gumstix

Hi David,

On Sat, 19 Mar 2005 16:48:01 -0800 (PST), David Farrell
<davidjf2001@...> wrote:
> Two masters cannot talk to each other. 

Sure they can. What makes you think that they can't? The master
normally sits in slave-receive mode and switches into master-transmit
when it wants to send something.

> What you
> are describing requires a bus bridge. I don't
> know of one that exists for I2C.  

Not required.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

Hi Dave,

If the pxa loses arbitration and switches into slave-receive mode or
if it is sitting on the line in slave-receive mode, the linux driver
has to read the data on the sda line.  Do you know if this is already
implemented in the driver?  I was under the impression that the
interface for master-receive would only receive data requested by the
command, not the data received while it was waiting to gain
arbitration.

Thanks,
Chander


On Sat, 19 Mar 2005 16:53:10 -0800, Dave Hylands <dhylands@...> wrote:
> Hi David,
> 
> On Sat, 19 Mar 2005 16:48:01 -0800 (PST), David Farrell
> <davidjf2001@...> wrote:
> > Two masters cannot talk to each other.
> 
> Sure they can. What makes you think that they can't? The master
> normally sits in slave-receive mode and switches into master-transmit
> when it wants to send something.
> 
> > What you
> > are describing requires a bus bridge. I don't
> > know of one that exists for I2C.
> 
> Not required.
> 
> --
> Dave Hylands
> Vancouver, BC, Canada
> http://www.DaveHylands.com/
> 
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Isn't this a master talking to a slave then?
By putting a ram in common to two masters you
don't need any slave code.

David.

--- Dave Hylands <dhylands@...> wrote:
> Hi David,
> 
> On Sat, 19 Mar 2005 16:48:01 -0800 (PST), David
> Farrell
> <davidjf2001@...> wrote:
> > Two masters cannot talk to each other. 
> 
> Sure they can. What makes you think that they
> can't? The master
> normally sits in slave-receive mode and
> switches into master-transmit
> when it wants to send something.
> 
> > What you
> > are describing requires a bus bridge. I don't
> > know of one that exists for I2C.  
> 
> Not required.
> 
> -- 
> Dave Hylands
> Vancouver, BC, Canada
> http://www.DaveHylands.com/
> 
> 
>
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Hi David,

> Isn't this a master talking to a slave then?
> By putting a ram in common to two masters you
> don't need any slave code.

Ahh - I get what you're talking about. Yeah - if two devices which are
acting as masters (at the same moment in time) try to communicate with
each other, one of them will lose arbitration. The loser switches into
slave mode and can continue to receive the message.  Since they were
talking to each other, then they MUST have been exchanging address
bytes when the arbitration loss occurs.

The loser would have to resend it's message once the winner finished.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/

I agree that using RAM or another device as a buffer to communicate
between two master devices is possible.  My argument against this is
that it is not a clean solution and takes some time to setup the
hardware and software.  This time could be spent working on a clean
solution such as enabling slave operation of one of the micro
controllers.

Chander


On Wed, 23 Mar 2005 07:08:57 -0800, Dave Hylands <dhylands@...> wrote:
> Hi David,
> 
> > Isn't this a master talking to a slave then?
> > By putting a ram in common to two masters you
> > don't need any slave code.
> 
> Ahh - I get what you're talking about. Yeah - if two devices which are
> acting as masters (at the same moment in time) try to communicate with
> each other, one of them will lose arbitration. The loser switches into
> slave mode and can continue to receive the message.  Since they were
> talking to each other, then they MUST have been exchanging address
> bytes when the arbitration loss occurs.
> 
> The loser would have to resend it's message once the winner finished.
> 
> --
> Dave Hylands
> Vancouver, BC, Canada
> http://www.DaveHylands.com/
> 
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I don't know what a clean solution is. As I
understood the problem there where boards with
master software only. Of course if the slave
drivers existed for either one, there is no
issue.
A ram on a common bus with two (or more!) masters
functions as a mailbox type of device. No
additional software.

David.

--- Chander S <inetorders@...> wrote:
> I agree that using RAM or another device as a
> buffer to communicate
> between two master devices is possible.  My
> argument against this is
> that it is not a clean solution and takes some
> time to setup the
> hardware and software.  This time could be
> spent working on a clean
> solution such as enabling slave operation of
> one of the micro
> controllers.
> 
> Chander
> 
> 
> On Wed, 23 Mar 2005 07:08:57 -0800, Dave
> Hylands <dhylands@...> wrote:
> > Hi David,
> > 
> > > Isn't this a master talking to a slave
> then?
> > > By putting a ram in common to two masters
> you
> > > don't need any slave code.
> > 
> > Ahh - I get what you're talking about. Yeah -
> if two devices which are
> > acting as masters (at the same moment in
> time) try to communicate with
> > each other, one of them will lose
> arbitration. The loser switches into
> > slave mode and can continue to receive the
> message.  Since they were
> > talking to each other, then they MUST have
> been exchanging address
> > bytes when the arbitration loss occurs.
> > 
> > The loser would have to resend it's message
> once the winner finished.
> > 
> > --
> > Dave Hylands
> > Vancouver, BC, Canada
> > http://www.DaveHylands.com/
> > 
> >
>
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> >
>
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> >
> 
> 
>
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