Add Mute action

app/action.c

@@ -111,6 +111,7 @@ void (*action_opt_table[])(void) = {
     [ACTION_OPT_PTT] = &ACTION_Ptt,
     [ACTION_OPT_WN] = &ACTION_Wn,
     [ACTION_OPT_BACKLIGHT] = &ACTION_BackLight,
+    [ACTION_OPT_MUTE] = &ACTION_Mute,
     #ifdef ENABLE_FEAT_F4HWN_RESCUE_OPS
         [ACTION_OPT_POWER_HIGH] = &ACTION_Power_High,
         [ACTION_OPT_REMOVE_OFFSET] = &ACTION_Remove_Offset,
@@ -625,6 +626,25 @@ void ACTION_BackLightOnDemand(void)
     BACKLIGHT_TurnOn();
 }
 
+void ACTION_Mute(void)
+{
+    // Toggle mute state
+    gMute = !gMute;
+
+    // Update the registers
+    #ifdef ENABLE_FMRADIO
+        BK1080_WriteRegister(BK1080_REG_05_SYSTEM_CONFIGURATION2, gMute ? 0x0A10 : 0x0A1F);
+    #endif
+    gEeprom.VOLUME_GAIN = gMute ? 0 : gEeprom.VOLUME_GAIN_BACKUP;
+    BK4819_WriteRegister(BK4819_REG_48,
+        (11u << 12)                |  // ??? .. 0 ~ 15, doesn't seem to make any difference
+        (0u << 10)                 |  // AF Rx Gain-1
+        (gEeprom.VOLUME_GAIN << 4) |  // AF Rx Gain-2
+        (gEeprom.DAC_GAIN << 0));     // AF DAC Gain (after Gain-1 and Gain-2)
+
+    gUpdateStatus = true;
+}
+
     #ifdef ENABLE_FEAT_F4HWN_RESCUE_OPS
     void ACTION_Power_High(void)
     {