UA1ZBE Custom Firmware v1.0

Features:
- VFO mode with direct frequency input
- POCSAG decoder (512/1200 baud) with BCH(31,21) correction
- Full-screen Spectrum analyzer
- FM Radio receiver
- RSSI signal indicator overlay
- Custom boot splash (UA1ZBE / POCSAG pager / build date)

Architecture:
- app/mode.c — mode dispatcher (VFO/POCSAG/Spectrum/FM)
- app/boot_splash.c — 2-second boot splash
- app/pocsag/ — POCSAG decoder + BCH correction
- app/display_rssi.c — RSSI indicator
- main.c — entry point with custom init
- syscalls.c — bare-metal _sbrk stub

Build: arm-none-eabi-gcc -Os -flto -Wall -Werror -Wextra
Size: 57.9KB Flash / 3.6KB RAM

Controls:
- 0-9: Direct frequency input (VFO)
- SK2: POCSAG mode
- SK1: Spectrum analyzer
- 0: FM Radio
- EXIT: Return to VFO
- F/*: Toggle 512/1200 baud (in POCSAG)

app/mode.h

@@ -0,0 +1,50 @@
+/* UA1ZBE Custom Firmware - Mode Dispatcher
+ *
+ * Manages switching between operating modes:
+ *   MODE_VFO       — Main VFO mode (default)
+ *   MODE_POCSAG    — POCSAG decoder
+ *   MODE_SPECTRUM  — Spectrum analyzer
+ *   MODE_FM        — FM radio receiver
+ *
+ * Key mappings:
+ *   KEY_SIDE2 (SK2) → POCSAG mode
+ *   KEY_SIDE1 (SK1) → Spectrum mode
+ *   KEY_EXIT        → Return to VFO
+ *   KEY_0 (short)   → FM mode
+ */
+
+#ifndef APP_MODE_H
+#define APP_MODE_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+/* Operating modes */
+typedef enum {
+    MODE_VFO = 0,
+    MODE_POCSAG,
+    MODE_SPECTRUM,
+    MODE_FM,
+    MODE_COUNT
+} op_mode_t;
+
+/* Get current mode */
+op_mode_t MODE_GetCurrent(void);
+
+/* Switch to a mode */
+void MODE_Switch(op_mode_t mode);
+
+/* Initialize mode dispatcher (call once at boot) */
+void MODE_Init(void);
+
+/* Call from 10ms timeslice */
+void MODE_TimeSlice10ms(void);
+
+/* Call from 500ms timeslice */
+void MODE_TimeSlice500ms(void);
+
+/* Process key press for mode switching.
+ * Returns true if the key was consumed by mode switch. */
+bool MODE_ProcessKey(int key, bool pressed, bool held);
+
+#endif