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)

firmware.ld

@@ -0,0 +1,79 @@
+ENTRY(HandlerReset)
+
+_estack = 0x20004000;    /* end of 16K RAM */
+
+_Min_Heap_Size = 0;      /* required amount of heap  */
+_Min_Stack_Size = 0x80;  /* required amount of stack */
+
+MEMORY
+{
+	FLASH (rx)      : ORIGIN = 0x00000000, LENGTH = 60K
+	RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 16K
+}
+
+SECTIONS
+{
+	/* Program code */
+	.text :
+	{
+		. = ALIGN(4);
+		KEEP(*(.text.isr)) /* .text sections of code  */
+		*(.text)           /* .text sections of code  */
+		*(.text*)          /* .text* sections of code */
+		*(.rodata)         /* .rodata sections        */
+		*(.rodata*)        /* .rodata* sections       */
+		*(.glue_7)         /* Glue arm to thumb code  */
+		*(.glue_7t)        /* Glue thumb to arm code  */
+		*(.eh_frame)
+
+		KEEP(*(.fini))
+		. = ALIGN(4);
+		_etext = .;        /* global symbols at end   */
+	} >FLASH
+
+	/* Used by startup code */
+
+	. = ALIGN(4);
+
+	flash_data_start = .;
+
+	.data :
+	{
+		. = ALIGN(4);
+		sram_data_start = .;
+		*(.sramtext)
+		*(.srambss)
+		*(.data)           /* .data sections              */
+		*(.data*)          /* .data* sections             */
+
+		. = ALIGN(4);
+		_edata = .;        /* Global symbol at data end   */
+	} >RAM AT> FLASH
+
+	sram_data_end = .;
+
+	/* Uninitialized data */
+	. = ALIGN(4);
+	.bss :
+	{
+		_sbss = .;         /* Global symbol at bss start */
+		__bss_start__ = _sbss;
+		*(.bss)
+		*(.bss*)
+		*(COMMON)
+
+		. = ALIGN(4);
+		_ebss = .;         /* Global symbol at bss end */
+		__bss_end__ = _ebss;
+	} >RAM
+
+	/* Check that there is enough RAM */
+	._user_heap_stack :
+	{
+		. = ALIGN(4);
+		. = . + _Min_Heap_Size;
+		. = . + _Min_Stack_Size;
+		. = ALIGN(4);
+	} >RAM
+}
+