Re: Mapping Kernel-space to User-space

cjs (
Fri, 23 Jun 1995 21:01:48 -0500 (CDT)

> Hello,
> I am developing (together with Alessandro Rubini) a device driver (-module)
> for a laboratory interface quite popular in UK and Germany (and maybe else-
> where, too (the "1401" made by Cambridge Electronic Design). It supports
> such nice features like circular DMA on its ADC-channels or DMA-channels
> and is capable of some simple multitasking within its processor).
> Unlike most (all?) drivers the user should be able to allocate memory for
> DMA-purpose within his/her user-space via a malloc-like-call, as multiple
> DMA-buffers might be required, especially, if diffrent programs access the
> device simultaniously.

Something to remember is that on the braindead intels that we all know and
love, the DMA buffers need to be aligned on 4096 byte boundries and must
reside in the first 16M or so of memory (except for certain unique chipsets
and possibly anything made in the last year or so). In those latter cases
there are supposed to be special flags you need to set to get the DMA transfers
above the 16M marker.

You probably know this, but you didn't mention it, so I thought I'd
contribute! =)