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)

frequencies.h

@@ -0,0 +1,93 @@
+/* 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 FREQUENCIES_H
+#define FREQUENCIES_H
+
+#include <stdint.h>
+
+#define _1GHz_in_KHz 100000000
+
+typedef struct {
+	const uint32_t lower;
+	const uint32_t upper;
+} freq_band_table_t;
+
+extern const freq_band_table_t BX4819_band1;
+extern const freq_band_table_t BX4819_band2;
+
+typedef enum  {
+	BAND_NONE = -1,
+	BAND1_50MHz = 0,
+	BAND2_108MHz,
+	BAND3_137MHz,
+	BAND4_174MHz,
+	BAND5_350MHz,
+	BAND6_400MHz,
+	BAND7_470MHz,
+	BAND_N_ELEM
+} FREQUENCY_Band_t;
+
+extern const freq_band_table_t frequencyBandTable[];
+
+typedef enum {
+// standard steps
+	STEP_2_5kHz,
+	STEP_5kHz,
+	STEP_6_25kHz,
+	STEP_10kHz,
+	STEP_12_5kHz,
+	STEP_25kHz,
+	STEP_8_33kHz,
+// custom steps
+	STEP_0_01kHz,
+	STEP_0_05kHz,
+	STEP_0_1kHz,
+	STEP_0_25kHz,
+	STEP_0_5kHz,
+	STEP_1kHz,
+	STEP_1_25kHz,
+	STEP_9kHz,
+	STEP_15kHz,
+	STEP_20kHz,
+	STEP_30kHz,
+	STEP_50kHz,
+	STEP_100kHz,
+	STEP_125kHz,
+	STEP_200kHz,
+	STEP_250kHz,
+	STEP_500kHz,
+	STEP_N_ELEM
+} STEP_Setting_t;
+
+
+extern const uint16_t gStepFrequencyTable[];
+
+#ifdef ENABLE_NOAA
+	extern const uint32_t NoaaFrequencyTable[10];
+#endif
+
+FREQUENCY_Band_t FREQUENCY_GetBand(uint32_t Frequency);
+uint8_t          FREQUENCY_CalculateOutputPower(uint8_t TxpLow, uint8_t TxpMid, uint8_t TxpHigh, int32_t LowerLimit, int32_t Middle, int32_t UpperLimit, int32_t Frequency);
+uint32_t 		 FREQUENCY_RoundToStep(uint32_t freq, uint16_t step);
+
+STEP_Setting_t   FREQUENCY_GetStepIdxFromSortedIdx(uint8_t sortedIdx);
+uint32_t		 FREQUENCY_GetSortedIdxFromStepIdx(uint8_t step);
+
+int32_t          TX_freq_check(uint32_t Frequency);
+int32_t          RX_freq_check(uint32_t Frequency);
+
+#endif