1. Power and energy

ATtiny85_Datasheet.pdf

  • Go to section 7 in the datasheet.

1.1. ATtiny sleep modes

  • Find the MCUCR register information.

    • How many sleep modes are there? What do they mean?

What entities are affected by these configuration bits?

  • There are only 3 rows in Table 7-1 but there are 2 SM[1:0] bits. → Where is the fourth row?



In the ShortSquawker, with everything being triggered by a Timer0 interrupt, there is a time interval after the Timer0 ISR finishes where the CPU has nothing to do.

  • What code is the CPU executing during that time in the original Arduino (and your pure C) version?



  • What sleep mode is most appropriate to enter into during that time interval? (and why, exactly)



1.2. Brown-out detector

A comparator circuit that triggers a system RESET when the power supply drops below a certian voltage.

Read the first paragraph of Section 7.2

The details of exactly when the BOD is operating/enabled are important for minimizing the power supply current.

1.3. Power Reduction Register

Section 7.3

Seems useful to know if you want to …​ reduce power.

  • Peripheral current state is frozen

    • …​ waking up …​ puts the module in the same state as before shutdown.

2. ATtiny85 strategy

Given the datasheet’s descriptions and knowledge of how ShortSquawker works:

Map out a strategy for reducing power usage (supply current) during all of the operation modes.

It is useful to have a "timing diagram" of the code’s execution.

Start with the hints in Section 7.4, then add more ideas given the application’s code.

  • When do you need to re-initialize registers? Does any sleep or power mode wipe out your configuration?

  • What supply current do you expect to measure in each of the modes and time intervals of operating the ShortSquawker?

    • Having a prediction is the first step to lowering the current draw, matching against actual measurements.