System Support

The PCI bus supports a bus master/target arbitration scheme. A bus master is a device that has been granted control of the bus for the purpose of initiating a transaction. A target is a device that is the recipient of a transaction. The Request (REQ), Grant (GNT), and FRAME signals are used by PCI bus masters for gaining access to the PCI bus. When a PCI device needs access to the PCI bus (and does not already own it), the PCI device asserts its REQn signal to the PCI bus arbiter (a function of the system controller component). If the bus is available, the arbiter asserts the GNTn signal to the requesting device, which then asserts FRAME and conducts the address phase of the transaction with a target. If the PCI device already owns the bus, a request is not needed and the device can simply assert FRAME and conduct the transaction. Table 4-2 shows the grant and request signals assignments for the devices on the PCI bus.

Table 4-2.

PCI Bus Mastering Devices

Device

REQ/GNT Line

Note

 

 

 

PCI Connector Slot 1

REQ0/GNT0

[1]

 

 

 

PCI Connector Slot 2

REQ1/GNT1

[1]

 

 

 

PCI Connector Slot 3

REQ2/GNT2

[2]

 

 

 

NOTE:

[1]SFF and CMT form factors only.

[2]CMT form factor only

PCI bus arbitration is based on a round-robin scheme that complies with the fairness algorithm specified by the PCI specification. The bus parking policy allows for the current PCI bus owner (excepting the PCI/ISA bridge) to maintain ownership of the bus as long as no request is asserted by another agent. Note that most CPU-to-DRAM accesses can occur concurrently with PCI traffic, therefore reducing the need for the Host/PCI bridge to compete for PCI bus ownership.

4.2.2 PCI Express Bus Operation

The PCI Express (PCIe) v1.1 bus is a high-performace extension of the legacy PCI bus specification. The PCI Express bus uses the following layers:

Software/driver layer

Transaction protocol layer

Link layer

Physical layer

Software/Driver Layer

The PCI Express bus maintains software compatibility with PCI 2.3 and earlier versions so that there is no impact on existing operating systems and drivers. During system intialization, the PCI Express bus uses the same methods of device discovery and resource allocation that legacy PCI-based operating systems and drivers are designed to use.

Transaction Protocol Layer

The transaction protocol layer processes read and write requests from the software/driver layer and generates request packets for the link layer. Each packet includes an identifier allowing any required responcse packets to be directed to the originator.

 

Technical Reference Guide

www.hp.com

4-3

Page 39
Image 39
HP dc7800 tower PCI Express Bus Operation, Software/Driver Layer, Transaction Protocol Layer, PCI Bus Mastering Devices

dc7800 tower specifications

The HP dc7800 Tower is a powerful desktop computer designed for professional and enterprise environments. Known for its stability, performance, and versatility, this model has secured its place in a variety of business settings. Launched in the mid-2000s, it embodies HP’s commitment to quality and innovation.

One of the main features of the HP dc7800 is its form factor. The tower configuration allows for easy upgrades and maintenance, providing ample space for additional hard drives, memory, and other components. This level of accessibility makes it ideal for businesses that need to adapt their systems to changing requirements.

The dc7800 is powered by Intel's Core 2 Duo processors, offering dual-core technology that enhances multitasking capabilities. With clock speeds ranging from 1.8 GHz to 3.0 GHz, this system can handle demanding applications with relative ease. It also supports Intel's vPro technology, which allows for remote management and security features, making it an excellent choice for organizations prioritizing IT control.

Another notable characteristic is the support for up to 8GB of DDR2 RAM. This allows for efficient data processing and improved performance when running multiple applications simultaneously. Additionally, the dc7800 features multiple storage options, accommodating both SATA hard drives and solid-state drives, which can significantly enhance boot times and overall system responsiveness.

Connectivity options on the HP dc7800 are robust. It includes a variety of USB ports, audio jacks, and optional legacy ports, ensuring compatibility with a wide range of peripherals and accessories. Networking capabilities are also prominent, with built-in Gigabit Ethernet providing high-speed internet access.

Furthermore, the desktop tower is designed with energy efficiency in mind. It meets ENERGY STAR certification standards, which not only helps reduce operational costs but also minimizes environmental impact.

Overall, the HP dc7800 Tower embodies a blend of performance, expandability, and energy efficiency, making it a reliable choice for businesses in need of a robust desktop solution. With its legacy of dependability and its suite of modern technologies, it continues to serve as a valuable asset in enterprise environments.