Arne Vidstrom explains how dumping a PC's main memory over FireWire could cause the Memory Controller Hub of an Intel chipset to hang.
According to Arne Vidstrom the problem occurs while dumping the Upper Memory Area(UMA) , specifically the memory region from the graphics adapter card (0xc0000) to the end of the first MB at 0xfffffh. This part of the physical address space usually contains ROM BIOS extensions but could also be mapped to main memory.
Arne Vidstrom now describes a certain situation which will lead to an implicit writeback from the Memory Controller Hub (MCH) to the I/O Controller Hub (ICH). This will hang the MCH because it has not been designed for that situation.
To work around the problem, Vidstrom recommends to skip the UMA when imaging a PC's main memory.
