dma transfer rate using PCI-5112 with CVI

[ww]

Hi all,

for a high speed data aquisition using NI-PCI-5112 I measured the dma transfer speed. I can achive transfer rates between 28-29 MByte/s using the "niScope_FetchBinary"-functions of the niScopf-FP (with CVI). The transfer rate doesn't change when using the niScope_FetchBinary8, niScope_FetchBinary16, niScope_FetchBinary32 or niScope_FetchBinary-functions.

The PCI-bus uses 64 databits and 33 MHz bus clock. This should result in 33 x 4 MByte/s maximum transfer speed.

My questions:

• Does the dma transfer used by the niScope-driver uses only 8 bits from the 64 bit wide pci bus? This would explain the measured datarate.
• Is it possible to transfer up to 4 Bytes of measured data in one DMA cycle, allowing data transfer rates 4 times faster than the measured 28-29 Mytes/s?
• Is it possible to use the PCI-5112 in a 66MHz-PCI-slot instead of the normal 33 MHz-PCI-Slot? Are in this case higher transfer-rates possible?

Thanks in advance for any suggestions

Willi

[CarstenS]

Hi Willi,

I think the measured datarate can be explaind with this KB. It says that the acuired values will be scaled to a 64 bit floating point value.

Kind regards

Carsten

[DFGray]

If I remember correctly, the PCI-5112 uses 16 bits of the PCI bus for data transfer (not true for later models). It was originally designed in the late 1990s.  The rest of your difference is probably due to the fact that the PCI bus is shared by all the other devices on your system, as well.