Hail to the 3DFX fans! As I promissed before here are some results of my study on VSA100 cards. Some of you might know that I was a member of the team that succeded in modding a regular Voodoo4 AGP from 32MB to 64Mb RAM by hot-air soldering extra memory chips and a VGA-BIOS mod. The card worked with no problems and now is not the only one of it's kind; other mods have been performed with succes that same way. But there is a catch: allthough it was the proof that a VSA100 GPU can access up to 64MB, it was not a big step to the road of modding a Voodoo5 to more RAM, because the Voodoo4 AGP had empty spots for mounting the extra 32MB; it had all the PCB traces and all the other pieces needed for 64MB opperation. I guess it is OK to suspect that 3DFX produced this PCB design in order to be able to offer 64MB Voodoo4's if there would have been market demands at the time.
However, for the other VSA100 based cards, no succesfull moddings have been confirmed; it may be because of the fact that compatible 16MB TSOP2 RAM chips for transplant are not easy to get. I for one and I bet many of you, would love to see a working Voodoo5 with 128Mb...
For a month and a half I had no computer (MB died) and a question arised in my mind: we want for the VSA100 GPU to handle more memory; but how does it works? I have done some tests of myown; the old-"reverse engeneering"-stile and I will show what I found out. For many of you it might be old-old news, so I'm sorry if so...
First, VSA100 does not realy care about the "physical" memory chips; it does not request the TSOP2 form factor; It does not care about the number of memory chips, nor is it aware about the pinout of the RAM. All that because VSA100 access the amount of memory... let us say in a "virtual" mode. For the RAM controller of the GPU, there can be only one or two virtual memory chips. For a Voodoo4 4500 PCI is one; for the Voodoo4 4800 AGP (64MB) there are two of them. I will say how and why further. The physical RAM chips depend on the PCB design only.
From every VSA100 starts 128 traces for multiplexed in/out data; that is because all VSA100 do 128bit access to the SDRAM (32 traces for every RAM chip for a total of 4 memory chips per VSA100). On the Voodoo4 AGP design, every trace is divided in two; there are 256 in/out 1bit traces, but they are connected in couples for the above reason (32 traces per RAM chip for a total of 8.). It could not have accessed 256bit memory resulting from the number of the 8 chips by 32bits each, so here enters the second virtual memory chip: by a trace called "Chip Select", it can be assigned a second virtual bank from all the extra 4 RAM modules. For every extra memory chip on a Voodoo4 4800 PCB, all the PCB traces of a single one are the the same as for one of the orriginal ones (the 4 modules that make the factory default 32MB for V4 AGP), with the exception of the CS (chip select) trace that is the same for every group of four chips. The situation is somehow simmilar to the DIMM SDRAM modules with memory banks on both sides; they do not have double the bits band of the single sided "brothers", but they share the inputs/outputs and make the selection about where to read or write from in simple terms.
On the PCB, also shared through all the RAM chips are the rows and columns adresses. At each adress allocation can be stored the total sum of all the spaces for all the modules at that designated adress. So for the VSA100, at row1-column1 of the virtual chip we have the total of row1-column1 of memory modules 1+2+3+4 in our case; but it can be in a different number of memory modules for a different PCB design with the same result. Allthough for the second virtual chip all the adress traces are shared, the content of each allocation is differentiated by the chip-select. Other PCB traces are common for all the modules, like power or groud.
There is no question; VSA100 can access 64MB RAM! I had succes myself with modding a Voodoo4 AGP. But... Remember all those old socket7 mainboards that introduced SDRAM support? They could have used 32MB DIMMs if single sided and 64MB DIMMs only if double sided. If you put a single-sided 64Mb DIMM in one slot, it cannot see all the memory. That is because of the limitations of the RAM controller. In our case, we know that VSA100 can "see" 32Mb single-sided memory and double-sided 64Mb memory too, but is it able to "see" 64Mb single-sided? And if so, it might even use 128Mb double-sided memory for a Voodoo4 AGP PCB if the right 16Mb chips were to be found...
If the only way to access 64Mb RAM for each VSA100 is to use the double-sided style (for only a true 32Mb access per virtual chip) then I am affraid that we cannot do more, because the Voodoo4 AGP is the only PCB that has a second chip-select trace to the coresponding GPU pin (ball). We must hope that when someone will find compatible RAM chips, he will be able to point to a succes of a true 64MB per virtual memory chip...
However, this might not be the only way to do that. There seems to be another way to have it done if we look at the way the memory acces for the VSA100 works: composing 8x8Mb 16bit chips by "air-wires" (the memory modules could not be soldered directly onto the PCB, but every pin must be connected through a individual external conductor). Please look at datasheets and confirm or not that! I would try it myself but I have no VSA100 card to sacrifice, nor the money needed to buy something like a GeForce 2 128bit 64Mb SDRAM with 8 8MB 16bit TSOP2 54pin chips... I would say that it can be done; I see now nothig in theory that could not allow the success.
Long story... short... I wish good luck to you all!

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Yeah... the easyest technical work, but where to find the 16Mb chips? Until now, I do not know about any succes in this search. If I for one would have had access to a suply of such rare RAM modules, I would have give it a try a long time ago, and many others would have done the same. the are some routers and HDD and possible a verssion of Quadro video cards that have those memory chips mounted onto theyr PCB and we might be able to do the transplant, but I have no knoledge of a community member that allready might have obtained them yet... There might be a small chance for the future, though, but I do not see this as a mass modding solution...

