[PARPORT] RE: DMA channel configuration

From: Chandan Mishra (Chandan.Mishra@efi.com)
Date: Mon Mar 20 2000 - 17:41:39 EST

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    > -----Original Message-----
    > From: Tim Waugh [mailto:twaugh@redhat.com]
    > Sent: Monday, March 20, 2000 1:49 PM
    > To: Chandan Mishra
    > Cc: linux-parport@torque.net
    > Subject: Re: DMA channel configuration
    > On Mon, 20 Mar 2000, Chandan Mishra wrote:
    > > I have a question which is not parallel port specific but
    > arose during
    > > the time while I was playing with parport driver. On PC how
    > is the dma
    > > channel autoconfigured if it is. As my understanding goes each
    > > peripherical controller is kind of hard wired to a particular dma
    > > channel of a dma controller (corect me if I am wrong). Then how does
    > > auto configuration works or how odes the driver discover the dma
    > > channel to use. Also how does peripheral auto-finds the available
    > > irqs.
    > For parallel ports: ECP chipsets just tell you this
    > information. You ask
    > the chipset what DMA channel and IRQ line it's using, and it
    > tells you.
    > It's theoretically possible to program it to use a DMA channel and IRQ
    > line of your choice, but I've never seen an implementation that allows
    > that.
    > For IRQs, see probe_irq_on and probe_irq_off.

    Well how can ECP chipsets discover which dma channel they should use. I mean
    isnt it set by jumpers or so, I mean isnt it hardwired. Can there be dynamic
    allocation dma channel. I mean if I am a peripheral controller, is it
    poosible for me to use one dma channel at one time and another at another
    time. Arent the dma channel already hardcoded on the board I mean in the way
    the connection from peripheral controller to hardware is.
    Please clarify for me. I know its kind of general pc hardware kind of
    question but I thought someone here might answer me.
    > Tim.
    > */

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