Specifications

EP-BX7/BX7+
16
Accelerated Graphics Port (AGP)
The Accelerated Graphics Port (more commonly known as AGP) interface is a new
platform bus specification that enables high performance graphics capabilities, espe-
cially 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 concur-
rent 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
OVERVIEW