optional RTC 3231 integration

src/rtc_ds3231.cpp

@@ -0,0 +1,105 @@
+#include "rtc_ds3231.h"
+#include "config.h"
+#include <Wire.h>
+#include <time.h>
+
+static constexpr uint8_t DS3231_ADDR = 0x68;
+
+static uint8_t bcd_to_dec(uint8_t val) {
+  return static_cast<uint8_t>((val >> 4) * 10 + (val & 0x0F));
+}
+
+static uint8_t dec_to_bcd(uint8_t val) {
+  return static_cast<uint8_t>(((val / 10) << 4) | (val % 10));
+}
+
+static bool read_registers(uint8_t start_reg, uint8_t *out, size_t len) {
+  if (!out || len == 0) {
+    return false;
+  }
+  Wire.beginTransmission(DS3231_ADDR);
+  Wire.write(start_reg);
+  if (Wire.endTransmission(false) != 0) {
+    return false;
+  }
+  size_t read = Wire.requestFrom(DS3231_ADDR, static_cast<uint8_t>(len));
+  if (read != len) {
+    return false;
+  }
+  for (size_t i = 0; i < len; ++i) {
+    out[i] = Wire.read();
+  }
+  return true;
+}
+
+static bool write_registers(uint8_t start_reg, const uint8_t *data, size_t len) {
+  if (!data || len == 0) {
+    return false;
+  }
+  Wire.beginTransmission(DS3231_ADDR);
+  Wire.write(start_reg);
+  for (size_t i = 0; i < len; ++i) {
+    Wire.write(data[i]);
+  }
+  return Wire.endTransmission() == 0;
+}
+
+bool rtc_ds3231_init() {
+  Wire.begin(PIN_OLED_SDA, PIN_OLED_SCL);
+  Wire.setClock(100000);
+  return rtc_ds3231_is_present();
+}
+
+bool rtc_ds3231_is_present() {
+  Wire.beginTransmission(DS3231_ADDR);
+  return Wire.endTransmission() == 0;
+}
+
+bool rtc_ds3231_read_epoch(uint32_t &epoch_utc) {
+  uint8_t regs[7] = {};
+  if (!read_registers(0x00, regs, sizeof(regs))) {
+    return false;
+  }
+
+  uint8_t sec = bcd_to_dec(regs[0] & 0x7F);
+  uint8_t min = bcd_to_dec(regs[1] & 0x7F);
+  uint8_t hour = bcd_to_dec(regs[2] & 0x3F);
+  uint8_t day = bcd_to_dec(regs[4] & 0x3F);
+  uint8_t month = bcd_to_dec(regs[5] & 0x1F);
+  uint16_t year = 2000 + bcd_to_dec(regs[6]);
+
+  struct tm tm_utc = {};
+  tm_utc.tm_sec = sec;
+  tm_utc.tm_min = min;
+  tm_utc.tm_hour = hour;
+  tm_utc.tm_mday = day;
+  tm_utc.tm_mon = month - 1;
+  tm_utc.tm_year = year - 1900;
+  tm_utc.tm_isdst = 0;
+
+  time_t t = timegm(&tm_utc);
+  if (t <= 0) {
+    return false;
+  }
+  epoch_utc = static_cast<uint32_t>(t);
+  return true;
+}
+
+bool rtc_ds3231_set_epoch(uint32_t epoch_utc) {
+  time_t t = static_cast<time_t>(epoch_utc);
+  struct tm tm_utc = {};
+  if (!gmtime_r(&t, &tm_utc)) {
+    return false;
+  }
+
+  uint8_t regs[7] = {};
+  regs[0] = dec_to_bcd(static_cast<uint8_t>(tm_utc.tm_sec));
+  regs[1] = dec_to_bcd(static_cast<uint8_t>(tm_utc.tm_min));
+  regs[2] = dec_to_bcd(static_cast<uint8_t>(tm_utc.tm_hour));
+  regs[3] = dec_to_bcd(static_cast<uint8_t>(tm_utc.tm_wday + 1));
+  regs[4] = dec_to_bcd(static_cast<uint8_t>(tm_utc.tm_mday));
+  regs[5] = dec_to_bcd(static_cast<uint8_t>(tm_utc.tm_mon + 1));
+  regs[6] = dec_to_bcd(static_cast<uint8_t>((tm_utc.tm_year + 1900) - 2000));
+
+  return write_registers(0x00, regs, sizeof(regs));
+}