[Bug 1001397] I2C driver for Kinetis microcontrollers

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http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001397

--- Comment #60 from Ilija Kocho <ilijak@siva.com.mk> ---
Created attachment 2206
  --> http://bugs.ecos.sourceware.org/attachment.cgi?id=2206&action=edit
I2C driver print out actual frequency when trace enabled. Increment to
attachment 2188.

Mike

(In reply to comment #59)
> After setting CPU clock to 100Khz:
> 
> Freq        Mode         Meas
> 100Khz      Std          98Khz
> 100Khz      Agr          111Khz
> 400Khz      Std          363Khz
> 400Khz      Agr          416Khz

Thank you for the measurements.

> 
> From an application point of view, this is a little problematic, in that:
> 
> - When you set the goal and value, you don't get feedback in the
> configuration that tells you what the result will be. You have to get a
> scope and measure it.
> 
> - If you want to make it more accurate, you have to either guess the correct
> CPU clock, or reverse engineer the algorithm to calculate the required clock
> manually.
> 
> One solution might be to have the configuration calculate the proper CPU
> clock so you can then manually change the clock to get a better result. 
> 

It would be good to have this convenience in CDL but it requires some Tcl
programming, which requires some time...

The second best is to enable some printout at run-time. The attached
incremental patch enables printout of actual I2C clock frequency and period
when trace is enabled.

Note: The printouts that I got are pretty close to what you have measured for
100kHz, but there is a large discrepancy for 400kHz. Can you please and repeat
measurements and check the printouts?

> I am ok with committing the solution as is because I can figure it out for
> 100 and 400 and will have the only answers I need. I think it is just a
> question of how much you want to help the application programmer.

If you are happy with proposed patch and there aren't objections, I would
proceed with commit.

Ilija

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