GPS driver (#55)

* u-blox GPS driver for both I2C and UART

gps/ublox.go

@@ -0,0 +1,53 @@
+package gps
+
+import (
+	"errors"
+	"time"
+)
+
+// flight mode disables the GPS COCOM limits
+var flight_mode_cmd = [...]byte{
+	0xB5, 0x62, 0x06, 0x24, 0x24, 0x00, 0xFF, 0xFF, 0x06, 0x03, 0x00, 0x00, 0x00,
+	0x00, 0x10, 0x27, 0x00, 0x00, 0x05, 0x00, 0xFA, 0x00, 0xFA, 0x00, 0x64, 0x00,
+	0x2C, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x16, 0xDC}
+
+// Sets CFG-GNSS to disable everything other than GPS GNSS
+// solution. Failure to do this means GPS power saving
+// doesn't work. Not needed for MAX7, needed for MAX8's
+var cfg_gnss_cmd = [...]byte{
+	0xB5, 0x62, 0x06, 0x3E, 0x2C, 0x00, 0x00, 0x00,
+	0x20, 0x05, 0x00, 0x08, 0x10, 0x00, 0x01, 0x00,
+	0x01, 0x01, 0x01, 0x01, 0x03, 0x00, 0x00, 0x00,
+	0x01, 0x01, 0x03, 0x08, 0x10, 0x00, 0x00, 0x00,
+	0x01, 0x01, 0x05, 0x00, 0x03, 0x00, 0x00, 0x00,
+	0x01, 0x01, 0x06, 0x08, 0x0E, 0x00, 0x00, 0x00,
+	0x01, 0x01, 0xFC, 0x11}
+
+func FlightMode(gpsDevice GPSDevice) (err error) {
+	err = sendCommand(gpsDevice, flight_mode_cmd[:])
+	return err
+}
+
+func SetCfgGNSS(gpsDevice GPSDevice) (err error) {
+	err = sendCommand(gpsDevice, cfg_gnss_cmd[:])
+	return err
+}
+
+func sendCommand(gpsDevice GPSDevice, command []byte) (err error) {
+	gpsDevice.WriteBytes(command)
+	start := time.Now()
+	for time.Now().Sub(start) < 1000 {
+		if gpsDevice.readNextByte() == '\n' {
+			if gpsDevice.readNextByte() == 0xB5 {
+				gpsDevice.readNextByte()
+				if gpsDevice.readNextByte() == 0x05 {
+					if gpsDevice.readNextByte() == 0x01 {
+						return
+					}
+				}
+			}
+		}
+	}
+	return errors.New("No ACK to GPS command")
+}