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)

ui/inputbox.c

@@ -0,0 +1,44 @@
+/* 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.
+ */
+
+#include <string.h>
+
+#include "ui/inputbox.h"
+
+char    gInputBox[8];
+char    inputBoxAscii[9];
+uint8_t gInputBoxIndex;
+
+void INPUTBOX_Append(const KEY_Code_t Digit)
+{
+	if (gInputBoxIndex >= sizeof(gInputBox))
+		return;
+
+	if (gInputBoxIndex == 0)
+		memset(gInputBox, 10, sizeof(gInputBox));
+
+	if (Digit != KEY_INVALID)
+		gInputBox[gInputBoxIndex++] = (char)(Digit - KEY_0);
+}
+
+const char* INPUTBOX_GetAscii()
+{
+	for(int i = 0; i < 8; i++) {
+		char c = gInputBox[i];
+		inputBoxAscii[i] = (c==10)? '-' : '0' + c;
+	}
+	return inputBoxAscii;
+}