CompuScope SDK Manua.. - Egmont Instruments

Appendix A
Comparison of Various
Data Transfer Routines
Buffered Access Routines
All buffered routines read a block of data from CompuScope on-board memory; achieving high data
transfer rates and thus allowing significant optimization of application performance. However, most
buffered routines have access to only one CompuScope A/D converter's memory at a time. Therefore, in
single channel mode, these routines will read only the odd or the even samples. The two buffers must be
interleaved later by the user applications. In dual channel mode no interleaving is necessary, since each
A/D converter's memory holds the data from a separate input channel. The only exception is the
gage_transfer_buffer_3 routine which, when called in single channel mode, automatically downloads the
data from both A/D converters' memories and does the interleaving within the drivers.
The gage_transfer_buffer and gage_trigger_view_transfer routines provide a CPU mediated data
transfer (i.e., a transfer where the CPU acts as mediator between host memory and the CompuScope
board). The only difference between the two routines is in how the addresses for data to be downloaded
are specified. gage_transfer_buffer transfers data starting from the absolute address given as one of the
parameters. By contrast, gage_trigger_view_transfer transfers data starting from a reference address
position. This reference address is available in the trigger_view_offset global driver variable, which is set
by the function set_trigger_view_offset. For both the gage_transfer_buffer and
gage_trigger_view_transfer routines, the user application must allocate and provide a host buffer of
sufficient size to hold the requested data.
For PCI (CP500) CompuScopes, there is no intrinsic limitation on the amount of data that can be
transferred at a time by gage_trigger_view_transfer. However, the gage_trigger_view_transfer routine
can only transfer 4 KSamples at a time on ISA bus CompuScopes. Several of these transfers can be
chained together using the gage_set_trigger_view_offset routine to form one larger transfer, as shown
below:
offet = 0;
position = 0;
while (depth > 0)
{
if (depth > 4096)
transfer_depth = 4096;
else
transfer_depth = depth;
gage_set_trigger_view_offset (offset);
gage_trigger_view_transfer (GAGE_CHAN_A, (int16*) (buffer+position), transfer_depth);
depth -= transfer_depth;
CompuScope API Reference Manual 94