This is a part of a bigger work that compares energy cost of different ways of communications
between SMU and DUT: GPIO, USART etc.
-Qoitech Otii Arc as SMU;
-Atmel ATmega328PB Xplained Mini as DUT;
-AtmelICE as ISP programmer.
-Otii PC SW to control SMU and display recordings;
-custom program for 328.
328 wakes up every 1 s on timer interrupt. On each wakeup it sends a string to SMU. String length
varies in cycles from 2 to 11.
Looking at the recordings of current drain I've noticed several things that I can not explain
at the moment:
1. The longer is the string, the higher is maximal current. See impulses on the upper pane and
their corresponding UART messages below. Maximal current for a pulse grows for string lengths from
two through six and stops at 12.8 mA for seven chars and longer strings (up to 11, did not test
it for longer strings).
Looks like short strings are sent before power system starts up completely? Then it appears that
we start sending too early?
2. Maximal current is lower for faster UART speeds. For 38400 (red line) it's 1.5 mA less
than for 9600 (green line) on a six-char string.
This I don't understand. Either something obvious or I'm measuring/interpreting it wrong.
Has anyone seen the same? Can confirm? Explain?
Source code, hi-res images and recordings made by SMU can be found in attachment.