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On the Voodoo4 AGP PCB where the second chip-select trace is present, it goes under the VSA100 for connection to it's ball(pin), but it does not have a "hole" under the GPU to identify, or I cannot find one, to translate it and use it for the other PCBs. As for soldering TSOP2-86 chips ontop... I do not see myself doing such work, not with my tools anyway, avoiding any shorts and so on... I'm sure that you, Hank, have the skills and tools to do it and maybe you could provide the exact spot of the chip-select on the back of the PCBs. That would be a huge leap forward.
Anyway, composing RAM chips could be also considered as an option, right?

This memory-chip shold be compatible.
http://www.samsung.com/products/semiconductor/Sync_AsyncDRAM/SDRSDRAM/Component/...
But they are "only" 6ns fast. Not so good for overclocking.
The other question: how to get them?

My English is now worse than I remembered by the look of my posts... Even I when I read now what I did write this morning, even I find this difficult to understand all. Allthough I have a clear picture in my mind, even in my native language, Romanian, it is not easy to make a clean exposure...
I also had the ideea of piggy-back soldering of simmilar 8MB 32bit TSOP2-86 chips ontop of the orriginal ones, pin-by-pin and pin-to-pin solder, except of the chip-select one; to invert the signal from the first chip-select pin from it's PCB trace and to connect it to the piggy-back-modules, but talking only on my behalf, I would exclude working with this type of RAM chips because the pins are each one too close to the neighbors (the nearest pins are in risc of shorts), plus that the pins are too thin and small; I might not be able to solder them by hand (not even using external coonectors, wires from PCB to RAM pins); and I see no point for TSOP86 to try a hot-air soldering with my heat-gun for a piggy-back style. That does not mean that it is a generality; they might even be many members on this board able to do just that, with the right skills and tools given.
The only reason for I considered composing 16bit memory modules is because TSOP5x chips have more space between the pins, and also the pins are larger; I simply find them easyer to work with (especialy by hand). To invert the signaling from the first virtual memory chip from the trace of the chip-select to get a signal for the second one, if this is possible, could also be applied for the composed 16bit modules; this would get us realy close to the first Voodoo5 5500 with 128Mb dream. It would also be necesary to modify the bios to "fool" the VSA100 that it has a connection, but it will empty fire. How to get a CS1 signal from CS0 one, I'm not sure yet.
I say again: I found no ball on the back side of the PCB under the VSA100 that we could use to take chip-select for the second memory bank. I could very well be wrong, so search for it anyone who can, please. With this ball found it would be much, much more easy!

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Thanks Radu; but I see nothing special on what I expose here; I feel it is only very old news and the 3DFX fans have been very much aware of those simple facts for a very long time... Please excuse me, friends, if I bother you with my talk; even better, just say if so. I had no computer for a long time so I had no chance to compare what I researched with my old-style methodes with all the previous public facts.
The thing is that I don't like working for other guys with pieces that belong to them, especialy on never tested before mods, because there is allways an important risc of permanent hardware failure. Last year a friend of mine also a member on this forum had a Voodoo4 AGP send to me to add more RAM to it; I did this mod before with succes, yet I killed his video-card while working with it and still now I feel bad because I failed his expectations. I like to work with my stuff for myself because if there is a failure, it is only me feeling sad.

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Thank you guys for the nice words, especialy to jandarsun8 and m14radu; it is good to know that there are 3DFX fans who would love to see this mod performed... and it will soon be done by someone because it is very much possible and not that hard in the end. And if other options might fail, there is a good chance that a second piggy-back soldered bank with inverted signaling from the orriginal chip-select could be given a try. My problem is that I don't know yet about a way to study the relation between CS0 and CS1. Only if they work like (when CS0=ON then CS1=OFF) and (when CS0=OFF then CS1=ON) it would be just a matter of a logical gate (transistor based) to do the job and we will have no stop to get 64Mb RAM for each VSA100 working. Else... if the other options fail too, it still could be done, but it will not be that easy... Unfortunately, I have no way to study how CS1 signaling behaves compared to CS0; but there is allways a man who has done so much for the 3DFX community over the years and could provide now some insider facts that will light up any questions without answers now; I am talking about Hank, who else, so we should wait for his oppinion.
Anyway, if somebody here has a 64MB SDRAM 128bit access GeForce or something video card with 8 TSOP 16bit memory chips and a Voodoo4 to sacrifice and he has some soldering skills, he should try the compossing memory method, why not... After all there is only to unsolder with hot air with the heat-gun the RAM from the 3DFX card and from the donnor, then to solder by hand with the soldering iron about 800 points with thin short conductors. I don't say it can be finished in 1 day, but in 1 week it should not be a problem. Then we could all of us know if it worked out or not.

Hi Komponent,

Well, like i sad before, i'm willing to help.
I will search for the specified memory modules ( 54 pin TSOP2 modules ), and don't worry if you will fry them... .. i will don't need them back.
And don't forget, you are the one who did the first voodoo4 Mod , so your'e the Man !
Keep up the good work.

Radu.

Uhm, page 41 section 3.4.3 Frame Buffer Pins;

MCLKA and MCLKB

Can I start smiling yet or am I misunderstanding what these two do?

Nice Work Komponent !
It's nice to see that people like you ( and you're unfortunately the only one i know ) are still tryng to do the memory modding on the VSA chip.
Therefore, my V5 5500 is on the way to you. At the end of the Week, you will have the needed "ingredients" to start the project.
May the voodoo spirit be with you !


Br.
Radu.