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)

functions.h

@@ -0,0 +1,42 @@
+/* Copyright 2023 Dual Tachyon
+ * https://github.com/DualTachyon
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ */
+
+#ifndef FUNCTIONS_H
+#define FUNCTIONS_H
+
+#include <stdint.h>
+
+enum FUNCTION_Type_t
+{
+	FUNCTION_FOREGROUND = 0,  // ???
+	FUNCTION_TRANSMIT,        // transmitting
+	FUNCTION_MONITOR,         // receiving with squelch forced open
+	FUNCTION_INCOMING,        // receiving a signal (squelch is open)
+	FUNCTION_RECEIVE,         // RX mode, squelch closed
+	FUNCTION_POWER_SAVE,      // sleeping
+	FUNCTION_BAND_SCOPE,      // bandscope mode (panadpter/spectrum) .. not yet implemented
+	FUNCTION_N_ELEM
+};
+
+typedef enum FUNCTION_Type_t FUNCTION_Type_t;
+
+extern FUNCTION_Type_t       gCurrentFunction;
+
+void FUNCTION_Init(void);
+void FUNCTION_Select(FUNCTION_Type_t Function);
+bool FUNCTION_IsRx();
+
+#endif