Bus Mastering

On high-bandwidth buses, a great deal of information flows through the channel every second. Normally, a processor is required to control the transfer rate of this information. In essence, the processor acts as a middleman that we should cut out to perform the transfer directly for more efficiency. This is done by having capable devices that take control of the bus and do the work themselves; referred to as bus masters. In theory, the processor can handle multiple tasks simultaneously; though in reality there are several complicating factors. In order to do bus mastering properly, a facility to arbitrate requests to "take over the bus" must exist, which is provided by the chipset. Bus mastering is also called a "1st party" DMA, since the work is controlled by the device doing the transfer.
Direct Memory Access (DMA) is the term used to refer to a transfer protocol where a peripheral device transfers information directly to or from memory, without the system processor being required. DMA has been used on the PC for years over the ISA bus, and for interface with devices such as sound cards and floppy disks. Conventional DMA uses regular DMA channels which are a standard system resource.
Currently, most bus mastering in the PC world is done on the PCI bus; additionally, support has been added for IDE/ATA hard disk drives to do bus mastering on PCI under certain conditions.
The following figure shows the PCI data acquisition process with and without the bus mastering function.

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Many of Advantech's data acquisition cards support the Bus mastering function. Usually used on high speed analog input channels, such as:
PCI bus: PCI-1712 series, PCI-1716 series, PCI-1714, PCI-1747U,
ISA bus: PCL-812PG, PCL-818L/LS, PCL-818HD, PCL-818HG.

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