Subject: Re: New i2c framework
To: Jason Thorpe <>
From: Eduardo Horvath <eeh@NetBSD.ORG>
List: tech-kern
Date: 07/31/2003 21:09:54
On Thu, Jul 31, 2003 at 08:53:02AM -0700, Jason Thorpe wrote:
> On Thursday, July 31, 2003, at 08:43  AM, Eduardo Horvath wrote:
> >Ick.  So instead of issuing one command to an intelligent I2C 
> >controller
> >you need to issue a dozen commands.  Doesn't that sort of defeat the
> >purpose of having an intelligent I2C controller?
> The intelligent controllers that I have encountered don't support this 
> in any case.  The ones I have used basically support this:
> 	- START [write]
> 	- send address
> 	- send command byte [optional]
> 	- send command byte [optional]
> 	- read byte
> 	- read byte [optional]
> 	...
> i.e. no support for sending REPEATED START between the individual byte 
> reads.  I also haven't encountered devices that require this, either.  
> The ones that return multiple data bytes simply keep sending them until 
> they see NACK from the master.
> Do you have examples of devices that require the behavior you're 
> talking about?

I have personally dealt with devices that require repeated starts
between data byte transfers, but I don't recall the specific part
numbers at the moment.  I expect this will be a large issue when
you move away from EEPROMs and RTC devices.