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barlad
l33t
Joined: 22 Feb 2003
Posts: 673
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 Posted: Tue Mar 25, 2003 7:24 pm Post subject: AGP3.0 technical question |
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Hopefully someone may be able to help me with a few questions I have about AGP stuff.
I was browsing through spec sheets of intel E7205 chipset last night and noticed there were two main sets of registers for the same things :
one set that concerns the Chipset Host Controler (device0)
one set that concerns the PCI-to-AGP Bridge (device1)
By looking in the intel-agp sources of AGPGART driver, I noticed all the intel chipsets that do not support agp 3.0 (i810... i850) use the first batch of registers to configure AGP device.
Now here is the deal... when looking through agp-via sources, I noticed there were two different sets of registers : one set for when AGP3.0 is activated, one set for when AGP3.0 is not activated.
So my question is this... When I use a card, that does not support AGP3.0 (i.e one that is not 8x enabled) on a slot that supports AGP3.0, what the hell is going on? Does it run in "AGP3.0 mode" or does it run in the previous mode?
Consequently, does the second set of registers concern the AGP3.0 mode and the first set of registers concern the AGP <3.0 mode ?
If yes, that would explain a lot of things, including why that god damn GraniteBay chipset is not working.
If only I could get my hands on some sort of spec sheets for AGP3.0 via chipsets that would help alot, I could compare it with registers used I guess. |
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hardware_chump
n00b
Joined: 16 Mar 2003
Posts: 7
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| Posted: Tue Mar 25, 2003 8:45 pm Post subject: |
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I'm am no expert on AGP 3.0 or Intel chipsets. But, I'll take a stab at answering your questions.
AGP 3.0 is not limited to 8x. AGP 3.0 has different protocol and signaling voltage levels. Typically, when a 1.5V AGP 2.0 card is inserted in a universal AGP 3.0 slot, the chipset will work in a backward compatibilty mode to support it.
I hope this helps. (I took a mindshare class on AGP last year.)
-hc |
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barlad
l33t
Joined: 22 Feb 2003
Posts: 673
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| Posted: Tue Mar 25, 2003 8:51 pm Post subject: |
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Ok thanks, any idea on the differences between the two sets of register please?
That's really what's getting on me... I need to understand why the hell there are two "APBASE", "ATTBASE", "ATTCTRL"... registers, each with different adress. |
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hardware_chump
n00b
Joined: 16 Mar 2003
Posts: 7
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| Posted: Tue Mar 25, 2003 8:57 pm Post subject: |
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Sorry, I think VIA keeps their datasheets NDA.
-hc |
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hardware_chump
n00b
Joined: 16 Mar 2003
Posts: 7
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