Self-learning holdover temperature compensation

mk4-date/Core/Src/main.c

@@ -488,7 +488,13 @@ static inline void latchDisplay(void){
   buffer_a[3] = pre_buffer_a[3];
   buffer_a[4] = pre_buffer_a[4];
 
+  // dp_pos is the 1-based digit the decimal point attaches to (0 = none). It comes from
+  // text_idx, which the sender can advance past the 10-digit display, and it indexes the
+  // 5-entry buffer_a/buffer_b below. Clamp to each orientation's valid range so a stray or
+  // garbled '.' in the UART stream can't drive a negative / out-of-range index into RAM.
   if (!dp_pos) return;
+  if (inverted) { if (dp_pos > 9) return; }   // inverted: 9-dp_pos goes negative at 10
+  else          { if (dp_pos > 10) return; }  // non-inverted: dp_pos-6 tops out at [4]
 
   if (inverted){
     if (dp_pos>=5) {
@@ -601,7 +607,7 @@ static inline void parseByte(uint8_t x){
       dp_pos = text_idx;
       return;
     }
-    if(text_idx > MAX_TEXT_LEN) return;
+    if(text_idx >= MAX_TEXT_LEN) return;  // was '>': at text_idx==MAX_TEXT_LEN this wrote text[32], 1 byte past the buffer
 
     if (text_idx < 10) setDigitPre(text_idx, x);
     text[text_idx++] = x;

mk4-time/Core/Inc/astro.h

@@ -0,0 +1,55 @@
+/*
+ * astro.h — minimal solar/lunar/grid astronomy for the Precision Clock Mk IV.
+ *
+ * Self-contained C99 + <math.h>; NO firmware dependencies, so it compiles and
+ * unit-tests natively (see test_astro.c). All angles in degrees at the API
+ * boundary; UTC instants are passed as a double of Unix seconds.
+ *
+ * Algorithms are low-precision (NOAA/Meeus-class) approximations — accurate to a
+ * fraction of a degree / a minute or two, which is all a 7-segment readout shows,
+ * and cheap enough to evaluate once per mode entry on the STM32's soft-double.
+ */
+#ifndef ASTRO_H
+#define ASTRO_H
+
+/* (a) Sun apparent alt/az for an observer at (lat, lon) decimal degrees, N+/E+,
+ *     at the given UTC instant. Writes azimuth in [0,360) measured from North
+ *     clockwise, and elevation in [-90,90] (negative = below the horizon).
+ *     No refraction or parallax correction. */
+void   sun_az_el(double lat, double lon, double unix_s, double *az, double *el);
+
+/* (b) Sun event times for the UTC calendar day containing unix_s.
+ *     Every output is a decimal UTC hour and MAY be < 0 or > 24 (the event falls
+ *     on the previous/next day) — callers add the local offset and wrap, they do
+ *     NOT clamp. solar_noon is always written. Returns 0 normally; returns
+ *     nonzero on polar day/night (sun never crosses -0.833 deg), in which case
+ *     sunrise/sunset are left untouched and only solar_noon is meaningful.
+ *     Any of the optional twilight pointers may be NULL. */
+int    sun_times(double lat, double lon, double unix_s,
+                 double *sunrise, double *sunset, double *solar_noon,
+                 double *civil_dusk, double *nautical_dusk, double *golden_dusk);
+
+/* (c) Moon. phase is the synodic fraction [0,1): 0=new, .25=first quarter,
+ *     .5=full, .75=last quarter. */
+double moon_phase(double unix_s);
+double moon_illuminated_fraction(double phase);   /* (1 - cos(2*pi*phase)) / 2  */
+int    moon_phase_index(double phase);            /* 0..7, see ASTRO_MOON_NAMES  */
+
+/* (d) Equation of time in minutes (+ = apparent sun ahead of mean/clock sun). */
+double equation_of_time(double unix_s);
+
+double local_sidereal_time(double unix_s, double lon); /* LMST, hours [0,24), lon E+ */
+double local_solar_time(double unix_s, double lon);    /* apparent solar, hours [0,24) */
+
+/* (d2) Subsolar point at the given UTC instant: latitude = solar declination,
+ *      longitude in [-180,180] (E+). Time-only — needs no observer position. */
+void   sun_subsolar(double unix_s, double *lat, double *lon);
+
+/* (e) 6-character Maidenhead locator for (lat, lon). out must hold >= 7 bytes.
+ *     Writes "----\0" if either coordinate is non-finite. */
+void   maidenhead(double lat, double lon, char out[7]);
+
+/* Phase-index -> short name. Index from moon_phase_index(). */
+extern const char *const ASTRO_MOON_NAMES[8];
+
+#endif /* ASTRO_H */