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

[James Pallister]

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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