🚀 go-pugleaf

jdl47513@uxa.cso.uiuc.edu (Jason Lowe) writes:

>I believe this may actually be possible.  I was programming SVGA assembly
>code a while back, and I do remember reading something about the Tseng Labs
>ET4000 chip set (SpeedStar I believe uses these) can map its address space
>into higher memory.  I am pretty sure the ET4000 is the only Tseng chip that
>claims to do this.  Ahh, here I found the text I read this from:

>Excerpt from _Programmer's Guide to the EGA and VGA Cards, Second Edition_
>by Richard F. Ferraro:

>(page 932)
>The [Tseng Lab ET4000] can be configured to access memory in a linear or in a
>segmented fashion through the SLS field.  This linear addressing mode forces
>all display memory to be continuous. ....  If the SLS Field is 1, this linear
>mapping scheme is enabled.  If 0, the standard VGA segmented memory mapping
>scheme is enabled.  ....it is possible to place the VGA into high memory where
>there is room to place one Megabyte of display memory into a contiguous
>address space.  This allows the ET4000 to ignore the bank selection registers.

>[text goes into more detail..]

The chip may be capable of linear addressing, but it's still up to the card
manufacturer to support this feature.  With an ISA card, I don't think it's
possible due to the fact that the ISA bus does not support 32-bit addressing.
If there is a video system that does this, chances are it is either for the
MCA, EISA, or is a motherboard implementation.

I believe Ferraro mentions the advantage of using an ET4000 on the motherboard.
It would simply use the motherboard's 32-bit memory bus and I suspect it would
really cook!


"More than 64K!  Who could possibly want more than 64K!?!"
- an IBM engineer.

					Dave Erazmus
					Champaign, IL