Reverted back to old si4468.c code

nanovna.h

@@ -76,6 +76,7 @@
 #define __LISTEN__
 #define __CHANNEL_POWER__
 #define __LIMITS__
+#define __MCU_CLOCK_SHIFT__
 #ifdef TINYSA4
 #define  __HARMONIC__
 #define __VBW__

plot.c

@@ -376,6 +376,23 @@ dBm_to_Watt(const float v)
   return   logf(v*1000.0)*(10.0/logf(10.0));
 }
 
+static float fast_expf(float x)
+{
+  union { float f; int32_t i; } v;
+  v.i = (int32_t)(12102203.0f*x) + 0x3F800000;
+  int32_t m = (v.i >> 7) & 0xFFFF;  // copy mantissa
+#if 1
+  // cubic spline approximation
+  // empirical values for small maximum relative error (8.34e-5):
+  v.i += ((((((((1277*m) >> 14) + 14825)*m) >> 14) - 79749)*m) >> 11) - 626;
+#else
+  // quartic spline approximation
+  // empirical values for small maximum relative error (1.21e-5):
+  v.i += (((((((((((3537*m) >> 16) + 13668)*m) >> 18) + 15817)*m) >> 14) - 80470)*m) >> 11);
+#endif
+  return v.f;
+}
+
 static void
 trace_into_index_x_array(index_x_t *x, uint16_t points){
   // Not need update if index calculated for this points count
@@ -417,7 +434,7 @@ trace_into_index_y_array(index_y_t *y, float *array, int points)
   int max = NGRIDY * GRIDY, i;
   for (i=0;i<points;i++){
     float value = array[i];
-    if (mult) value = expf(value*mult);
+    if (mult) value = fast_expf(value*mult);
     value = ref - value * scale;
     int v = value;
          if (v <   0) v = 0;

sa_core.c

@@ -2559,11 +2559,15 @@ pureRSSI_t perform(bool break_on_operation, int i, freq_t f, int tracking)     /
     }
     if (MODE_INPUT(setting.mode)) {
       calculate_static_correction();
+#ifdef __MCU_CLOCK_SHIFT__
       if (!in_selftest) clock_above_48MHz();
+#endif
       is_below = false;
       correct_RSSI_freq = get_frequency_correction(f);  // for i == 0 and freq_step == 0;
     } else {
+#ifdef __MCU_CLOCK_SHIFT__
       clock_at_48MHz();
+#endif
     }
     //    if (MODE_OUTPUT(setting.mode) && setting.additional_step_delay_us < 500)     // Minimum wait time to prevent LO from lockup during output frequency sweep
     //      setting.additional_step_delay_us = 500;
@@ -3226,7 +3230,7 @@ again:                                                              // Spur redu
 #endif
     }
 
-#if 1
+#ifdef __MCU_CLOCK_SHIFT__
         if (setting.mode == M_LOW && !in_selftest) {         // Avoid 48MHz spur
           int set_below = false;
 #ifdef TINYSA4
@@ -3239,6 +3243,7 @@ again:                                                              // Spur redu
 #endif
           if (lf > 40000000){
             uint32_t tf = lf;
+            while (tf > 240000000) tf -= 240000000;       // Wrap between 0-48MHz
             while (tf > 48000000) tf -= 48000000;       // Wrap between 0-48MHz
             if (tf < 20000000 )
               set_below = true;