Using signed 32-bit data type for RSSI instead of floating points

Switched to int32_t for RSSI representation to allow running the code also
on devices with limited resources. Defined a new ad-hoc type to still keep
the possibility of using floating points on more capable devices.

openrtx/include/core/datatypes.h

@@ -45,6 +45,13 @@ typedef unsigned int tone_t;
  */
 typedef uint32_t freq_t;
 
+/**
+ * \brief RSSI type.
+ *
+ * Data type for RSSI, in dBm.
+ */
+typedef int32_t rssi_t;
+
 #ifdef __cplusplus
 }
 #endif

openrtx/include/core/graphics.h

@@ -20,6 +20,7 @@
 #ifndef GRAPHICS_H
 #define GRAPHICS_H
 
+#include <datatypes.h>
 #include <symbols.h>
 #include <stdbool.h>
 #include <stddef.h>
@@ -307,7 +308,7 @@ void gfx_drawBattery(point_t start, uint16_t width, uint16_t height,
  * @param drawVolume: whether the volume bar should be drawn
  * @param color: color of the squelch bar
  */
-void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, float rssi,
+void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, rssi_t rssi,
                     uint8_t squelch, uint8_t volume, bool drawVolume, color_t color);
 
 /**
@@ -323,7 +324,7 @@ void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, float rssi,
  * @param drawVolume: whether the volume bar should be drawn
  */
 void gfx_drawSmeterLevel(point_t start, uint16_t width, uint16_t height,
-                         float rssi, uint8_t level, uint8_t volume, bool drawVolume);
+                         rssi_t rssi, uint8_t level, uint8_t volume, bool drawVolume);
 
 /**
  * Function to draw GPS SNR bar graph of arbitrary size.

openrtx/include/core/state.h

@@ -39,7 +39,7 @@ typedef struct
     datetime_t time;
     uint16_t   v_bat;
     uint8_t    charge;
-    float      rssi;
+    rssi_t     rssi;
 
     uint8_t    ui_screen;
     uint8_t    tuner_mode;

openrtx/include/interfaces/radio.h

@@ -124,7 +124,7 @@ void radio_updateConfiguration();
  *
  * @return RSSI level in dBm.
  */
-float radio_getRssi();
+rssi_t radio_getRssi();
 
 /**
  * Get the current operating status of the radio module.

openrtx/include/rtx/rtx.h

@@ -138,7 +138,7 @@ void rtx_task();
  * Get current RSSI in dBm.
  * @return RSSI value in dBm.
  */
-float rtx_getRssi();
+rssi_t rtx_getRssi();
 
 /**
  * Get current status of the RX squelch. This function is thread-safe and can

openrtx/src/core/graphics.c

@@ -740,7 +740,7 @@ void gfx_drawBattery(point_t start, uint16_t width, uint16_t height,
  * Width (px)
  *
  */
-void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, float rssi,
+void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, rssi_t rssi,
                     uint8_t squelch, uint8_t volume, bool drawVolume, color_t color)
 {
     color_t white =  {255, 255, 255, 255};
@@ -794,9 +794,9 @@ void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, float rssi,
 
