From 16df1ad58468c8952452ae6d50e268c7694c384e Mon Sep 17 00:00:00 2001
From: Jeff Epler <jepler@unpythonic.net>
Date: Fri, 6 Jul 2018 07:05:51 -0500
Subject: [PATCH] Support setting frequency via serial

To set the frequency, connect via serial and enter e.g.,:
    F1M
followed by enter/return to set the frequency to 1000000Hz (1MHz)

Frequency can be set as a whole number, a whole number of kHz, or a
whole number of MHz.  The commands are case insensitive.  So all
the following set the frequency to 1MHz:
    F1000000
    F1000k
    F1M

No validation is performed and nonsensical things can be requested,
so for example if you enter the nonsensical "F9MMM", you get
"GPS Initialized to output RF at 3800301568"  This specific number
results from overflow of integer arithmetic and is also way out of
spec for the board, since the actual value requested is around 3.8GHz.
---
 RFout1MHzV1_05/RFout1MHzV1_05.ino | 34 +++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/RFout1MHzV1_05/RFout1MHzV1_05.ino b/RFout1MHzV1_05/RFout1MHzV1_05.ino
index f0f85d3..ef5cdec 100644
--- a/RFout1MHzV1_05/RFout1MHzV1_05.ino
+++ b/RFout1MHzV1_05/RFout1MHzV1_05.ino
@@ -15,6 +15,8 @@ SoftwareSerial gpsPort(2, 3); // RX, TX
 #define FIXOut 4         //Pin Out at IDC. Indicator for GPS Lock on pin 4
 #define LDO_Enable A3    //GPS Voltage regulator Enable on pin A3
 boolean GPSOK, passthrough;
+int state; // serial command state machine
+uint32_t freq; // Frequency in Hz commanded via serial
 #define softwareversion "1.05" //Version of this program, sent to serialport at startup
 NMEAGPS  gps; // This parses the GPS characters
 gps_fix  fix; // This holds on to the latest values
@@ -91,6 +93,37 @@ void handle_serial() {
     Serial.println(F("Entering passthrough mode -- reset microcontroller to return to normal mode\n"));
     passthrough = true;
   }
+  else if(c == 'F' || c == 'f') {
+    Serial.print(F("Frequency?"));
+    state = 1; freq = 0;
+  }
+  else if(state == 1) {
+    if(c >= '0' && c <= '9') {
+      Serial.write(c);
+      freq = freq * 10 + c - '0';
+    } else if (c == 'M' || c == 'm') {
+      Serial.write(c);
+      freq *= 1000000lu;
+    } else if (c == 'K' || c == 'k') {
+      Serial.write(c);
+      freq *= 1000lu;
+    } else if (c == '\n' || c == '\r') {
+      Serial.println(F(""));
+      if (setGPS_OutputFreq(freq)) {
+        Serial.print ("GPS Initialized to output RF at " );
+        Serial.println (freq);
+        Serial.println ("Initialization is complete.");
+        Serial.println ("");
+        GPSOK = true;
+      }
+      else
+      {
+        Serial.println (F("Error! Could not program GPS!"));
+        GPSOK = false;
+      }
+      state = 0;
+    }
+  }
 }
 
 
@@ -105,6 +138,7 @@ void loop()
   if(Serial.available()) {
     handle_serial();
   }
+  if(state != 0) return;
   while (gps.available( gpsPort )) {
     fix = gps.read();
     if (fix.valid.location && fix.valid.date && fix.valid.time)