computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, bus mastering is a feature supported by many bus architectures that enables a device connected to the bus to initiate direct memory access (DMA) transactions. It is also referred to as first-party DMA, in contrast with third-party DMA where a system DMA controller actually does the transfer. Some types of buses allow only one device (typically the

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

, or its proxy) to initiate transactions. Most modern bus architectures, such as PCI, allow multiple devices to bus master because it significantly improves performance for general-purpose

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

s. Some real-time operating systems prohibit peripherals from becoming bus masters, because the scheduler can no longer arbitrate for the bus and hence cannot provide deterministic latency. While bus mastering theoretically allows one peripheral device to directly communicate with another, in practice almost all peripherals master the bus exclusively to perform DMA to main memory. If multiple devices are able to master the bus, there needs to be a bus arbitration scheme to prevent multiple devices attempting to drive the bus simultaneously. A number of different schemes are used for this; for example SCSI has a fixed priority for each SCSI ID. PCI does not specify the algorithm to use, leaving it up to the implementation to set priorities.

References

How Bus Mastering Works
- Tweak3D

Brevard User's Group Computer buses Motherboard {{compu-hardware-stub

See also

References