diff --git a/libraries/SITL/SIM_last_letter.cpp b/libraries/SITL/SIM_last_letter.cpp
new file mode 100644
index 0000000000..abcaf56a84
--- /dev/null
+++ b/libraries/SITL/SIM_last_letter.cpp
@@ -0,0 +1,129 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+ */
+/*
+ simulator connector for ardupilot version of last_letter
+*/
+
+#include
+#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
+#include "SIM_last_letter.h"
+#include
+#include
+#include
+#include
+
+extern const AP_HAL::HAL& hal;
+
+/*
+ constructor
+ */
+last_letter::last_letter(const char *home_str, const char *frame_str) :
+ Aircraft(home_str, frame_str),
+ last_timestamp_us(0),
+ sock(true)
+{
+ // try to bind to a specific port so that if we restart ArduPilot
+ // last_letter keeps sending us packets. Not strictly necessary but
+ // useful for debugging
+ sock.bind("127.0.0.1", fdm_port+1);
+
+ sock.reuseaddress();
+ sock.set_blocking(false);
+
+ start_last_letter();
+}
+
+/*
+ start last_letter child
+ */
+void last_letter::start_last_letter(void)
+{
+ pid_t child_pid = fork();
+ if (child_pid == 0) {
+ close(0);
+ open("/dev/null", O_RDONLY);
+ // in child
+ for (uint8_t i=3; i<100; i++) {
+ close(i);
+ }
+
+ int ret = execlp("roslaunch",
+ "roslaunch",
+ "last_letter",
+ "launcher.launch",
+ "ArduPlane:=true",
+ NULL);
+ if (ret != 0) {
+ perror("roslaunch");
+ }
+ exit(1);
+ }
+}
+
+/*
+ send servos
+*/
+void last_letter::send_servos(const struct sitl_input &input)
+{
+ servo_packet pkt;
+ memcpy(pkt.servos, input.servos, sizeof(pkt.servos));
+ sock.sendto(&pkt, sizeof(pkt), "127.0.0.1", fdm_port);
+}
+
+/*
+ receive an update from the FDM
+ This is a blocking function
+ */
+void last_letter::recv_fdm(const struct sitl_input &input)
+{
+ fdm_packet pkt;
+
+ /*
+ we re-send the servo packet every 0.1 seconds until we get a
+ reply. This allows us to cope with some packet loss to the FDM
+ */
+ while (sock.recv(&pkt, sizeof(pkt), 100) != sizeof(pkt)) {
+ send_servos(input);
+ }
+
+ accel_body = Vector3f(pkt.xAccel, pkt.yAccel, pkt.zAccel);
+ gyro = Vector3f(pkt.rollRate, pkt.pitchRate, pkt.yawRate);
+ velocity_ef = Vector3f(pkt.speedN, pkt.speedE, pkt.speedD);
+ location.lat = pkt.latitude * 1.0e7;
+ location.lng = pkt.longitude * 1.0e7;
+ location.alt = pkt.altitude*1.0e2;
+ dcm.from_euler(pkt.roll, pkt.pitch, pkt.yaw);
+
+ // auto-adjust to last_letter frame rate
+ uint64_t deltat_us = pkt.timestamp_us - last_timestamp_us;
+ time_now_us += deltat_us;
+
+ if (deltat_us < 1.0e4 && deltat_us > 0) {
+ adjust_frame_time(1.0e6/deltat_us);
+ }
+ last_timestamp_us = pkt.timestamp_us;
+}
+
+/*
+ update the last_letter simulation by one time step
+ */
+void last_letter::update(const struct sitl_input &input)
+{
+ send_servos(input);
+ recv_fdm(input);
+ sync_frame_time();
+}
+#endif // CONFIG_HAL_BOARD
diff --git a/libraries/SITL/SIM_last_letter.h b/libraries/SITL/SIM_last_letter.h
new file mode 100644
index 0000000000..da3c7efd8c
--- /dev/null
+++ b/libraries/SITL/SIM_last_letter.h
@@ -0,0 +1,76 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+ */
+/*
+ simulator connection for ardupilot version of last_letter
+*/
+
+#ifndef _SIM_LAST_LETTER_H
+#define _SIM_LAST_LETTER_H
+
+#include "SIM_Aircraft.h"
+#include
+
+/*
+ a last_letter simulator
+ */
+class last_letter : public Aircraft
+{
+public:
+ last_letter(const char *home_str, const char *frame_str);
+
+ /* update model by one time step */
+ void update(const struct sitl_input &input);
+
+ /* static object creator */
+ static Aircraft *create(const char *home_str, const char *frame_str) {
+ return new last_letter(home_str, frame_str);
+ }
+
+private:
+ static const uint16_t fdm_port = 9002;
+
+ /*
+ packet sent to last_letter
+ */
+ struct servo_packet {
+ uint16_t servos[16];
+ };
+
+ /*
+ reply packet sent from last_letter to ArduPilot
+ */
+ struct fdm_packet {
+ uint64_t timestamp_us; // simulation time in microseconds
+ double latitude, longitude;
+ double altitude;
+ double heading;
+ double speedN, speedE, speedD;
+ double xAccel, yAccel, zAccel;
+ double rollRate, pitchRate, yawRate;
+ double roll, pitch, yaw;
+ double airspeed;
+ };
+
+ void recv_fdm(const struct sitl_input &input);
+ void send_servos(const struct sitl_input &input);
+ void start_last_letter(void);
+
+ uint64_t last_timestamp_us;
+ SocketAPM sock;
+};
+
+
+#endif // _SIM_LAST_LETTER_H