feat: lower CPU freq on idle, add HalPowerManager (#852)

## Summary Continue my experiment from https://github.com/crosspoint-reader/crosspoint-reader/pull/801 This PR add the ability to lower the CPU frequency on extended idle period (currently set to 3 seconds). By default, the esp32c3 CPU is set to 160MHz, and now on idle, we can reduce it to just 10MHz. Note that while this functionality is already provided by [esp power management](https://docs.espressif.com/projects/esp-idf/en/v4.3/esp32c3/api-reference/system/power_management.html), the current Arduino build lacks of this, and enabling it is just too complicated (not worth the effort compared to this PR) Update: more info in https://github.com/crosspoint-reader/crosspoint-reader/pull/852#issuecomment-3904562827 ## Testing Pre-condition for each test case: the battery is charged to 100%, and is left plugged in after fully charged for an extra 1 hour. The table below shows how much battery is **used** for a given duration: | case / duration | 6 hrs | 12 hrs | | --- | --- | --- | | `delay(10)` | 26% | 48% | | `delay(50)`, PR https://github.com/crosspoint-reader/crosspoint-reader/pull/801 | 20% | Not tested | | `delay(50)` + low CPU freq (This PR) | Not tested | 25% | | `delay(10)` + low CPU freq (1) | Not tested | Not tested | (1) I decided not to test this case because it may not make sense. The problem is that CPU frequency vs power consumption do not follow a linear relationship, see [this](https://www.arrow.com/en/research-and-events/articles/esp32-power-consumption-can-be-reduced-with-sleep-modes) as an example. So, tight loop (10ms) + lower CPU freq significantly impact battery life, because the active CPU time is now much higher compared to the wall time. **So in conclusion, this PR improves ~150% to ~200% battery use time per charge.** The projected battery life is now: ~36-48 hrs of reading time (normal reading, no wifi) --- ### 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? **NO**
2026-02-18 15:12:29 +01:00
parent 9125a7ce68
commit 6ec5fc5603
9 changed files with 170 additions and 32 deletions
--- a/lib/hal/HalPowerManager.cpp
+++ b/lib/hal/HalPowerManager.cpp
@@ -0,0 +1,95 @@
+#include "HalPowerManager.h"
+
+#include <Logging.h>
+#include <WiFi.h>
+#include <esp_sleep.h>
+
+#include <cassert>
+
+#include "HalGPIO.h"
+
+HalPowerManager powerManager;  // Singleton instance
+
+void HalPowerManager::begin() {
+  pinMode(BAT_GPIO0, INPUT);
+  normalFreq = getCpuFrequencyMhz();
+  modeMutex = xSemaphoreCreateMutex();
+  assert(modeMutex != nullptr);
+}
+
+void HalPowerManager::setPowerSaving(bool enabled) {
+  if (normalFreq <= 0) {
+    return;  // invalid state
+  }
+
+  auto wifiMode = WiFi.getMode();
+  if (wifiMode != WIFI_MODE_NULL) {
+    // Wifi is active, force disabling power saving
+    enabled = false;
+  }
+
+  // Note: We don't use mutex here to avoid too much overhead,
+  // it's not very important if we read a slightly stale value for currentLockMode
+  const LockMode mode = currentLockMode;
+
+  if (mode == None && enabled && !isLowPower) {
+    LOG_DBG("PWR", "Going to low-power mode");
+    if (!setCpuFrequencyMhz(LOW_POWER_FREQ)) {
+      LOG_DBG("PWR", "Failed to set CPU frequency = %d MHz", LOW_POWER_FREQ);
+      return;
+    }
+    isLowPower = true;
+
+  } else if ((!enabled || mode != None) && isLowPower) {
+    LOG_DBG("PWR", "Restoring normal CPU frequency");
+    if (!setCpuFrequencyMhz(normalFreq)) {
+      LOG_DBG("PWR", "Failed to set CPU frequency = %d MHz", normalFreq);
+      return;
+    }
+    isLowPower = false;
+  }
+
+  // Otherwise, no change needed
+}
+
+void HalPowerManager::startDeepSleep(HalGPIO& gpio) const {
+  // Ensure that the power button has been released to avoid immediately turning back on if you're holding it
+  while (gpio.isPressed(HalGPIO::BTN_POWER)) {
+    delay(50);
+    gpio.update();
+  }
+  // Arm the wakeup trigger *after* the button is released
+  esp_deep_sleep_enable_gpio_wakeup(1ULL << InputManager::POWER_BUTTON_PIN, ESP_GPIO_WAKEUP_GPIO_LOW);
+  // Enter Deep Sleep
+  esp_deep_sleep_start();
+}
+
+int HalPowerManager::getBatteryPercentage() const {
+  static const BatteryMonitor battery = BatteryMonitor(BAT_GPIO0);
+  return battery.readPercentage();
+}
+
+HalPowerManager::Lock::Lock() {
+  xSemaphoreTake(powerManager.modeMutex, portMAX_DELAY);
+  // Current limitation: only one lock at a time
+  if (powerManager.currentLockMode != None) {
+    LOG_ERR("PWR", "Lock already held, ignore");
+    valid = false;
+  } else {
+    powerManager.currentLockMode = NormalSpeed;
+    valid = true;
+  }
+  xSemaphoreGive(powerManager.modeMutex);
+  if (valid) {
+    // Immediately restore normal CPU frequency if currently in low-power mode
+    powerManager.setPowerSaving(false);
+  }
+}
+
+HalPowerManager::Lock::~Lock() {
+  xSemaphoreTake(powerManager.modeMutex, portMAX_DELAY);
+  if (valid) {
+    powerManager.currentLockMode = None;
+  }
+  xSemaphoreGive(powerManager.modeMutex);
+}