     // RSSI bar
     uint16_t rssi_height = bar_height * 4 / bar_height_divider;
-    float s_level =  (127.0f + rssi) / 6.0f;
+    int16_t  s_level =  (127 + rssi) / 6;
-    uint16_t rssi_width = (s_level < 0.0f) ? 0 : (s_level * (width - 1) / 11);
+    uint16_t rssi_width = (s_level < 0) ? 0 : (s_level * (width - 1) / 11);
-    rssi_width = (s_level > 10.0f) ? width : rssi_width;
+    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);
 }
@@ -826,7 +826,7 @@ void gfx_drawSmeter(point_t start, uint16_t width, uint16_t height, float rssi,
  * Width (px)
  *
  */
-void gfx_drawSmeterLevel(point_t start, uint16_t width, uint16_t height, float rssi,
+void gfx_drawSmeterLevel(point_t start, uint16_t width, uint16_t height, rssi_t rssi,
                          uint8_t level, uint8_t volume, bool drawVolume)
 {
     color_t red =    {255, 0,   0  , 255};
@@ -863,10 +863,10 @@ void gfx_drawSmeterLevel(point_t start, uint16_t width, uint16_t height, float r
     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
-    float s_level =  (127.0f + rssi) / 6.0f;
+    int16_t  s_level =  (127 + rssi) / 6;
     uint16_t rssi_height = bar_height * 3 / bar_height_divider;
-    uint16_t rssi_width = (s_level < 0.0f) ? 0 : (s_level * (width - 1) / 11);
+    uint16_t rssi_width = (s_level < 0) ? 0 : (s_level * (width - 1) / 11);
-    rssi_width = (s_level > 10.0f) ? width : rssi_width;
+    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/rtx/OpMode_FM.cpp

@@ -103,13 +103,13 @@ void OpMode_FM::update(rtxStatus_t *const status, const bool newCfg)
     {
         // RF squelch mechanism
         // This turns squelch (0 to 15) into RSSI (-127.0dbm to -61dbm)
-        float squelch = -127.0f + status->sqlLevel * 66.0f / 15.0f;
+        rssi_t squelch = -127 + (status->sqlLevel * 66) / 15;
-        float rssi    = rtx_getRssi();
+        rssi_t rssi    = rtx_getRssi();
 
         // Provide a bit of hysteresis, only change state if the RSSI has
-        // moved more than .1dbm on either side of the current squelch setting.
+        // moved more than 1dBm on either side of the current squelch setting.
-        if((rfSqlOpen == false) && (rssi > (squelch + 0.1f))) rfSqlOpen = true;
+        if((rfSqlOpen == false) && (rssi > (squelch + 1))) rfSqlOpen = true;
-        if((rfSqlOpen == true)  && (rssi < (squelch - 0.1f))) rfSqlOpen = false;
+        if((rfSqlOpen == true)  && (rssi < (squelch - 1))) rfSqlOpen = false;
 
         // Local flags for current RF and tone squelch status
         bool rfSql   = ((status->rxToneEn == 0) && (rfSqlOpen == true));

openrtx/src/rtx/rtx.cpp

@@ -28,7 +28,7 @@
 static pthread_mutex_t   *cfgMutex;     // Mutex for incoming config messages
 static const rtxStatus_t *newCnf;       // Pointer for incoming config messages
 static rtxStatus_t        rtxStatus;    // RTX driver status
-static float              rssi;         // Current RSSI in dBm
+static rssi_t             rssi;         // Current RSSI in dBm
 static bool               reinitFilter; // Flag for RSSI filter re-initialisation
 
 static OpMode  *currMode;               // Pointer to currently active opMode handler
@@ -190,7 +190,13 @@ void rtx_task()
         {
             if(!reinitFilter)
             {
-                rssi = 0.74*radio_getRssi() + 0.26*rssi;
+                /*
+                 * Filter RSSI value using 15.16 fixed point math. Equivalent
+                 * floating point code is: rssi = 0.74*radio_getRssi() + 0.26*rssi
+                 */
+                int32_t filt_rssi = radio_getRssi() * 0xBD70    // 0.74 * radio_getRssi
+                                  + rssi            * 0x428F;   // 0.26 * rssi
+                rssi = (filt_rssi + 32768) >> 16;               // Round to nearest
             }
             else
             {
@@ -213,7 +219,7 @@ void rtx_task()
     currMode->update(&rtxStatus, reconfigure);
 }
 
