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/display_rssi.c

@@ -0,0 +1,128 @@
+/* UA1ZBE Custom Firmware - RSSI Display Implementation
+ *
+ * Reads RSSI from BK4819 REG_67 (9-bit value).
+ * Conversion: dBm = (raw / 2) - 160 + band_correction
+ *
+ * Displays as "S:XX" format with optional mini bar.
+ * Updates every ~150ms via internal counter.
+ */
+
+#include "display_rssi.h"
+#include "driver/bk4819.h"
+#include "driver/st7565.h"
+#include "ui/helper.h"
+#include "ui/main.h"
+#include "misc.h"
+#include "radio.h"
+#include <string.h>
+#include <stdio.h>
+
+/* dBm correction table — defined in ui/main.c */
+extern const int8_t dBmCorrTable[7];
+
+/* === Internal state === */
+
+static int16_t  s_rssi_dbm;
+static uint16_t s_rssi_raw;
+static uint8_t  s_s_level;
+static uint16_t s_update_counter;
+
+/* Update interval: ~15 (150ms at 10ms tick) */
+#define RSSI_UPDATE_INTERVAL  15
+
+/* S-meter thresholds (dBm) — simplified from U8RssiMap */
+static const int8_t s_thresholds[] = {
+    -121, -115, -109, -103, -97, -91, -85, -79, -73, -63
+};
+
+void RSSI_Init(void)
+{
+    s_rssi_dbm = -160;
+    s_rssi_raw = 0;
+    s_s_level = 0;
+    s_update_counter = 0;
+}
+
+void RSSI_Update(void)
+{
+    s_update_counter++;
+    if (s_update_counter < RSSI_UPDATE_INTERVAL)
+        return;
+    s_update_counter = 0;
+
+    /* Read raw RSSI from BK4819 */
+    s_rssi_raw = BK4819_GetRSSI();
+
+    /* Convert to dBm: (raw / 2) - 160 + band_correction
+     * Avoid division: raw >> 1 */
+    int8_t band_corr = dBmCorrTable[gRxVfo->Band];
+    s_rssi_dbm = (int16_t)(s_rssi_raw >> 1) - 160 + band_corr;
+
+    /* Calculate S-level */
+    s_s_level = 0;
+    for (uint8_t i = 0; i < ARRAY_SIZE(s_thresholds); i++) {
+        if (s_rssi_dbm >= s_thresholds[i]) {
+            s_s_level = i + 1;
+        }
+    }
+    if (s_s_level > 9)
+        s_s_level = 9;
+}
+
+int16_t RSSI_GetdBm(void)
+{
+    return s_rssi_dbm;
+}
+
+uint16_t RSSI_GetRaw(void)
+{
+    return s_rssi_raw;
+}
+
+uint8_t RSSI_GetSLevel(void)
+{
+    return s_s_level;
+}
+
+/*
+ * Draw RSSI indicator.
+ * Format: "S:42" or raw dBm with mini bar.
+ * Uses small font to fit in upper-right corner.
+ */
+void RSSI_Draw(int x, int y, bool with_bar)
+{
+    static char buf[16];
+
+    /* Draw dBm value: "-87dBm" */
+    sprintf(buf, "%ddBm", s_rssi_dbm);
+    UI_PrintStringSmallNormal(buf, x, LCD_WIDTH, y);
+
+    if (with_bar) {
+        /* Draw mini signal bar below the text
+         * 5 bars, each 2px wide, 1px gap */
+        int bar_x = x;
+        int bar_y = y + 8;
+        uint8_t bars = (s_s_level + 1) / 2;  /* 0-5 bars from S0-S9 */
+        if (bars > 5) bars = 5;
+
+        for (uint8_t i = 0; i < 5; i++) {
+            uint8_t h = 2 + i * 2;  /* Bar heights: 2,4,6,8,10 */
+            if (i < bars) {
+                /* Draw filled bar */
+                for (uint8_t py = 0; py < h; py++) {
+                    for (uint8_t px = 0; px < 2; px++) {
+                        UI_DrawPixelBuffer(gFrameBuffer, bar_x + i * 3 + px, bar_y + (10 - h) + py, true);
+                    }
+                }
+            } else {
+                /* Draw outline only */
+                UI_DrawPixelBuffer(gFrameBuffer, bar_x + i * 3,     bar_y + (10 - h),     false);
+                UI_DrawPixelBuffer(gFrameBuffer, bar_x + i * 3 + 1, bar_y + (10 - h),     false);
+                UI_DrawPixelBuffer(gFrameBuffer, bar_x + i * 3,     bar_y + 9,            false);
+                UI_DrawPixelBuffer(gFrameBuffer, bar_x + i * 3 + 1, bar_y + 9,            false);
+                UI_DrawPixelBuffer(gFrameBuffer, bar_x + i * 3,     bar_y + (10 - h) + 1, false);
+                UI_DrawPixelBuffer(gFrameBuffer, bar_x + i * 3 + 1, bar_y + (10 - h) + 1, false);
+            }
+        }
+    }
+}