On Wed, 19 Sep 2001, David Olofson wrote:
> On Tuesday 18 September 2001 18:40, Calin A. Culianu wrote:
> > > On Monday 10 September 2001 16:48, S. Ancelot wrote:
> > > > Hi,
> > > > 1. Is it possible to write a single PCI I/O driver module that can
> > > > be accessible from user or kernel space ?
> > >
> > > Yes, but it's not trivial to do it in a "nice" way.
> > >
> > > (The "DPI" I hacked when I used RTL for real time audio replaced the
> > > kernel driver "API" with calls that automatically detected the
> > > calling context and used Linux or RTL calls accordingly.)
> > >
> > > > 2. on the PCI board, I use , I would like to remap I/O pci to have
> > > > direct memory access from user space programs directly.
> > > > is it possible and how ?
> > >
> > > Nice Linux specific feature: Use "ioperm()" to gain access to the
> > > ports you need. Then use port instructions (or macros) right in your
> > > code, as if you were running in kernel space - or under DOS. :-)
> >
> > Wait.. but how can one do DMA this way?
>
> You can't, AFAIK. You need a kernel driver for setting up the DMA. You'll
> probably also need it to handle the IRQ for DMA to be truly useful.
>
>
> > Won't the whole virtual,
> > swappable, transient nature of user memory basically cause problems
> > when trying to use DMA?
>
> No, not even if you share the buffer with user space applications, as for
> example most (modern) sound card drivers can do if you request it. DMA
> buffers are always locked, and should also be allocated with flags that
> ask for memory in the accessible range for the hardware in question.
> (Busses have different DMA adressing limits.)
>
> BTW, you *can* prevent user space code, data and stack from being swapped
> out if you want. (Very useful with Linux/lowlatency, as swapped memory
> out is the only way that the system can still cause SCHED_FIFO threahs to
> miss deadlines on lowlatency kernels.) See mlock() and mlockall().
Right, mlock() is the call i believe. Very useful indeed...
-Calin
>
>
> //David Olofson --- Programmer, Reologica Instruments AB
>
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> | A Free/Open Source Plugin API for Professional Multimedia |
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