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 4-1 shows the grant and request signals assignments for the devices on the PCI bus.

Table 4-1.

PCI Bus Mastering Devices

Device

REQ/GNT Line

 

 

PCI Connector Slot 1

REQ0/GNT0

 

 

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.

 

4-2

www.hp.com

Technical Reference Guide

Page 35 Page 37
Page 36
Image 36
HP dc5850 manual PCI Express Bus Operation, Software/Driver Layer, Transaction Protocol Layer, PCI Bus Mastering Devices
Page 35 Page 37

dc5850 specifications

The HP dc5850 is a desktop computer that was designed for business environments, offering a blend of performance, reliability, and efficiency. Released during the height of the mid-2000s, this system is powered by AMD processors, particularly the Athlon or Phenom series, which ensures that it can handle various computational tasks with ease.

The dc5850 features a compact chassis that adheres to the Microtower form factor. This design not only saves space but also allows for easier upgrades and maintenance. The unit typically supports a range of RAM configurations, with options for up to 8GB of DDR2 memory. This flexibility enables the user to tailor the system's performance according to their needs, whether for basic office tasks or more demanding applications.

Storage options on the HP dc5850 include a 3.5-inch HDD that can accommodate substantial data, with capacities typically ranging from 160GB to 1TB. The inclusion of a SATA interface ensures fast data transfer rates, which is essential for improving overall system performance. Moreover, the dc5850 boasts multiple USB ports, including USB 2.0 and sometimes even USB 3.0, facilitating easy connectivity with peripherals such as printers, scanners, and external drives.

Graphics capabilities on the dc5850 are generally provided by integrated solutions, although users have the option to add discrete graphics cards for enhanced performance in visual tasks. The system often comes with integrated audio, which supports basic multimedia needs without requiring additional sound cards.

In terms of connectivity, the HP dc5850 features built-in Ethernet for wired networking and may also offer options for Wi-Fi capabilities via PCI expansion slots. This makes it suitable for networked business environments, enabling seamless integration into office infrastructures.

The system is designed with energy efficiency in mind, complying with various environmental standards, thereby reducing its carbon footprint. This aspect may also lead to lower operational costs for businesses focused on sustainability.

Overall, the HP dc5850 stands out as a versatile desktop solution, catering to the essential needs of small to medium-sized businesses. With its combination of performance, expandability, and energy efficiency, it remains a noteworthy choice for users seeking reliable computing power in a compact and manageable form.
Top Page Image Contents