Measurement-computing Data Acquisition Systems rev.10.4 Uživatelský manuál stáhnout pdf (Strana 121)

where mod is defined as the integer remainder of performing an integer divide of retCount by scanCount.

Detection of a buffer overrun condition is the responsibility of the application.

If using a linear buffer (DatmCycleOff) and the acquisition is expected to continue past the end of the

allocated buffer size, a new buffer must be allocated and configured using this function in a timely manner to

avoid loss of data (as would be the case in an alternating or “ping-pong” buffer approach).

Typical Transfer Buffer Settings

The following table shows a set of are typical transfer buffer settings; it assumes scan group size of 4 channels

and sample size of 2 bytes.

Desired Buffer

buf scanCount transferMask

Application allocated linear buffer of 50,000

scans updated on every sample

App pointer to memory

(size = 50,000 x 4 x 2

= 400,000 bytes)

50,000 DatmCycleOff +

DatmUpdateSingle +

DatmUserBuf

Application allocated linear buffer of 100,000

scans updated by block

App pointer to memory

(size = 100,000 x 4 x 2

= 800,000 bytes)

100,000 DatmCycleOff +

DatmUpdateBlock +

DatmUserBuf

Application allocated circular buffer of 40,000

scans updated on every sample

App pointer to memory

(size = 40000 x 4 x 2

= 320,000 bytes)

40,000 DatmCycleOn +

DatmUpdateSingle +

DatmUserBuf

Application allocated circular buffer of 200,000

scans updated by block

App pointer to memory

(size = 200,000 x 4 x 2

= 1,600,000 bytes)

200,000 DatmCycleOn +

DatmUpdateBlock +

DatmUserBuf

Driver allocated circular buffer of 40,000 scans

updated on every sample

NULL (Driver allocates

= 40,000 x 4 x 2

= 320,000 bytes)

40,000 DatmUpdateSingle +

DatmDriverBuf

Driver allocated circular buffer of 200,000 scans

updated by block

NULL (Driver allocates

= 200,000 x 4 x 2

= 1,600,000 bytes)

200,000 DatmUpdateBlock +

DatmDriverBuf

Prototypes

C/C++

daqAdcTransferSetBuffer(DaqHandleT handle, PWORD buf, DWORD scanCount,

DWORD transferMask);

Visual BASIC

VBdaqAdcTransferSetBuffer&(ByVal handle&, buf%, ByVal scanCount&, ByVal

transferMask&)

Program References

DAQADCEXO1.CPP, DAQADCEX02.CPP, DAQADCEX03.CPP, DAQADCEX05.CPP,

DAQADCEX07.CPP, DBK04EX.CPP, DBK07EX.CPP, DBK08EX.CPP, DBK09EX.CPP,

DBK12_13EX.CPP, DBK15EX.CPP, DBK16EX.CPP, DBK17EX.CPP, DBK18EX.CPP,

DBK19EX.CPP, DBK42EX.CPP, DBK43EX.CPP, DBK44EX.CPP, DBK45EX.CPP,

DBK50EX.CPP, DBK51EX.CPP, DBK52EX.CPP, DBK53_54EX.CPP, DAQEX.FRM (VB)

Programmer’s Manual 908594 Daq API Command Reference 4.2-65

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