Re: Controlling HD44780 LCD via I2C-GPIO-Expander?

[Jeff Sutherland <jeffs@xxxxxxxxxxxxxxxxxx>]

On Tuesday 16 June 2009, Conrad Braun wrote:
> Hello,
>
> I'm currently trying to control an LCD via a PCF8574 I2C GPIO expander.
> It looks as if I'm running into timing problems on an AT91RM9200 conitec
> board with the I2C_GPIO driver and kernel 2.6.28; there is a delay of
> almost 8ms between every byte sent over the I2C bus. Is this possibly an
> effect of using the I2C_GPIO driver, or am I looking at the wrong suspect?
> I haven't found any hints on this matter in the mailing list archives or
> the web, though, so maybe there's another problem. I'm out of clues, tbh,
> and any help is appreciated.
>
> Thanks,
>  Conrad

The I2C_GPIO driver in itself is probably not to blame, although using a 
hardware I2C uart will be faster.  What is the clock frequency you've 
selected?  What kind of messaging are you using?  For the best performance 
trying to send multi-byte messages it's probably best to use the low level 
I2C interface by formatting the message into a buffer then sending it out 
using the 'ioctl(<i2c_device>,I2C_RDWR,&buffer);'

-Jeff
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