UI: fixed RSSI to S-level conversion in gfx_drawSmeter and gfx_drawSmeterLevel

openrtx/include/core/utils.h

@@ -1,5 +1,5 @@
 /***************************************************************************
- *   Copyright (C) 2020 - 2023 by Federico Amedeo Izzo IU2NUO,             *
+ *   Copyright (C) 2020 - 2025 by Federico Amedeo Izzo IU2NUO,             *
  *                                Niccolò Izzo IU2KIN,                     *
  *                                Silvano Seva IU2KWO                      *
  *                                                                         *
@@ -17,8 +17,8 @@
  *   along with this program; if not, see <http://www.gnu.org/licenses/>   *
  ***************************************************************************/
 
-#ifndef CALIB_UTILS_H
+#ifndef UTILS_H
-#define CALIB_UTILS_H
+#define UTILS_H
 
 #include <datatypes.h>
 #include <stdint.h>
@@ -49,8 +49,10 @@ uint8_t interpCalParameter(const freq_t freq, const freq_t *calPoints,
                            const uint8_t *param, const uint8_t elems);
 
 /**
- * \internal Utility function to convert 4 byte BCD values into a 32-bit
+ * Convert a 4 byte BCD number to a 32-bit unsigned integer one.
- * unsigned integer ones.
+ *
+ * @param bcd: BCD number
+ * @return unsigned integer representation of the BCD input.
  */
 uint32_t bcdToBin(uint32_t bcd);
 
@@ -64,6 +66,14 @@ uint32_t bcdToBin(uint32_t bcd);
  */
 void stripTrailingZeroes(char *str);
 
+/**
+ * Get the S-level corresponding to a given RSSI value in dBm.
+ *
+ * @param rssi: RSSI in dBm
+ * @return S level, from S0 to S11
+ */
+uint8_t rssiToSlevel(const rssi_t rssi);
+
 #ifdef __cplusplus
 }
 #endif

openrtx/src/core/graphics.c

@@ -31,6 +31,7 @@
 #include <limits.h>
 #include <stdio.h>
 #include <math.h>
+#include <utils.h>
 
 #include <gfxfont.h>
 #include <TomThumb.h>
@@ -775,9 +776,7 @@ void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, rssi_t rssi,
 
     // RSSI bar
     uint16_t rssi_height = bar_height * 4 / bar_height_divider;
-    int16_t  s_level =  (127 + rssi) / 6;
+    uint16_t rssi_width = (rssiToSlevel(rssi) * (width - 1) / 11);
-    uint16_t rssi_width = (s_level < 0) ? 0 : (s_level * (width - 1) / 11);
-    rssi_width = (s_level > 10) ? width : rssi_width;
     point_t rssi_pos = { start.x, (uint8_t) (start.y + 2 + squelch_height + volume_height)};
     gfx_drawRect(rssi_pos, rssi_width, rssi_height, white, true);
 }
@@ -843,11 +842,10 @@ void gfx_drawSmeterLevel(point_t start, uint16_t width, uint16_t height, rssi_t
     uint16_t level_width = (width * level) / 255;
     point_t level_pos = { start.x, (uint8_t) (start.y + 2 + volume_height)};
     gfx_drawRect(level_pos, level_width, level_height, green, true);
+
     // RSSI bar
-    int16_t  s_level =  (127 + rssi) / 6;
     uint16_t rssi_height = bar_height * 3 / bar_height_divider;
-    uint16_t rssi_width = (s_level < 0) ? 0 : (s_level * (width - 1) / 11);
+    uint16_t rssi_width = (rssiToSlevel(rssi) * (width - 1) / 11);
-    rssi_width = (s_level > 10) ? width : rssi_width;
     point_t rssi_pos = {start.x, (uint8_t) (start.y + 5 + level_height + volume_height)};
     gfx_drawRect(rssi_pos, rssi_width, rssi_height, white, true);
     // S-level marks and numbers

openrtx/src/core/utils.c

@@ -1,5 +1,5 @@
 /***************************************************************************
- *   Copyright (C) 2020 - 2023 by Federico Amedeo Izzo IU2NUO,             *
+ *   Copyright (C) 2020 - 2025 by Federico Amedeo Izzo IU2NUO,             *
  *                                Niccolò Izzo IU2KIN,                     *
  *                                Silvano Seva IU2KWO                      *
  *                                                                         *
@@ -76,3 +76,21 @@ void stripTrailingZeroes(char *str)
         }
     }
 }
+
+uint8_t rssiToSlevel(const rssi_t rssi)
+{
+    // RSSI >= -53dB is S11 (S9 + 20 dB)
+    if(rssi >= -53)
+        return 11;
+
+    // RSSI lower than -121dB is always S0
+    if(rssi < -121)
+        return 0;
+
+    // For S level > 9 use 10dB steps instead of 6dB
+    if (rssi >= -73)
+        return (uint8_t)((163 + rssi) / 10);
+
+    // For S1 - S9 use 6dB increase per S-Point
+    return (uint8_t)(127 + rssi) / 6;
+}