On Mon, 28 Apr 2008 08:49:32 -0700 "Fargusson.Alan" <[EMAIL PROTECTED]> wrote:
> The DMA limit depends on the hardware. On 32 bit Intel DMA is limited to > 16M. On 64 bit Intel there is no limit. On Z the DMA limit is 2G. > > Note: the ISA bus isn't really the problem. The problem is that the DMA chip > only addresses 24 bits, although this is because the ISA bus was 24 bit. Not really ISA bus (legacy) devices are limited to 24bit DMA by the slave DMA controller (if used) and the number of address lines on the bus (if bus mastering) PCI devices generally depend on the device not the system so most are 32bit and more modern ones often 64bit (even on a 32bit mode box). Some are weird things like 26 or 28bit and 31bit is quite common as Windows used to have a 2GB physical limit once upon a time. For later systems it gets even more complicated as the AMD boxes have an IOMMU so 32bit devices can hit all of memory (but as the IOMMU window in most cases is itself above 0x80000000 31bit devices cannot use the IOMMU window). Alan ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
