
Chapter 4
Programming
©
National Instruments Corporation
4-55
In dual channel DMA, two buffers are allocated, one for each DMA
channel. Initially, one channel transfers data. When it issues a TC, hardware
circuitry in the AT E Series board automatically switches to the other
channel, which is previously programmed. In the meantime, the first
channel is reprogrammed and kept ready so that, when the second channel
issues TC, the AT E Series board switches back to the first channel. When
one buffer is being serviced, the CPU can access the other buffer. This way,
seamless data transfer is possible.
Dual-channel DMA can be used in analog output, or for the general purpose
counter/timers. Only the AT-MIO-16E-1 supports dual-channel DMA for
analog input. Notice that in analog output when a single DMA channel is
serving both DACs, the buffer must contain interleaved data, meaning that
every other word is written to a DAC. In dual channel DMA, there is one
buffer for each DMA channel and within each buffer data is interleaved.
Also notice that whenever a TC interrupt is generated, the corresponding
DMATCCLR bit in the Strobes Register (address 0x01) must be strobed.
This clears the TC status bits for that logical DMA channel.
Содержание AT-MIO E Series
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