PCI Bus Mastering

from:http://www.pcguide.com/ref/mbsys/buses/types/pciMastering-c.html

 

As discussed in the section on system bus functions andfeatures, bus mastering is the capability of devices on the PCI bus (other than thesystem chipset, of course) to take control of the bus and perform transfers directly. ThePCI bus is the first bus to popularize bus mastering; probably in part because for thefirst time there are operating systems and software that are really capable of takingadvantage of it.

PCI supports full device bus mastering, and provides bus arbitration facilities throughthe system chipset. PCI's design allows bus mastering of multiple devices on the bussimultaneously, with the arbitration circuitry working to ensure that no device on the bus(including the processor!) locks out any other device. At the same time though, it allowsany given device to use the full bus throughput if no other device needs to transferanything. In a way, the PCI bus acts like a tiny "local area network" inside thecomputer, in which multiple devices can each talk to each other, sharing a communicationchannel that is managed by the chipset.

 

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from:http://www.highpoint-tech.cn/china/technical_pc.htm

 

所谓 Bus Master 是具有存取记忆体或周边装置能力之装置，也就是Bus Master 的装置须有能力控制位址及控制讯号，PCI Bus Master 如果要以 Master Mode 存取资料，首先要经由REQ#控制讯号，向仲裁器发出要求，仲裁器会以GNT#控制讯号回应 PCI Bus Master 要求，PCI Bus Master 收到GNT#后，才取得Bus (总线)的使用权。Bus Master 可减少CPU的负荷，并增加系统的效能，因为当一装置在执行 Bus Master 的动作时， CPU 仍可执行其他的指令动作。