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One of the major improvements the PCI Local Bus had over other I/O architectures was its configuration mechanism. In addition to the normal memory-mapped and I/O port spaces, each device function on the bus has a configuration space, which is 256 bytes long, addressable by knowing the eight-bit PCI bus, five-bit device, and three-bit function numbers for the device (commonly referred to as the ...
Burst reads (using linear incrementing) are permitted in PCI configuration space. Unlike I/O space, standard PCI configuration registers are defined so that reads never disturb the state of the device. It is possible for a device to have configuration space registers beyond the standard 64 bytes which have read side effects, but this is rare. [31]
The beginning of this structure is marked by the 4 byte ASCII signature PCIR and a pointer to this is stored at offset +18h as a 2 byte little endian value. [6] This allows it to scan the PCI configuration space to find the correct device and BARs it needs to use.
The distinction can be arbitrary between a computer bus, often closer in space, and larger telecommunications networks. Many device interfaces or protocols (e.g., SATA, USB, SAS , PCIe ) are used both inside many-device boxes, such as a PC, and one-device-boxes, such as a hard drive enclosure .
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
The PCI-X standard was developed jointly by IBM, HP, and Compaq and submitted for approval in 1998. It was an effort to codify proprietary server extensions to the PCI local bus to address several shortcomings in PCI, and increase performance of high bandwidth devices, such as Gigabit Ethernet, Fibre Channel, and Ultra3 SCSI cards, and allow processors to be interconnected in clusters.
TDATA_WIDTH must be an integer number of bytes and is recommended to be 8, 16, 32, 64, 128, 256, 512 or 1024-bits. TSTRB: Transmitter: TDATA_WIDTH/8: TSTRB is the byte qualifier that indicates whether the content of the associated byte of TDATA is processed as a data byte or a position byte. TKEEP: Transmitter: TDATA_WIDTH/8
Configuration space may refer to: . Configuration space (physics) Configuration space (mathematics), the space of arrangements of points on a topological space PCI configuration space, the underlying way that the Conventional PCI, PCI-X and PCI Express perform auto configuration of the cards inserted into their bus