[dstampe]

The big spike followed by high consumption and noise is what I would expect from the eInk circuitry. This probably has a high-voltage DC-to-DC converter, followed by a matrix of drivers for row and column lines in the display.

This shows a big spike of current draw as it starts up and charges all its capacitors. Then the variable load producing the noise is a combination of this supply and the variable capacitive load as different lines in the eInk display are charged and discharged, Obviously this is a big user of power.

There seem to be 3 load levels. One is fairly low, probably the CPU coming out of sleep mode. The second appears to correspond to display preparation, as it's much longer for the PDF file display. Not sure if this is CPU use, display buffer being powered up, or flash memory access. The highest level seems to be when the eInk power supply is being used.

When used with external flash, the second level of current draw takes longer before the page display, so this second level probably does indicate internal or external flash memory access. (External flash access also appears to be much slower). Also, the CPU stays active for several seconds longer after a page update. So using external flash memory will shorten battery life by up to 40%, I would expect. Of cource, it looks like viewing complex PDF files is even more expensive.