Introduction
2=CA
Accelerated Graphics Port (4X AGP MODE)
The Accelerated Graphics Port (more commonly known as AGP) interface is a
new platform bus specification that enables high performance graphics
capabilities, especially 3D. This interface specification will enable 3D
applications, which not only require sufficient information storage so that the
monitor image may be refreshed, but also enough storage to support texture
mapping, z-buffering and alpha blending.
PCI will continue to be the main general-purpose system I/O bus. The AGP
interface has been designed specifically for dedicated use by graphics controllers,
and is not intended to replace PCI. It is physically separated from the PCI bus and
it uses a separate connector.
The benefits of AGP:
1. Direct texturing from main memory:
-Two memory pipes are provided to graphic engines for concurrency.
-Richer textures with no frame buffer growth.
-Graphics & CPU get a continuous view of graphic data structures from
GART (Graphics Address Re-mapping Table) Hardware.
2. De-multiplexed address and data.
-Enables pipelining and concurrency.
3. 533 Mbytes /s peak bandwidth. -Delivers high performance data control.
4. Peak bandwidth can be 4 times the PCI bus bandwidth, and higher sustained rates
via Sideband and pipelining.
5. Direct Memory Execute Textures.
6. Reduced Contention with the CPU and I/O devices for bus and memory access.
The PCI bus serves disk controllers, LAN chips, and possibly video capture.
AGP operates concurrently with and independent from most PCI operations.
Furthermore, the CPU can accesses system RAM while with the AGP graphic
chip reads RAM, because of out-of-order queuing hardware support in the chip
set. Therefore, in spite of the heavy access from the graphic chip, there should
be no audio breakup or other CPU degradation.
7. A separate port for the graphics chip to access memory, which allows for
concurrent texture reads from AGP memory while read/writing from local
memory. Efficient utilization of the bandwidths allows the graphic chip to
obtain 1.3 GB/s peak by using both ports simultaneously, versus 0.8 GB/s from
the local RAM.
8. Allowing the CPU to write directly to AGP shared system memory.