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Very interesting James. Do you mind me asking what the flash testing
comprised? e.g. read/write/erase cycles?<br>
<br>
Best Regards,<br>
<br>
Alex<br>
<br>
<div class="moz-cite-prefix">On 27/07/2014 17:13, James Pallister
wrote:<br>
</div>
<blockquote cite="mid:53D5251A.60706@bristol.ac.uk" type="cite">
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Hi All,<br>
<br>
Some preliminary findings on variations in the ATMEGA328 chips.<br>
<br>
I've tested 28 chips. For each chip 9 tests were ran:<br>
<br>
<table cellpadding="2" cellspacing="2" width="733" border="1"
height="58">
<tbody>
<tr>
<td valign="top">flash0<br>
</td>
<td valign="top">Test the area of flash 0x0800-0x0810<br>
</td>
</tr>
<tr>
<td valign="top">flash1<br>
</td>
<td valign="top">Test the area of flash 0x080C-0x081C</td>
</tr>
<tr>
<td valign="top">flash2<br>
</td>
<td valign="top">Test the area of flash 0x08FC-0x090C</td>
</tr>
<tr>
<td valign="top">flash3<br>
</td>
<td valign="top">Test the area of flash 0x0FFC-0x100C</td>
</tr>
<tr>
<td valign="top">ram0<br>
</td>
<td valign="top">Repeatedly access 0x0000 - 0x0020<br>
</td>
</tr>
<tr>
<td valign="top">ram1<br>
</td>
<td valign="top">Repeatedly access 0xF007 - 0xF017<br>
</td>
</tr>
<tr>
<td valign="top">alu<br>
</td>
<td valign="top">Perform combinations of mul, fmul, inc and
dec<br>
</td>
</tr>
<tr>
<td valign="top">nop<br>
</td>
<td valign="top">Lots of nops<br>
</td>
</tr>
<tr>
<td valign="top">branch<br>
</td>
<td valign="top">Repeatedly branch randomly in low flash<br>
</td>
</tr>
</tbody>
</table>
<br>
Each test was run 8 times, and outliers excluded. All were run in
the same harness, with the same crystal, resistors, etc.<br>
<br>
Results across each test. These show the distributions of the
measurements taken, where the distribution consists of the 28
chips.<br>
<img src="cid:part1.08080105.04000409@dynamicdevices.co.uk" alt=""><br>
<br>
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.<br>
<br>
For each chip:<br>
<img src="cid:part2.05040307.09010701@dynamicdevices.co.uk" alt=""><br>
Mean power for each chip:<br>
<img src="cid:part3.09070202.00070302@dynamicdevices.co.uk" alt=""><br>
<br>
<br>
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).<br>
<br>
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.<br>
<img src="cid:part4.07040301.07000409@dynamicdevices.co.uk" alt=""><br>
Legend for the above graph:<br>
<table cellpadding="2" cellspacing="2" width="318" border="1"
height="58">
<tbody>
<tr>
<td valign="top">Blue cross<br>
</td>
<td valign="top">ram1<br>
</td>
</tr>
<tr>
<td valign="top">Red star<br>
</td>
<td valign="top">ram0<br>
</td>
</tr>
<tr>
<td valign="top">Green plus<br>
</td>
<td valign="top">alu<br>
</td>
</tr>
<tr>
<td valign="top">Black plus<br>
</td>
<td valign="top">flash3<br>
</td>
</tr>
<tr>
<td valign="top">Green cross<br>
</td>
<td valign="top">flash2<br>
</td>
</tr>
<tr>
<td valign="top">Blue star<br>
</td>
<td valign="top">flash1<br>
</td>
</tr>
<tr>
<td valign="top">Red plus<br>
</td>
<td valign="top">flash0<br>
</td>
</tr>
<tr>
<td valign="top">Black star<br>
</td>
<td valign="top">nop<br>
</td>
</tr>
</tbody>
</table>
<br>
<br>
Any thoughts / ideas for more tests are welcome.<br>
<br>
<br>
James<br>
<br>
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<br>
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