Ultra Fast Multiscalers / Questions and Answers

Concerning P7889 and DMA: the manual makes a point that we should use DMA and maybe even increase the blocksize to 32678. If we enable DMA, less start events than sweeps are counted. Is DMA mode incompatible with Windows 7-64 bit?

DMA: the actual software has a built-in automatic control for using DMA and adapting the buffer size, that can be disabled by a line "autodma=0" in the P7889.INI file. When this line is not commented out, DMA can be selected by a checkbox in the settings dialog. Otherwise acquisition starts first in DMA mode and if the count rate is low DMA will be disabled. DMA should be used for count rates higher than about 200 kHz. DMA should be disabled for count rates lower than about 50 kHz and this is done by the automatic control. Otherwise it takes a long time to fill the event buffer and the thread receiving the buffer could run into the DMA timeout of 2 sec before any data can be evaluated. So it may appear that there are less starts than sweeps as the sweep counter counts immediately whereas the start counts are delayed.

There is no difference at all in the software between 32-bit and 64-bit, the native 64-bit software uses the same source code and is just compiled using another compiler. In principle a 64-bit Windows runs faster and more stable than a 32-bit Windows.

Ultra Fast Multiscalers