[MAGEEC] Chip variations: tests, results, and graphs

[James Pallister]

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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