I saw this article while searching for a compatable 1394B I/O card. It was
relevent to digital cameras locking up XP64 when processing large DMA
transfers. I am moving to XP64 to use the increased RAM for digital audio
recording. Can anyone shed light on whether or not this should be a concern?
I was going to purchase a system with 8 meg of RAM. TIA!
Mike (mgremlin)
-----------------
http://www.ptgrey.com/support/kb/index.asp?a=4&q=253
The following problem affects 64bit versions of both Windows XP and the
upcoming release of Vista.
One of the primary reasons for moving towards 64bit operating systems is to
increase the maximum amount of memory that can be installed on a system
beyond the 4GB limit of 32bit machines. Experimentation has revealed that,
despite the ability to install and configure much larger amounts of memory on
these machines, attempting to use devices that perform large DMA transfers
will cause undesirable behavior - primarily system crashes (BSOD, or blue
screen of death).
The issue is that machines with at least 4GB of RAM have access to 256 or
fewer memory map registers. Map registers are required for DMA'ing data into
the main memory of the computer. One register is required for each memory
page. Each memory page is 4096 bytes. Thus, in order to DMA a 4096000 byte
image, 1000 memory map registers would be required.
Each map register consumes 4K from non-paged memory. The OS will allocate no
more than a hard coded 256K to a device.
Based on the current limitations of 64 bit Windows XP, a system with 4GB of
RAM (256 memory map registers) could theoretically interface with a camera
that produces 256*4096 = 1048576 byte images (1MB) without any troubles.
Pending further qualification, it appears as though even this configuration
will not work in practice on all 64bit platforms - problems have been
observed with cameras with many different image sizes smaller than 1MB.
This problem does not happen on 64bit systems with less than 4GB of RAM
because the OS can address the memory with 32 bit DMAs via a set of "virtual"
map registers.
If this behavior is observed, the only short term fix is to reduce the
amount of memory on the system in question to below 4GB. However, Point Grey
Research is actively working on a solution to this issue using the
proprietary FlyCapture software and drivers.