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Brian Pugh 70faa29dac perf: light-sleep idle + refresh downclock — ~3.2x active reading time (X3-measured) (#2525)
## Summary

Reduces active-reading power draw ~3.2x, measured end-to-end on an X3
with a [Nordic
PPK2](https://www.nordicsemi.com/Products/Development-hardware/Power-Profiler-Kit-2)
at the battery terminals (slim build, USB cable removed, 3.8v). Three
independent changes:

1. **Light-sleep between input polls when idle** (the big one): after 1
s of inactivity the main loop replaces its busy `delay(50)` with 50 ms
timer-paced `esp_light_sleep_start()` slices. Poll cadence and input
latency are unchanged — the CPU sleeps between polls instead of spinning
at 10 MHz. Guards: never sleeps while a `HalPowerManager::Lock` is held
(render in flight), WiFi is up, or USB is connected (light sleep kills
the CDC link).
2. **Two-stage idle backoff**: downclock at 500 ms, light sleep at 1 s,
replacing the flat 3 s full-speed window. Renders re-raise the clock via
`Lock` the moment they start, so the full-speed tail only ever served
loop bookkeeping. (The 3 s value in #852 was a placeholder;
responsiveness verified on device against stock.)
3. **Refresh BUSY-wait downclock**: drops the CPU to 10 MHz while
`pollBusy()` polls the BUSY pin (0.3–2 s per refresh), via new optional
hooks in the SDK — **depends on Free-Ink/freeink-sdk/pull/8**. Plus a 1
Hz throttle on the X3's I2C-based USB detection (was polled every loop).

(1+2) reduced average static-page-current from 9.68mA to 3.45mA.
Reducing the battery-monitor polling frequency further reduced it to
2.78mA.

Before merging, we'll need to update the submodule reference.

## Measured results (PPK2, X3)

| Metric | Before | After |
|---|---|---|
| Idle on a static page | 9.68 mA | **2.78 mA** |
| Fast page turn (incl. post-turn behavior) | ~100 mC | **28.98 mC** |
| Post-turn 160 MHz tail | 21.2 mA x 3 s | eliminated |
| Session average @ 30 s/page | ~11.6 mA | **~3.6 mA (~3.2x reading
time)** |
| Deep sleep | 12.8 µA | unchanged |

## Typical-day profiles

Assuming someone spends 30s per page.

- **Light**: 1 h reading, 10 lock/wake cycles, remaining ~23 h deep
sleep
- **Heavy**: 2 h reading, 20 lock/wake cycles, remaining ~22 h deep
sleep
- Per-day cost components: reading 11.6 → 3.6 mA (session avg),
lock+wake cycle
0.113 → 0.099 mAh each (sleep-screen mode), deep sleep 12.8 µA
(unchanged,
  ~0.29 mAh/day)
- Excluded: WiFi sessions, cold chapter indexing, self-discharge

### Days per charge (650mAh)

| Profile | Before | After | Ratio |
|---|---|---|---|
| Light (1 h/day, 10 locks) | 13.0 mAh/day → ~50 days | 4.9 mAh/day →
~133 days | 2.7× |
| Heavy (2 h/day, 20 locks) | 25.7 mAh/day → ~25 days | 9.5 mAh/day →
~68 days | 2.7× |
| Pure active reading | 11.6 mA → ~56 h | 3.6 mA → ~180 h | 3.2× |

### Caveats

- "After" saturates in reality: Li-ion self-discharge (~2–3%/month) is
not modeled
  and becomes the limiter once firmware draw is this low.
- Faster page-turners trend toward ~2.8×, slower readers slightly above
3.2×.
- Frequent locking dilutes the ratio (wake = full cold boot, barely
touched by the
power branch): at 10–20 locks/day, cycles are ~20% of the "after"
budget.
---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**YES**_

