Radeon 9100 with 128 Mb VRAM

[snakecoils]

Hello,
I recently purchased and succesfully flashed an Hercules Prophet 8500LE (64Mb VRAM) with the standard Radeon 8500 Mac ROM, luckily the eprom was 128kb in size so no reducing was necessary.
Now I am about to purchase a Radeon 9100 128mb that I know is a 8500L£ rebadged but I fear the 8500 Mac ROM will lead to see only 64 Mb out of the 128 Mb the card could address so I suspect a ROM editing could be needed.
In the meantime I have searched the web for two 8500 ROMs (either Mac or PC) identical in revision but different for memory size to see what bits are changed between the two Bios but so far no luck.
Can someone tell me if this modification is an easy fix (i mean a couple of code locations to edit) or a deeper edit is involved? Are there some chances the memory size will be automacitally detected by the standard BIOS?
Many thanks in advance...

[snakecoils]

Well, after some troubles I have succesfully flashed the Radeon 9100 128 Mb I was talking in my previous post.
The eeprom was 128k in size so I have experimented first with the official 8500 ROM and then with the unofficial 9100 ROM from the MacElite archive.
The board itself has the classic look and feel of the ATI cards, the red PCB is the same used in many of VIVO version, without the yellow plug on the back. The memory chips are 8 (4 front + 4 back) Samsung brand, while all usual video ports are present (VGA + DVI + Svideo), "Powered by ATI" fan on the GPU heatsink.

Intial test with 8500 Mac ROM v227 was unsuccesful, the board reports 16Mb of VRAM and the image was flickering garbage, nothing was recognizable (I have the info of System profiler beacuse of a second PCI board I used as mirror display of the flashed AGP)

Second test with 9100 hacked ROM v126 (also from MacElite archive) was succesful: detected from Mac as Radeon 8500, all ports functional, VRAM size of 128 Mb and when plugged to my HDTV setup I can happily choose 1920x1080p at 24/50/60 Hz in million of colours, apparently perfect but..

While for most desktop operations all seems fine, more intensive tests show that video memory is seen but not allocated as it should.

First evidence of this was running the Amiga emulator FS-UAE: at 1280x720 the image was fine but at 1920x1080 no graphics, only sound.

Second evidence: Maxon Cinebench R10 does nothing when perfomed the OpenGL test, the main window remains grey with spinning rainbow ball.

The Hercules Prophet 8500LE (flashed with v227 official ROM) in the same situations performed perfectly, absolutely no issue at all. The only drawback is a transparent "checkerboard" I can see on darker backgrounds but this is almost for sure because of older DVI interface chip when stressed at 1920x1080 while at lower resolutions is OK.

The Hercules (64 Mb of VRAM) has 8 memory chips of Hynix brand, both boards (ATI and Hercules) are clocked to 250/250 MHz (core + memory) as a 8500LE should be.

I think a slighlty hacked 8500 v227 ROM could perform well with my board but without informations where in the ROM code is stored the memory size I can no longer do further experiments...

[snakecoils]

Just for curiosity I have purchased another Hercules 8500LE, this time the 128Mb version with 8 Samsung chips (it is the same PCB as the 64Mb version I already have, only with different chips) and the story is identical to the 9100 in my previous post: the official ATI Mac ROMs produced garbage on screen and shown only 16Mb of VRAM (System Profiler on secondary PCI video board) while the 9100 hacked ROM works well until the full video memory is requested. As for the original 9100 board I have flashed back this Hercules board to its original PC ROM, but it is really a pity that the only 128Mb "serious" board supported in OS9 is the nVidia 4600Ti, the ATI would be a great alternative (better support both in OSX and OS9), so far the only version that works as expected is the 64Mb version.
I looked in the code of different ATI ROMS but honestly I don't understand much about what to search and replace. Any of the good old firmware hackers are around to help?

[reddrag0n]

it's been awhile since i dabbled in the ppc rom area, i myself am not sure what to tell you