Bell BIOS image.
 
I already successfully splittet a VGA BIOS from SYSTEM BIOS on an NCR 386 and used two chips in the end. But this is years ago and I dont remember the details. I'll try with IDA look at it.

Hopefully everything is "pretty standard", this would mean, lower 64k VIDEO bios, upper 64k SYSTEM BIOS. There must be some address decodinng logic to react on C000 segment for video bios and F000 segment for system BIOS.

Try opening the file in a hex editor and look for strings.

Do you have a EPROM burner and are you willing to do a few tries if I try to assemble the two images? I cant say for sure it will work. Maybe you have to revert to original.
 
Maybe I got it wrong. English is not my native language and sometimes I understand wrong.

I got this to my mind: You have a ROM chip that holds VIDEO and SYSTEM bios. You want to change the VIDEO BIOS to another one.

After a second read I am not sure anymore if I got it right. Changing the Video BIOS is possible. The system bios most likely not.
 
I do have an (E)EPROM programming tool and software that can read and write to my Packard Bell's BIOS chip with success. Good thing I dumped the BIOS onto my computer in case anyone needed it. Also, it's just only the one BIOS chip that has the video and system BIOS, and I'm willing to do a few attempts to see how it works and report back.
 
Ok, but I still need some clarification ;) Do you want to replace the system bios in that chip or the video bios? Video is possible, system most likely not.
 
The system BIOS in the chip itself. I sure as heck wish I can put the video BIOS on a separate spot, such as, my network card, but, that'll be impossible since the BIOS itself is 64KB and my network card only supports up to 32KB (E)EPROM chips.
 
Last edited:
I am not totally sure, but as Video BIOSes are usually at C000 segment, I think they dont support other load segments. Also, for the same reasons, I dont think network cards support mapping a ROM at C000.
I have soldered 2x32k flash chips to a piece of veroboard and soldered wires directly at the original socket back when I splitted up that NCR system ROM.
 
I am 80% sure another system bios will not work. But let's give it a try.
I've ran this through IDA's auto-analyze, but totally like expected, auto analyze gives me garbage in terms of what it is declaring as data, code, ...
It says ~90% of the image is data, this could be, but is verly unlikely, that a BIOS+VIDEO_BIOS only take 12k.

Next step, looked for strings. It looks like that the VIDEO BIOS is before the SYSTEM bios.

Next step, I searched for x86 reset vectors. They are not there, where I expect them. This is why I don't trust me, having em found. Dead end.

Next step, I converted the whole image you have uploaded to a picture, rendering it as 8bit wide font (x size = 8, fits for 8x8 8x14 and 8x16).
This showed up two times the same charset, so no further clue from this...01-00200.jpg

Before I go back to IDA i want you to do one more thing.
Use "ree" (I attached, "rom extension extractor") to get the two images from the place where they are mapped (usually 0xC0000 and 0xF0000).
Once I have these two extracted images I should easily be able to locate offset in your 128k-image. Once we have the storage-addresses and sizes we can easily put another BIOS into that place that fits and try on your machine.

You start ree.exe, it beeps and shows some ASCII chars and most likely finds a video bios at C0000 in the beginning. It asks wheter to extract or not - extract.
He runs more addresses to search, but does not extract SYSTEM BIOS by default.
This is done by "ree /sys". You end up with C000.ROM and F000.ROM. These two files I need.
View attachment ree.zip
 
There seems to be some kind of unpacking mechanism or at least 1 bit altered. Both images are not directly 1:1 in that big image. This would have been easy...

I am going to prepare a empty 128k image with the MR-BIOS in it, where usually system BIOSes are located, F000 segment. Do you have a VGA-disable jumper and in best case an extra ISA VGA card?

Disable the onboard card, as the test-rom has no video bios. Without video card testing also should work. If you have one, burn the ROM, plug in, disabled onboard vga. Turn on. Keyboard lights flash if working BIOS. Either boots without video and without error or beeps for missing video.

If you have a video card, the rom without video bios works you should be able to boot it and use it. But I doubt everything is that easy...
If it works, I place the C000.ROM at beginning of image.

Comes a bit later, short in time now.

32k is very common for video bioses, also for later ones. I just analysed over 100 video bios fonts from 30-40 video roms in different ages. Most of them are 32k.
My commodore 386 also has a 128k chip and uses only 96k.
 
Unfortunately, I don't have any spare ISA video cards in my collection or in my house.

Also, my network card is able to read the ROM address at C0000, but, I have no idea if I can put the video BIOS programmed to the EEPROM onto the network card itself.
 
How's it hanging? I'm planning on testing the video BIOS on the 3Com EtherLink III card to see if it works and flash the MR-BIOS to the BIOS chip as well.
 
You must log in or register to reply here.
Back
Top