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/fm.h

@@ -0,0 +1,61 @@
+/* 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 APP_FM_H
+#define APP_FM_H
+
+#ifdef ENABLE_FMRADIO
+
+#include "driver/keyboard.h"
+
+#define FM_CHANNEL_UP	0x01
+#define FM_CHANNEL_DOWN	0xFF
+
+enum {
+	FM_SCAN_OFF = 0U,
+};
+
+extern uint16_t          gFM_Channels[20];
+extern bool              gFmRadioMode;
+extern uint8_t           gFmRadioCountdown_500ms;
+extern volatile uint16_t gFmPlayCountdown_10ms;
+extern volatile int8_t   gFM_ScanState;
+extern bool              gFM_AutoScan;
+extern uint8_t           gFM_ChannelPosition;
+// Doubts about          whether this should be signed or not
+extern uint16_t          gFM_FrequencyDeviation;
+extern bool              gFM_FoundFrequency;
+extern uint16_t          gFM_RestoreCountdown_10ms;
+
+bool    FM_CheckValidChannel(uint8_t Channel);
+// returns first valid channel starting at Channel
+uint8_t FM_FindNextChannel(uint8_t Channel, uint8_t Direction);
+int     FM_ConfigureChannelState(void);
+void    FM_TurnOff(void);
+void    FM_EraseChannels(void);
+
+void    FM_Tune(uint16_t Frequency, int8_t Step, bool bFlag);
+void    FM_PlayAndUpdate(void);
+int     FM_CheckFrequencyLock(uint16_t Frequency, uint16_t LowerLimit);
+
+void    FM_ProcessKeys(KEY_Code_t Key, bool bKeyPressed, bool bKeyHeld);
+
+void    FM_Play(void);
+void    FM_Start(void);
+
+#endif
+
+#endif