Use Adafruit SdFat for GPS shield logging

Create up to 10,000 distinct long filenames with exclusive creation, drain startup GPS command replies before writing, and update CI and installation guidance for the Adafruit fork.

Co-authored-by: Limor Fried <ladyada@users.noreply.github.com>

examples/shield_sdlog/shield_sdlog.ino

@@ -1,7 +1,7 @@
 #include <SPI.h>
 #include <Adafruit_GPS.h>
 #include <SoftwareSerial.h>
-#include <SD.h>
+#include <SdFat_Adafruit_Fork.h>
 #include <avr/sleep.h>
 
 // Ladyada's logger modified by Bill Greiman to use the SdFat library
@@ -36,6 +36,7 @@ bool usingInterrupt = false;
 #define chipSelect 10
 #define ledPin 13
 
+SdFat SD;
 File logfile;
 
 // read a Hex value and return the decimal equivalent
@@ -96,18 +97,19 @@ void setup() {
     error(2);
   }
   char filename[15];
-  strcpy(filename, "GPSLOG00.TXT");
-  for (uint8_t i = 0; i < 100; i++) {
-    filename[6] = '0' + i/10;
-    filename[7] = '0' + i%10;
-    // create if does not exist, do not open existing, write, sync after write
+  strcpy(filename, "GPSLOG0000.TXT");
+  for (uint16_t i = 0; i < 10000; i++) {
+    filename[6] = '0' + i/1000;
+    filename[7] = '0' + (i/100)%10;
+    filename[8] = '0' + (i/10)%10;
+    filename[9] = '0' + i%10;
+    // Find an unused long filename, then create it without opening an old log.
     if (! SD.exists(filename)) {
       break;
     }
   }
 
-  logfile = SD.open(filename, FILE_WRITE);
-  if( ! logfile ) {
+  if (!logfile.open(filename, O_WRONLY | O_CREAT | O_EXCL)) {
     Serial.print(F("Couldnt create "));
     Serial.println(filename);
     error(3);
@@ -131,6 +133,16 @@ void setup() {
   GPS.sendCommand(F(PGCMD_NOANTENNA));
   GPS.sendCommand(F(CDCMD_NOANTENNA));
 
+  // Drain startup command replies before the first SD write. Their rapid
+  // arrival can otherwise reuse a GPS receive buffer while it is being saved.
+  uint32_t start = millis();
+  while (millis() - start < 2000) {
+    GPS.read();
+    if (GPS.newNMEAreceived()) {
+      GPS.lastNMEA();
+    }
+  }
+
   // the nice thing about this code is you can have a timer0 interrupt go off
   // every 1 millisecond, and read data from the GPS for you. that makes the
   // loop code a heck of a lot easier!