Editing Busdma (section)

{{Short description|Application programming interfaces for BSD operating systems}}
{{lowercase title}}
In [[computing]], '''busdma''', '''bus_dma''' and '''bus_space''' is a set of [[application programming interface]]s designed to help make [[device driver]]s less dependent on platform-specific code, thereby allowing the host [[operating system]] to be more easily [[portability (software)|ported]] to new computer hardware.{{r|usenix98|informit-2006}}  This is accomplished by having abstractions for [[direct memory access]] (DMA) mapping across popular machine-independent [[computer bus]]es like [[Peripheral Component Interconnect|PCI]], which are used on distinct architectures from [[IA-32]] (NetBSD/i386) to [[DEC Alpha]] (NetBSD/alpha).{{r|usenix98}}  Additionally, some devices may come in multiple flavours supporting more than one bus, e.g., [[Industry Standard Architecture|ISA]], [[Extended Industry Standard Architecture|EISA]], [[VESA Local Bus]] and [[Peripheral Component Interconnect|PCI]], still sharing the same core logic irrespective of the bus, and such device drivers would also benefit from this same abstraction.{{r|usenix98|p=§1.2|q=1.2.  Bus details}}  Thus the rationale of busdma is to facilitate maximum [[code reuse]] across a wide range of [[platform (computing)|platforms]].{{r|usenix98|p=§5|q=5.  Conclusions}}

Circa 2006, bus and DMA abstractions made it possible for NetBSD to support 50 hardware platforms and 14 CPU architectures out of a single source tree, compared to the [[Fork (software development)|fork]]ing model used by [[Linux]] ports.{{r|informit-2006}}

Originally implemented as the "bus_dma" APIs by the developers of the [[NetBSD]] operating system,{{r|usenix98|bus_dma}} busdma has been adopted by [[OpenBSD]], [[FreeBSD]] and their derivatives; with FreeBSD incorporating it under a '''busdma''' umbrella (without an underscore). Both NetBSD and OpenBSD have additional "bus_space" APIs{{r|bus_space}} that have been amalgamated into the version of busdma incorporated into FreeBSD. [[DragonFly BSD]] developers are also slowly converting their drivers to use busdma.