add tui and persistent targets

include/settings_store.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <Arduino.h>
+#include <EEPROM.h>
+
+#include "config.h"
+
+// After TuningData (15 bytes) + checksum (1 byte) at address 0
+static const uint16_t SETTINGS_MAGIC = 0xDA7E;
+static const int SETTINGS_EEPROM_ADDR = 16;
+
+struct SettingsData {
+  uint16_t magic = 0;
+  float targetC = TARGET_TEMP_C;
+};
+
+inline uint8_t settingsChecksum(const SettingsData &data) {
+  const uint8_t *bytes = reinterpret_cast<const uint8_t *>(&data);
+  uint8_t sum = 0;
+  for (uint8_t i = 0; i < sizeof(SettingsData) - 1; ++i) {
+    sum ^= bytes[i];
+  }
+  return sum;
+}
+
+inline bool settingsLoad(SettingsData &out) {
+  EEPROM.get(SETTINGS_EEPROM_ADDR, out);
+  const uint8_t stored = EEPROM.read(SETTINGS_EEPROM_ADDR + sizeof(SettingsData));
+  if (out.magic != SETTINGS_MAGIC) {
+    return false;
+  }
+  return settingsChecksum(out) == stored;
+}
+
+inline void settingsSave(const SettingsData &data) {
+  EEPROM.put(SETTINGS_EEPROM_ADDR, data);
+  EEPROM.write(SETTINGS_EEPROM_ADDR + sizeof(SettingsData), settingsChecksum(data));
+}
+
+inline void settingsSaveTarget(float targetC) {
+  SettingsData data;
+  data.magic = SETTINGS_MAGIC;
+  data.targetC = targetC;
+  settingsSave(data);
+}
+
+inline void settingsClear() {
+  SettingsData cleared;
+  settingsSave(cleared);
+}