Measurement Computing TempBook rev.3.0 - Manual (Page 127)

TempBook User’s Manual daqCommand Reference (Enhanced API) 11-3
daqAdcBufferRotate
DLL Function daqAdcBufferRotate(DaqHandleT handle, PWORD buf, DWORD scanCount, DWORD
chanCount, DWORD retCount);
C daqAdcBufferRotate(DaqHandleT handle, PWORD buf, DWORD scanCount, DWORD
chanCount, DWORD retCount);
Visual BASIC VBdaqAdcBufferRotate&(ByVal handle&, buf%(), ByVal scanCount&, ByVal chanCount&,
ByVal retCount&)
Delphi daqAdcBufferRotate(handle:DaqHandleT; buf:PWORD; scanCount:DWORD;
chanCount:DWORD; retCount:DWORD)
Parameters
handle Handle to the device for which the ADC transfer buffer is to be rotated
buf Pointer to the buffer to rotate
scanCount Total number of scans in the buffer
chanCount Number of channels in each scan
retCount Last value returned in the retCount parameter of the daqAdcTransferGetStat function
Returns DerrNoError - No error (also, refer to API Error Codes on page 11-39)
See Also daqAdcTransferGetStat, daqAdcTransferSetBuffer
Program References None
Used With All devices
daqAdcBufferRotate allows you to linearize a circular buffer acquired via a transfer in cycle
mode. This command will organize the circular buffer chronologically. In other words, it will order
the data from oldest-first to newest-last in the buffer. When scans are acquired using
daqAdcBufferTransfer
with a non-zero cycle parameter, the buffer is used as a circular
buffer; once it is full, it is re-used, starting at the beginning of the buffer. Thus, when the
acquisition is complete, the buffer may have been overwritten many times and the last acquired scan
may be any place within the buffer.
For example, during the acquisition of 1000 scans in a buffer that only has room for 60 scans, the
buffer is filled with scans 1 through 60. Then scan 61 overwrites scan 1; scan 62 overwrites scan 2;
and so on until scan 120 overwrites scan 60. At this point, the end of the buffer has been reached
again and so scan 121 is stored at the beginning of the buffer, overwriting scan 61. This process of
overwriting and re-using the buffer continues until all 1000 scans have been acquired. At this point,
the buffer has the following contents:
Buffer
Position
1 2 3 ... 39 40 41 42 ... 59 59 60
Scan 961 962 963 ... 999 1000 941 942 ... 958 959 960
In this case, because the total number of scans is not an even multiple of the buffer size, the oldest scan is
not at the beginning of the buffer and the last scan is not at the end of the buffer.
daqAdcBufferRotate
can rearrange the scans into their natural, chronological order:
Buffer
Position
1 2 3 ... 39 40 41 42 ... 59 59 60
Scan 941 942 943 ... 979 980 981 982 ... 998 999 1000
If the total number of acquired scans is no greater than the buffer size, then the scans have not overwritten
earlier scans and the buffer is already in chronological order. In this case, daqAdcBufferRotate does
not modify the buffer.
Note: daqAdcBufferRotate only works on unpacked samples.