3.2 Simultaneous acquisition and readout (CST option)
40
Acqiris SA230E User's Manual
Output data streams
Acquired data stream per channel
Acquired samples are in 14-bit format but 32-bit data are streamed in output.
When reading data, each int32 data returned by the function
FetchDataInt32
contains 14-bit raw
data, mapped on 16-bits and left aligned.
The
NbOfElementsToFetch
should verify:
NbOfElementsToFetch = NbOfSamplesToFetch /
2
About the number element to fetch: the element represents a number of Int32 of data or markers. For
example:
AqMD3_StreamFetchDataInt32(session, "StreamCh1", numElementsToFetch,
elements.size(), elements.data(),&availableElements, &actualElements,
&firstValidElement);
Where:
- StreamCh1/StreamCh2
: definesthe channel to fetch.
- numElementsToFetch
: defines the minimum number of Int32 data to be fetched. It must be a
multiple of 16.
- availableElements
: returns the number of Int32 data already acquired and available to be
fetched on-board.
- actualElements
: returns the number of Int32 data fetched in the current call. This number is
always <= numElementsToFetch.
- firstValidElement
: represents the first valid Int32 element in the returned data buffer. It is
used for data alignment reasons.
- elements
: contains the int32 data returned by the function.
When fetching the data stream, each int32 contains 2x 14-bit raw data, mapped on 16-bits and left
aligned. For example:
element[0]
contains
sample_0
and
sample_1
,
element[1]
contains
sample_2
and
sample_3
, etc....
Marker stream (absolute trigger position)
The marker stream contains the trigger time-stamps, encoded in 512 bits, as described below.
511
96
95
32
31
8
7
0
Reserved for future use
Trigger position
Trigger index
0x01
Table 3.1
- Trigger time-stamp fields.
The trigger position in number of samples is given by:
Returned Trigger position
/ 256
The trigger position in seconds is given by:
Returned Trigger position
/ (256 x
Sampling rate
)
Trigger position
Using raw data output, trigger position is known with the accuracy of a sample (corresponding to the
1
st
sample). If customer application requires trigger position at sub-sample, the information is available
on the marker stream (absolute trigger position).
Acquisition sequence
An example of CST acquisition sequence is illustrated below.
