[MAGEEC] Chip variations: tests, results, and graphs
Alex J Lennon
ajlennon at dynamicdevices.co.uk
Sun Jul 27 17:18:02 BST 2014
Very interesting James. Do you mind me asking what the flash testing
comprised? e.g. read/write/erase cycles?
Best Regards,
Alex
On 27/07/2014 17:13, James Pallister wrote:
> Hi All,
>
> Some preliminary findings on variations in the ATMEGA328 chips.
>
> I've tested 28 chips. For each chip 9 tests were ran:
>
> flash0
> Test the area of flash 0x0800-0x0810
> flash1
> Test the area of flash 0x080C-0x081C
> flash2
> Test the area of flash 0x08FC-0x090C
> flash3
> Test the area of flash 0x0FFC-0x100C
> ram0
> Repeatedly access 0x0000 - 0x0020
> ram1
> Repeatedly access 0xF007 - 0xF017
> alu
> Perform combinations of mul, fmul, inc and dec
> nop
> Lots of nops
> branch
> Repeatedly branch randomly in low flash
>
>
> Each test was run 8 times, and outliers excluded. All were run in the
> same harness, with the same crystal, resistors, etc.
>
> Results across each test. These show the distributions of the
> measurements taken, where the distribution consists of the 28 chips.
>
>
> From the first graph: there is a significant different, even on a day
> to day basis. I'm not sure what causes this - I'd expect the power to
> be lower at lower temperatures, which we don't see.
>
> For each chip:
>
> Mean power for each chip:
>
>
>
> The average power changes quite a lot, going from < 80mW to > 100mW.
> In almost all cases, the average power was higher on Saturday - not
> sure why this is, the temperature difference was only 3-4 degrees (and
> I'd expect the temperature to go down with lower temperature).
>
> The chips tend to vary as a whole, e.g. rather than the ALU varying
> significantly in one part rather than another. The following graph
> marks the average power for each test, divided by test type (different
> color/marker combinations) per chip. This should allow hopefully allow
> us to do a calibration run first.
>
> Legend for the above graph:
> Blue cross
> ram1
> Red star
> ram0
> Green plus
> alu
> Black plus
> flash3
> Green cross
> flash2
> Blue star
> flash1
> Red plus
> flash0
> Black star
> nop
>
>
>
> Any thoughts / ideas for more tests are welcome.
>
>
> James
>
>
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