so ... AGP { 1x, 2x } = PCI (o'really?) - Page 1
Forum section: electronics / general

author: DiTBho
author_rank: Super Contributor
timestamp: March 27, 2023, 04:36:04 pm
content: I've always wondered -was/is AGP only ever used for graphics cards?- (never seen ... say AGP-SCSI-HBA? AGP-optical-ethernet? ... )Foundthisinteresting answer

author: DiTBho
author_rank: Super Contributor
timestamp: March 27, 2023, 04:54:51 pm
content: I will buy an AGP(1)-PCI adapter to make good use of an - otherwise - unused AGP slot.(1) AGP 2x

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 27, 2023, 06:01:03 pm
content: Not same as PCI at all.The main reason these graphics buses existed (vesa, agp..) was to provide a dedicated bus, PCI shares its bandwidth with all devices, these don't.Then AGP 1.0 was already 2x faster than PCI.

author: DiTBho
author_rank: Super Contributor
timestamp: March 27, 2023, 06:25:31 pm
content: say,AGP = exclusive channelPCI = bustiming and signal protocol are similar... and =< AGP-2x electrical signals also seem compatibleQuote from: DavidAlfa on March 27, 2023, 06:01:03 pmbut this comment is exactly what I have always wonderedQuote(my evil plan is to make good use of a 2x AGP slot with a PCI-fpga card)

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 27, 2023, 06:49:06 pm
content: PCI works at 33MHz, AGP starts at 66, so no way.I guess you're making some kind of vintage adapter...?Otherwise, why using something so old?

author: DiTBho
author_rank: Super Contributor
timestamp: March 27, 2023, 08:18:31 pm
content: Quote from: DavidAlfa on March 27, 2023, 06:49:06 pmisn't the AGP clock "adaptable" to the board clock?66Mhz means ... PCI-X, good, but definitively it greatly reduces the number of devices I can use, and my pci-fpga card is clocked at 33Mhz.Quote from: DavidAlfa on March 27, 2023, 06:49:06 pmSupporting GNU/Linux on 2000-2008 RISC-boards.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 27, 2023, 09:04:39 pm
content: There's the opposite, AGP to PCI converters (Run AGP card in PCI slot):https://www.vogons.org/viewtopic.php?t=76665You might be lucky, apparently agp runs at 33MHz if not configured properly:https://wiki.osdev.org/AGPStill, it seems a long and painful journey!

author: ejeffrey
author_rank: Super Contributor
timestamp: March 30, 2023, 05:09:27 am
content: Quote from: DavidAlfa on March 27, 2023, 06:01:03 pmWell AGP was based on PCI, appeared to the host largely as a second PCI bus that happens to have only one device, and PCI existed with 66 MHz and 3.3V variants which were widely used in high performance systems, just not in mainstream desktops. AGP did have AGP specific transactions, including split read transactions (which were also added to PCI as part of PCI-X) and to access the AGP memory window which let the card use system memory for texture storage avoiding the need for lots of onboard memory. But AFAIK, only a few cards made heavy use of that, as memory costs dropped and the performance advantages of having on board texture memory were too great to ignore.Later revisions of AGP increased to speeds that PCI never supported, but it remained fundamentally based on PCI both at the physical and transaction model levels.