The HyperNews Linux KHG Discussion Pages

## DMA limits

  Forum: The Linux Kernel Hackers' Guide
  Re: DMA buffer sizes
  Keywords: DMA limit
  Date: Sat, 26 Jul 1997 02:16:07 GMT
  From: Albert Cahalan <acahalan at cs.uml.edu> <unknown>

    > I want to allocate a DMA buffer larger than 128*1024.
    > Is it possible to configure the kernel to allow bigger
    > DMA buffer sizes? I've attempted to increase the PAGE_SIZE
    > to 8192 but that crashes the system.
I hope that is not PC hardware! The ISA bus has a hard limit of 128 kB (16-bit DMA) or 64 kB (8-bit). Even 128 kB is hard though, because memory fragmentation makes it unlikely that you can allocate a contiguous 128 kB chunk under the 16 MB ISA DMA limit (or elsewhere).