AVR-Chat

Yes, I saw that the Gumstix has an i2c boot-loader and was planning on
incorporating that into my doodad at some point.  I would consider a
boot-loader a relatively complex device.

Stateless is kind of hard to do when reading or writing a buffer.  The rest
of the commands can be stateless.  I suppose one can "write the buffer" then
issue the command to execute it.  That command could be a NOP if the buffer
had not been written, or, has been operated on and flushed...  Then each
transaction would be stateless.

I was looking at the SMBUS a bit, and will heed your advice to look at it
more carefully.  Thanks for the pointer.


-----------
Larry Barello
www.barello.net


| -----Original Message-----
| From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
| Of Dave Hylands
| Sent: Wednesday, February 15, 2006 9:30 PM
| To: AVR-Chat@yahoogroups.com
| Subject: Re: [AVR-Chat] I2C
| 
| Hi Larry,
| 
| On 2/15/06, Larry Barello <yahoo@barello.net> wrote:
| > Has anyone done an I2C interface to a complex device, like a graphic
| > display, or buffered serial I/O interface?  I am about to start
| designing
| > one and wanted any words of wisdom/architectural approaches other have
| to
| > offer before I start.
| 
| I just did a bootloader. Not quite as complicated as what you're
| looking at. It allows reading and writing of RAM, EEPROM and flash.
| 
| One thing to consider is to decide whether you want your commands to
| be self contained (stateless) or stateful. Some OS's (like linux) will
| issue an i2c command multiple times if it detects a failure. As these
| things go, it's possible for one side to think an error exists while
| the other side thinks that things are fine.
| 
| Using stateless commands means that you don't really care if the
| command is issued multiple times, it will do the exact same thing each
| time.
| 
| For example:
| 
| stateful: Use a register (in i2c parlance) to set an address. Read
| from another location and have the address auto-increment. This puts a
| bit less traffic on the i2c bus, but if one of your reads is reissued
| then the auto-increment will give the wrong data.
| 
| stateless: Pass the address that you want to read with the read
| request. Now if your command happens to get issued multiple times, you
| get the same data back each time.
| 
| > Because my doodad is both stand alone and a peripheral, I would like to
| make
| > all the primitives (graphic stuff mostly) available as I2C commands.  Is
| > this a reasonable thing to do?
| 
| I don't see why not.
| 
| I'd recommend taking a look at the SMBus spec as well. it defines some
| "standard" protocols for transferring data back and forth. I use the
| Block Process Call alot.
| 
| --
| Dave Hylands
| Vancouver, BC, Canada
| http://www.DaveHylands.com/
| 
| 
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