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(c) Spectrum Instrumentation GmbH
Standard Single acquisition mode
Acquisition modes
Example of data transfer
To keep the example simple it does no error checking. Please be sure to check for errors if using these command in real world programs!
Users should take care to explicitly send the M2CMD_DATA_STOPDMA command prior to invalidating the
buffer, to avoid crashes due to race conditions when using higher-latency data transportation layers, such
as to remote Ethernet devices.
Standard Single acquisition mode
The standard single mode is the easiest and mostly used mode to acquire analog data with a Spectrum acquisition card. In standard single
recording mode the card is working totally independent from the PC, after the card setup is done. The advantage of the Spectrum boards is
that regardless to the system usage the card will sample with equidistant time intervals.
The sampled and converted data is stored in the on-board memory and is held there for being read out after the acquisition. This mode allows
sampling at very high conversion rates without the need to transfer the data into the memory of the host system at high speed.
After the recording is done, the data can be read out by the user and is transferred via the bus into PC memory.
This standard recording mode is the most common mode for all
analog and digital acquisition and oscilloscope boards. The data
is written to a programmed amount of the on-board memory (mem
-
size). That part of memory is used as a ring buffer, and recording
is done continuously until a trigger event is detected. After the trig
-
ger event, a certain programmable amount of data is recorded
(post trigger) and then the recording finishes. Due to the continuous
ring buffer recording, there are also samples prior to the trigger
event in the memory (pretrigger).
When the card is started the pre trigger area is
filled up with data first. While doing this the board’s trigger detection is not armed. If you use a huge pre
trigger size and a slow sample rate it can take some time after starting the board before a trigger event will
be detected.
Card mode
The card mode has to be set to the correct mode SPC_REC_STD_SINGLE.
Memory, Pre- and Posttrigger
At first you have to define, how many samples are to be recorded at all and how many of them should be acquired after the trigger event
has been detected.
You can access these settings by the register SPC_MEMSIZE, which sets the total amount of data that is recorded, and the register SPC_POST
-
TRIGGER, that defines the number of samples to be recorded after the trigger event has been detected. The size of the pretrigger results on
the simple formula:
pretrigger = memsize - posttrigger
The maximum memsize that can be use for recording is of course limited by the installed amount of memory and by the number of channels
to be recorded. Please have a look at the topic "Limits of pre, post memsize, loops" later in this chapter.
void* pvData = pvAllocMemPageAligned (1024);
// transfer data from PC memory to card memory (on replay cards) ...
spcm_dwDefTransfer_i64 (hDrv, SPCM_BUF_DATA, SPCM_DIR_PCTOCARD , 0, pvData, 0, 1024);
spcm_dwSetParam_i32 (hDrv, SPC_M2CMD, M2CMD_DATA_STARTDMA | M2CMD_DATA_WAITDMA);
// ... or transfer data from card memory to PC memory (acquisition cards)
spcm_dwDefTransfer_i64 (hDrv, SPCM_BUF_DATA, SPCM_DIR_CARDTOPC , 0, pvData, 0, 1024);
spcm_dwSetParam_i32 (hDrv, SPC_M2CMD, M2CMD_DATA_STARTDMA | M2CMD_DATA_WAITDMA);
// explicitely stop DMA tranfer prior to invalidating buffer
spcm_dwSetParam_i32 (hDrv, SPC_M2CMD, M2CMD_DATA_STOPDMA);
spcm_dwInvalidateBuf (hDrv, SPCM_BUF_DATA);
vFreeMemPageAligned (pvData, 1024);
Register
Value
Direction
Description
SPC_CARDMODE
9500
read/write
Defines the used operating mode, a read command will return the currently used mode.
SPC_REC_STD_SINGLE
1h
Data acquisition to on-board memory for one single trigger event.
Register
Value
Direction
Description
SPC_MEMSIZE
10000
read/write
Sets the memory size in samples per channel.
SPC_POSTTRIGGER
10100
read/write
Sets the number of samples to be recorded per channel after the trigger event has been detected.
Image 51: standard acquisition mode and pretrigger/posttrigger/trigger relation
Содержание M2p.59 Series
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