Measurement-computing Data Acquisition Systems rev.10.4 Uživatelský manuál stáhnout pdf (Strana 202)

Dynamic Waveform/Pattern Mode with Circular Buffer

If the waveform/pattern output mode has been defined to be dynamic (see daqDacSetOutputMode) and a

circular output transfer buffer is to be used, then the following will need to be performed to complete the

dynamic waveform/pattern output operation:

• Specify the output transfer buffer location and details with the daqDacWaveSetBuffer function.

The specified buf parameter must point to memory which has already been allocated by the

application prior to calling this function. The allocated buffer must be large enough to hold the

number of output updates for each channel required for the block of data to be transferred as

determined by the current waveform/pattern output channel configuration.

• Configure any waveform/pattern settings (such as update mode, trigger sources, frequency settings

that need to be configured

• Call the daqDacTransferStart function to download the output transfer buffer into the internal

waveform/pattern output FIFO on the device.

DacWaveSetTrig function. • Arm the waveform/pattern output by issuing the daq

• Trigger the waveform/pattern output (if necessary).

Monitor status of the dynamic waveform/pattern output calling the daqDacTransferGetS

function. The total amount of data transferred from the circular output transfer buffer to the

waveform/pattern output FIFO on the device will be returned in the retCount parameter. The

current position of the next data block to be written to the waveform/pattern output FIFO o

device can be calculated using the value of the retCount parameter. Please refer to the

daqDacTransfe

• tat

n the

rGetStat function for a complete discussion of calculating the current write

position pointer.

tered

. However, a

h have already been written but not updated. This function

Dyn

ed according to the output channel for which it will be output. Each update data block is ordered

as follows:

DAC0 DAC1 DAC2 DAC3 P3 DO

In general, the size allocated should be at least large enough to handle any delays that may be encoun

between buffer updates by the application without the buffer running completely empty. As the

waveform/pattern output progresses, the waveform/pattern output FIFO on the device will be filled by

emptying the unread data in the output transfer buffer. This value can vary, depending upon the ability of the

application to frequently update the buffer, and the update rate at which the outputs are clocked

good general rule is to make the size of the output transfer buffer at least that of the size of the

waveform/pattern output FIFO on the device.The filling of the output FIFO with data in the output transfer

buffer is performed automatically by the driver without checking whether the application has updated the

buffer. Therefore, the application needs to be aware of the current write position within the buffer, as well as

feeding new data updates to the buffer portions whic

should be called with the DdtmCycleOn flag set.

amic Output Transfer Buffer Organization

The output transfer buffer is organized into sequences of update data blocks. Each update data block represent

the sample data necessary to update all output channels configured for waveform/pattern output. The sample

data is order

If any of the above channels is not configured for waveform/pattern output, then it will simply not be included

in the update data block--however, the channel ordering will not change. If, for example, a waveform/pattern

output is configured for DAC0, DAC2 and P3 DO will have the following update data block:

DAC0 DAC2 P3 DO

4.4-20 Daq API Command Reference 908494 Programmer’s Manual

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