[MAGEEC] Chip variations: tests, results, and graphs
James Pallister
James.Pallister at bristol.ac.uk
Sun Jul 27 17:27:58 BST 2014
No JTAG - the chips are flashed with a bootloader, which is only active
on chip reset. Everything is programmed via a USB-to-serial thingy.
On 27/07/14 17:25, Steve Kerrison wrote:
>
> Is JTAG connected during test runs? Interested to know how much
> difference that makes, although it should be constant thus irrelevant.
>
> On 27 Jul 2014 17:13, "James Pallister" <James.Pallister at bristol.ac.uk
> <mailto:James.Pallister at bristol.ac.uk>> 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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