Re: i2c driver for at91sam7x

["Tom Deconinck" <t.deconinck@gmail.com>]

On Fri, Nov 7, 2008 at 5:14 PM, Andrew Lunn <andrew@lunn.ch> wrote:
>
> On Fri, Nov 07, 2008 at 08:39:23PM +0530, vibisreenivasan wrote:
> > hello,
> >       Is there any one working on i2c bus driver for at91sam7x.
>
> I know eCosCentric have one, but you need to pay for that.
>
> Other people have mentioned writing i2c drivers as well.
>
> However, you need to be careful. The i2c hardware is broken. The Linux
> kernel marks it as such. See:
>
> http://www.at91.com/samphpbb/viewtopic.php?t=4665&sid=1032a7cdc95b571dc784adb204d78d33
>
> From what i understand, if you are doing transfers of 1 byte, it is
> O.K, but multiple byte transfers can break.
>
> Writing a GPIO based driver should be reasonably easy as far as i
> understand and does not suffer from these problems.
>
>        Andrew

I have written such a driver some time ago, but I changed jobs since,
so I don't have access to the source anymore.
My experience: use GPIO and the eCos bit-banging interface, since the
hardware implementation is seriously broken.
The driver I wrote didn't work well using interrupts (latency problems
combined with a 'smart' hardware implementation that decides to
generate stop-conditions by itself, breaking multy-byte transfers,
etc.) It did work in polling mode.

Tom