-float rtx_getRssi()
+rssi_t rtx_getRssi()
 {
     return rssi;
 }

openrtx/src/ui/default/ui_main.c

@@ -260,7 +260,7 @@ void _ui_drawVFOMiddleInput(ui_state_t* ui_state)
 void _ui_drawMainBottom()
 {
     // Squelch bar
-    float rssi = last_state.rssi;
+    rssi_t   rssi = last_state.rssi;
     uint8_t  squelch = last_state.settings.sqlLevel;
     uint8_t  volume = platform_getVolumeLevel();
     uint16_t meter_width = CONFIG_SCREEN_WIDTH - 2 * layout.horizontal_pad;

openrtx/src/ui/default/ui_menu.c

@@ -516,7 +516,7 @@ int _ui_getInfoValueName(char *buf, uint8_t max_len, uint8_t index)
             snprintf(buf, max_len, "%d%%", last_state.charge);
             break;
         case 3: // RSSI
-            snprintf(buf, max_len, "%.1fdBm", last_state.rssi);
+            snprintf(buf, max_len, "%ddBm", last_state.rssi);
             break;
         case 4: // Heap usage
             snprintf(buf, max_len, "%dB", getHeapSize() - getCurrentFreeHeap());

platform/drivers/baseband/radio_GDx.cpp

@@ -369,9 +369,9 @@ void radio_updateConfiguration()
     if(radioStatus == TX) radio_enableTx();
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
-    return static_cast< float >(at1846s.readRSSI());
+    return static_cast< rssi_t > (at1846s.readRSSI());
 }
 
 enum opstatus radio_getStatus()

platform/drivers/baseband/radio_MD3x0.cpp

@@ -397,7 +397,7 @@ void radio_updateConfiguration()
     if(radioStatus == TX) radio_enableTx();
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
     /*
      * On MD3x0 devices, RSSI value is get by reading the analog RSSI output
@@ -415,7 +415,7 @@ float radio_getRssi()
 
     float rssi_mv  = ((float) adc1_getMeasurement(ADC_RSSI_CH));
     float rssi_dbm = (rssi_mv - rssi_offset[offset_index]) / rssi_gain;
-    return rssi_dbm;
+    return static_cast< rssi_t >(rssi_dbm);
 }
 
 enum opstatus radio_getStatus()

platform/drivers/baseband/radio_MD9600.cpp

@@ -76,7 +76,7 @@ void radio_updateConfiguration()
 
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
     return -154.0f;
 }

platform/drivers/baseband/radio_Mod17.cpp

@@ -99,7 +99,7 @@ void radio_updateConfiguration()
 
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
     return -123.0f;
 }

platform/drivers/baseband/radio_UV3x0.cpp

@@ -366,9 +366,9 @@ void radio_updateConfiguration()
     if(radioStatus == TX) radio_enableTx();
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
-    return static_cast< float > (at1846s.readRSSI());
+    return static_cast< rssi_t >(at1846s.readRSSI());
 }
 
 enum opstatus radio_getStatus()

platform/drivers/baseband/radio_linux.cpp

@@ -78,11 +78,11 @@ void radio_updateConfiguration()
     puts("radio_linux: updateConfiguration() called");
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
     // Commented to reduce verbosity on Linux
     // printf("radio_linux: requested RSSI at freq %d, returning -100dBm\n", rxFreq);
-    return emulator_state.RSSI;
+    return static_cast< rssi_t >(emulator_state.RSSI);
 }
 
 enum opstatus radio_getStatus()

platform/drivers/baseband/radio_ttwrplus.cpp

@@ -181,9 +181,9 @@ void radio_updateConfiguration()
     if(radioStatus == TX) radio_enableTx();
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
-    return static_cast< float > (at1846s.readRSSI());
+    return static_cast< rssi_t > (at1846s.readRSSI());
 }
 
 enum opstatus radio_getStatus()

platform/drivers/stubs/radio_stub.c

@@ -67,7 +67,7 @@ void radio_updateConfiguration()
 
 }
 
-float radio_getRssi()
+rssi_t radio_getRssi()
 {
     return -121.0f;  // S1 level: -121dBm
 }