[ECOS] Device driver implementation questions

[ECOS] Device driver implementation questions

[Mike Sweeney]

I am finding the way device drivers are implemented in eCos to be
slightly confusing so was looking for some help. The main source of my
confusion is the need for some sort of interface under the io package
and then another part of the driver in the devs package. I have looked
at examples like the serial driver and understand how it works in that
context, but am having trouble seeing the bigger picture. Should
drivers for all types of devices follow this split implementation
design? Furthermore, can someone provide me an analogy between the
eCos driver model and Linux, for example? I don't see this two layer
method in Linux so am hoping someone can clarify this.

Thanks.

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[ECOS] Re: Device driver implementation questions

[Grant Edwards]

On 2007-06-14, Mike Sweeney <msweeney77@gmail.com> wrote:

> I am finding the way device drivers are implemented in eCos to be
> slightly confusing so was looking for some help. The main source of my
> confusion is the need for some sort of interface under the io package
> and then another part of the driver in the devs package. I have looked
> at examples like the serial driver and understand how it works in that
> context, but am having trouble seeing the bigger picture. Should
> drivers for all types of devices follow this split implementation
> design? Furthermore, can someone provide me an analogy between the
> eCos driver model and Linux, for example? I don't see this two layer
> method in Linux so am hoping someone can clarify this.

Linux has almost the exact same two layer method for many
drivers:

  Serial drivers: There is a line-discipline layer which
  provides the application with open/close/read/write calls.
  That corresponds to the "io" stuff in eCos. The
  line-discipline layer then calls lower-level
  hardware-specific drivers for different sorts of serial
  ports.  That corresponds to the "dev" stuff in eCos.

  SCSI drivers: Pretty much the same -- there's a generic layer
  that provides an API to the user and then a lower layer that
  talks to individual SCSI controllers (or other hardware).

There are probably other examples (VFS on top of the individual
filesystem modules, 80211 on top of various card drivers).  

-- 
Grant Edwards                   grante             Yow! FUN is never having to
                                  at               say you're SUSHI!!
                               visi.com            


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Re: [ECOS] Re: Device driver implementation questions

[Mike Sweeney]

On 6/14/07, Grant Edwards <grante@visi.com> wrote:
> On 2007-06-14, Mike Sweeney <msweeney77@gmail.com> wrote:
>
> > I am finding the way device drivers are implemented in eCos to be
> > slightly confusing so was looking for some help. The main source of my
> > confusion is the need for some sort of interface under the io package
> > and then another part of the driver in the devs package. I have looked
> > at examples like the serial driver and understand how it works in that
> > context, but am having trouble seeing the bigger picture. Should
> > drivers for all types of devices follow this split implementation
> > design? Furthermore, can someone provide me an analogy between the
> > eCos driver model and Linux, for example? I don't see this two layer
> > method in Linux so am hoping someone can clarify this.
>
> Linux has almost the exact same two layer method for many
> drivers:
>
>   Serial drivers: There is a line-discipline layer which
>   provides the application with open/close/read/write calls.
>   That corresponds to the "io" stuff in eCos. The
>   line-discipline layer then calls lower-level
>   hardware-specific drivers for different sorts of serial
>   ports.  That corresponds to the "dev" stuff in eCos.
>
>   SCSI drivers: Pretty much the same -- there's a generic layer
>   that provides an API to the user and then a lower layer that
>   talks to individual SCSI controllers (or other hardware).
>
> There are probably other examples (VFS on top of the individual
> filesystem modules, 80211 on top of various card drivers).
>
> --
> Grant Edwards                   grante             Yow! FUN is never having to
>                                   at               say you're SUSHI!!
>                                visi.com

Thanks for the information, that clarifies things for me.

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