---------
2026-08-12 20:57:45 -04:00

153 lines
5.8 KiB
C++

#include <HalDisplay.h>
#include <HalGPIO.h>
// Global HalDisplay instance
HalDisplay display;
#define SD_SPI_MISO 7
HalDisplay::HalDisplay() : einkDisplay(EPD_SCLK, EPD_MOSI, EPD_CS, EPD_DC, EPD_RST, EPD_BUSY) {}
HalDisplay::~HalDisplay() {}
void HalDisplay::begin(bool seamless) {
// Set X3-specific panel mode before initializing.
if (gpio.deviceIsX3()) {
einkDisplay.setDisplayX3();
}
einkDisplay.begin();
if (seamless) {
// Defuse the SDK's X3 _x3InitialFullSyncsRemaining counter (no-op on X4)
// so the first paint isn't promoted to FULL (~770ms). Skips the wakeup-
// gated requestResync() below for the same reason.
einkDisplay.skipInitialResync();
return;
}
// Request resync after specific wakeup events to ensure clean display state.
const auto wakeupReason = gpio.getWakeupReason();
if (wakeupReason == HalGPIO::WakeupReason::PowerButton || wakeupReason == HalGPIO::WakeupReason::AfterFlash ||
wakeupReason == HalGPIO::WakeupReason::Other) {
einkDisplay.requestResync();
}
}
void HalDisplay::clearScreen(uint8_t color) const { einkDisplay.clearScreen(color); }
void HalDisplay::drawImage(const uint8_t* imageData, uint16_t x, uint16_t y, uint16_t w, uint16_t h,
bool fromProgmem) const {
einkDisplay.drawImage(imageData, x, y, w, h, fromProgmem);
}
void HalDisplay::drawImageTransparent(const uint8_t* imageData, uint16_t x, uint16_t y, uint16_t w, uint16_t h,
bool fromProgmem) const {
einkDisplay.drawImageTransparent(imageData, x, y, w, h, fromProgmem);
}
EInkDisplay::RefreshMode convertRefreshMode(HalDisplay::RefreshMode mode) {
switch (mode) {
case HalDisplay::FULL_REFRESH:
return EInkDisplay::FULL_REFRESH;
case HalDisplay::HALF_REFRESH:
return EInkDisplay::HALF_REFRESH;
case HalDisplay::FAST_REFRESH:
default:
return EInkDisplay::FAST_REFRESH;
}
}
void HalDisplay::displayBuffer(HalDisplay::RefreshMode mode, bool turnOffScreen) {
if (gpio.deviceIsX3() && mode == RefreshMode::HALF_REFRESH) {
einkDisplay.requestResync(1);
}
einkDisplay.displayBuffer(convertRefreshMode(mode), turnOffScreen);
}
void HalDisplay::displayBufferAsync(HalDisplay::RefreshMode mode) {
if (gpio.deviceIsX3() && mode == RefreshMode::HALF_REFRESH) {
einkDisplay.requestResync(1);
}
einkDisplay.displayBufferAsyncNoShadow(convertRefreshMode(mode));
}
void HalDisplay::waitRefreshComplete() { einkDisplay.waitRefreshComplete(); }
bool HalDisplay::supportsAsyncRefresh() const { return einkDisplay.supportsAsyncRefresh(); }
void HalDisplay::refreshDisplay(HalDisplay::RefreshMode mode, bool turnOffScreen) {
if (gpio.deviceIsX3() && mode == RefreshMode::HALF_REFRESH) {
einkDisplay.requestResync(1);
}
einkDisplay.refreshDisplay(convertRefreshMode(mode), turnOffScreen);
}
void HalDisplay::setInverted(bool inverted) { einkDisplay.setInverted(inverted); }
bool HalDisplay::toggleInverted() { return einkDisplay.toggleInverted(); }
bool HalDisplay::isInverted() const { return einkDisplay.isInverted(); }
void HalDisplay::deepSleep() { einkDisplay.deepSleep(); }
void HalDisplay::setBusyWaitSliceHook(bool (*sliceHook)(int8_t busyPin, uint8_t busyLevel)) {
einkDisplay.setBusyWaitSliceHook(sliceHook);
}
uint8_t* HalDisplay::getFrameBuffer() const { return einkDisplay.getFrameBuffer(); }
uint8_t* HalDisplay::lendFrameBufferStorage(uint32_t* sizeOut) { return einkDisplay.lendBuildStorage(sizeOut); }
void HalDisplay::returnFrameBufferStorage() { einkDisplay.returnBuildStorage(); }
void HalDisplay::copyGrayscaleBuffers(const uint8_t* lsbBuffer, const uint8_t* msbBuffer) {
einkDisplay.copyGrayscaleBuffers(lsbBuffer, msbBuffer);
}
void HalDisplay::displayGrayscaleBase(RefreshMode fallback, bool turnOffScreen) {
// X3: a HALF fallback means the caller wants a clean base (e.g. the sleep
// cover, a full-screen swap from arbitrary prior content). Without this, the
// X3 grayscale base takes its gentle differential happy path and the prior
// home/reader frame ghosts through the soft aa_pre_bw_mid waveform. Forcing a
// resync makes displayGrayscaleBase clear first, matching displayBuffer(HALF).
// The reader's FAST path is deliberately left on the differential path so
// per-page grayscale stays cheap.
if (gpio.deviceIsX3() && fallback == RefreshMode::HALF_REFRESH) {
einkDisplay.requestResync(1);
}
einkDisplay.displayGrayscaleBase(convertRefreshMode(fallback), turnOffScreen);
}
void HalDisplay::preconditionGrayscale() { einkDisplay.preconditionGrayscale(); }
void HalDisplay::preconditionGrayscale(uint16_t x, uint16_t y, uint16_t w, uint16_t h) {
einkDisplay.preconditionGrayscale(x, y, w, h);
}
void HalDisplay::copyGrayscaleLsbBuffers(const uint8_t* lsbBuffer) { einkDisplay.copyGrayscaleLsbBuffers(lsbBuffer); }
void HalDisplay::copyGrayscaleMsbBuffers(const uint8_t* msbBuffer) { einkDisplay.copyGrayscaleMsbBuffers(msbBuffer); }
void HalDisplay::cleanupGrayscaleBuffers(const uint8_t* bwBuffer) { einkDisplay.cleanupGrayscaleBuffers(bwBuffer); }
void HalDisplay::displayGrayBuffer(bool turnOffScreen) { einkDisplay.displayGrayBuffer(turnOffScreen); }
void HalDisplay::writeGrayscalePlaneStrip(bool lsbPlane, const uint8_t* rows, uint16_t yStart, uint16_t numRows) {
einkDisplay.writeGrayscalePlaneStrip(lsbPlane ? EInkDisplay::GRAY_PLANE_LSB : EInkDisplay::GRAY_PLANE_MSB, rows,
yStart, numRows);
}
bool HalDisplay::supportsStripGrayscale() const { return einkDisplay.supportsStripGrayscale(); }
uint16_t HalDisplay::getDisplayWidth() const { return einkDisplay.getDisplayWidth(); }
uint16_t HalDisplay::getDisplayHeight() const { return einkDisplay.getDisplayHeight(); }
uint16_t HalDisplay::getDisplayWidthBytes() const { return einkDisplay.getDisplayWidthBytes(); }
uint32_t HalDisplay::getBufferSize() const { return einkDisplay.getBufferSize(); }