User`s manual

Continuous Data Transfer 79
PCIS-DASK
Mechanisms
5 Continuous Data Transfer
The continuous data transfer function in the PCIS-DASK inputs or
outputs blocks of data to or from a plugged-in NuDAQ PCI device.
For input operations, the PCIS-DASK transfers the incoming data
to a buffer in the system memory. For output operations, the PCIS-
DASK transfers outgoing data from a buffer in the computer mem-
ory to the NuDAQ PCI device.
This chapter describes the mechanism and techniques that PCIS-
DASK use for continuous data transfer and the considerations for
selecting the continuous data transfer mode (synchronous or
asynchronous, double buffered, triggered or non-triggered mode).
5.1 Mechanisms
The PCIS-DASK uses two mechanisms to perform continuous
data transfer: interrupt transfer and DMA.
Interrupt transfer transfers data through the interrupt mechanism,
while the DMA controller chip performs data transfer via a hard-
ware. The PCIS-DASK uses the interrupt or DMA depending on
the device. When the device supports both mechanisms, the
PCIS-DASK decides on the data transfer method that takes maxi-
mum advantage of available resources. For example, PCI-9112
supports both interrupt and DMA for data transfers. The PCIS-
DASK uses DMA data transfer in this instance since it is faster.
For PCI-9111 that supports FIFO Half-Full and EOC interrupt
transfer modes, the PCIS-DASK uses the FIFO Half-Full interrupt
transfer mode since the CPU is interrupted to do data transfer only
when the FIFO becomes half-full.