HP XA Pipelining, Double clocking, sideband addressing, HP Kayak XA PC Workstations, Accelerated Graphics Port (AGP) Controller

2 System Board

Accelerated Graphics Port (AGP) Controller

Accelerated Graphics Port (AGP) Controller

The AGP technology was developed as a means to access system memory as a viable alternative to augmenting the memory of the graphics subsystem needed for high quality 3D graphics applications. All models of HP Kayak XA PC Workstations support an AGP (Accelerated Graphics Port) device (Laguna Graphic Controller from Cirrus).

The AGP bus is based upon a 66 MHz, 32 Bit PCI bus architecture, to which several signal groups have been added. These additional signals allow to implement AGP specific control and transfer mechanisms, which are:

•Pipelining and sideband addressing. These control mechanisms in- crease the bus efficiency compared to the PCI protocol.

•Double clocking (2x mode). This is a transfer mechanism that doubles the peak transfer rate to 528 MB/s, as two 32 Bit words are transferred in each clock period (2 x 32 bits x 66 MHz).

AGP specific transactions always use pipelining. The other two mechanisms can combine independently to pipelining, which leads to these operating modes:

•FRAME based AGP. Only the PCI protocol is used: 66 MHz, 32 Bits, 3.3V, 264 MB/s peak transfer rate.

•1 X AGP with pipelining, sideband addressing can be added: 66 MHz, 32 Bits, 3.3V, increased bus efficiency, 264 MB/s peak transfer rate.

•2 X AGP with Pipelining, sideband addressing can be added: 66 MHz dou- ble clocked, 32 Bits, 3.3V, increased bus efficiency, 528 MB/s peak trans- fer rate.

41