Mr. Integral
Embedded notes/Building Reliable Systems/Power and Reliability

UNIT 14 · BUILDING RELIABLE SYSTEMS

Power and Reliability

Run for years on a battery, and recover when things go wrong.

6 lessons23 guided experiments65 min full read

A device on a bench is plugged in, watched, and reset by hand when it hangs. A device in the field runs from a battery for years, loses power in the middle of a write, meets a supply that sags when a motor starts, and has nobody to press its reset button. This unit is about the second kind: spending as little charge as possible, noticing when something has gone wrong, and coming back in a known state.

Start with lesson 1 →
∫ MR-INTEGRAL · 15 UNITS · 90 LESSONS016 lessonsPinssignals and circuits036 lessonsCPU coreand memory026 lessonsRegisters096 lessonsInterruptcontroller136 lessonsSchedulertasks and deadlines046 lessonsFlash imagebuilt by the toolchain156 lessonsSecure bootupdates and keys056 lessonsBoot ROMand reset066 lessonsDebug portprobe, trace146 lessonsPowersleep, brown-out126 lessonsDMA076 lessonsGPIOpins in and out086 lessonsClocksand timers106 lessonsUART · SPI · I²Cserial links116 lessonsADC · DACanalog
∫ MR-INTEGRAL · 15 UNITS01Pins · signals and circuits036 lessonsCPU coreand memory026 lessonsRegistersC close to the metal096 lessonsInterruptcontroller136 lessonsSchedulertasks and deadlines046 lessonsFlash imagebuilt by the toolchain156 lessonsSecure bootupdates and keys056 lessonsBoot ROMand reset066 lessonsDebug portprobe, trace146 lessonsPowersleep, brown-out126 lessonsDMA076 lessonsGPIOpins in and out086 lessonsClocksand timers106 lessonsUART · SPI · I²Cserial links116 lessonsADC · DACanalog

The unit in six ideas

  1. 1An idle loop pays full dynamic power; sleeping means stopping clocks, lowering voltage or switching domains off.
  2. 2A battery’s mAh rating is charge (1 mAh = 3.6 C); life is capacity divided by the average current.
  3. 3A watchdog resets the chip unless firmware refreshes it in time; the RP2040’s can pause while a debugger halts the core, and the STM32 IWDG runs from its own RC clock and cannot be stopped.
  4. 4Below its specified voltage a chip is unreliable; a brown-out reset must fire before the supply gets there, and an early-warning detector buys time to prepare.
  5. 5Erase-then-program leaves a window with no valid data; never overwrite the only copy.
  6. 6Test logic on the host in milliseconds, drivers and timing on the target, and the whole device in a hardware-in-the-loop rig.

Lessons

  1. LESSON 01 · 4 EXPERIMENTS · 12 MIN

    Sleep States and Wake-Up Sources

    What does it take to make a microcontroller actually sleep, and what wakes it again?

  2. LESSON 02 · 4 EXPERIMENTS · 10 MIN

    Measuring Power and Energy

    Is the meter wrong, is the datasheet wrong, or is something on the board awake that nobody asked to be?

  3. LESSON 03 · 4 EXPERIMENTS · 11 MIN

    Watchdogs and Recovery Strategies

    What should it watch, and what should happen after it bites?

  4. LESSON 04 · 4 EXPERIMENTS · 12 MIN

    Brownouts, Reset Causes, and Safe States

    What does a chip do while its voltage sags, how does firmware find out afterwards, and how do you keep the hardware safe in the meantime?

  5. LESSON 05 · 4 EXPERIMENTS · 10 MIN

    Persistent Settings and Power-Loss Safety

    How do you store settings so that a power cut at any instant leaves one complete, correct copy?

  6. LESSON 06 · 3 EXPERIMENTS · 10 MIN

    Testing Firmware and Handling Failures

    How do you test the code that only runs when something has gone wrong, and how should firmware behave when a failure happens for real?