SITL: add ELRS simulator

libraries/SITL/SIM_ELRS.cpp

@@ -0,0 +1,165 @@
+#include <AP_HAL/AP_HAL.h>
+
+// Only support ELRS simulation in SITL (not Sim on Hardware)
+#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
+
+#include "SIM_ELRS.h"
+#include <SITL/SITL.h>
+
+#include <AP_HAL_SITL/AP_HAL_SITL.h>
+#include <AP_HAL_SITL/UARTDriver.h>
+
+#include "include/mavlink/v2.0/all/mavlink.h"
+
+// Example command: -A --serial2=sim:ELRS
+// TCP connection will be started on normal AP port eg 5763 for serial 2
+
+// Baud rate must be set correctly
+// param set SERIAL2_BAUD 460
+
+using namespace SITL;
+
+ELRS::ELRS(const uint8_t portNumber, HALSITL::SITL_State_Common *sitl_state) :
+    // Mirror typical ELRS UART buffer sizes
+    SerialDevice::SerialDevice(64, 128),
+    target_address("127.0.0.1"),
+    target_port(5761 + portNumber),
+    // Mirror MAVLink buffer sizes
+    mavlinkInputBuffer(2048),
+    mavlinkOutputBuffer(2048),
+    // Typical setup is about 500 B /s
+    input_data_rate(500),
+    output_data_rate(500),
+    // 255 is typically used by the GCS, for RC override to work in ArduPilot `SYSID_MYGCS` must be set to this value (255 is the default)
+    this_system_id(255),
+    // Strictly this is not a valid source component ID
+    this_component_id(MAV_COMPONENT::MAV_COMP_ID_ALL)
+{
+
+    // Setup TCP server
+    listener.reuseaddress();
+    listener.bind(target_address, target_port);
+    listener.listen(1);
+    listener.set_blocking(false);
+
+}
+
+void ELRS::update()
+{
+    // Connect to incoming TCP
+    if (sock == nullptr) {
+        sock = listener.accept(0);
+        if (sock != nullptr) {
+            sock->set_blocking(false);
+            sock->reuseaddress();
+            ::printf("ELRS connected to %s:%u\n", target_address, (unsigned)target_port);
+        }
+    }
+    if (sock == nullptr) {
+        return;
+    }
+
+    // Read from AP into radio
+    const uint32_t input_space = mavlinkInputBuffer.space();
+    if (input_space > 0) {
+        uint8_t buf[input_space];
+        ssize_t len = read_from_autopilot((char*)buf, input_space);
+        mavlinkInputBuffer.write(buf, len);
+    }
+
+    // Send from radio to GCS
+    const uint32_t send_bytes = input_limit.max_bytes(input_data_rate);
+    if (send_bytes > 0) {
+        uint8_t buf[send_bytes];
+        const uint32_t len = mavlinkInputBuffer.read(buf, send_bytes);
+        if (len > 0) {
+            sock->send(buf, len);
+        }
+    }
+
+    // Incoming data from GCS to radio
+    const uint32_t receive_bytes = output_limit.max_bytes(output_data_rate);
+    if (receive_bytes > 0) {
+        uint8_t buf[receive_bytes];
+        const ssize_t len = sock->recv(buf, receive_bytes, 1);
+        if (len > 0) {
+            mavlinkOutputBuffer.write(buf, len);
+        } else if (len == 0) {
+            // EOF, go back to waiting for a new connection
+            delete sock;
+            sock = nullptr;
+        }
+    }
+
+    // Write from radio to AP
+    sendQueuedData();
+}
+
+// Function to behave like MAVLink libs `mavlink_parse_char` but use local buffer
+uint8_t ELRS::mavlink_parse_char_helper(uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
+{
+    uint8_t msg_received = mavlink_frame_char_buffer(&mavlink.rxmsg, &mavlink.status, c, r_message, r_mavlink_status);
+    if ((msg_received == MAVLINK_FRAMING_BAD_CRC) || (msg_received == MAVLINK_FRAMING_BAD_SIGNATURE)) {
+        return 0;
+    }
+    return msg_received;
+}
+
+// Send incoming data to AP, this is a re-implementation of the ELRS function found here:
+// https://github.com/ExpressLRS/ExpressLRS/blob/0d31863f34ca16a036e94a9c2a56038ae56c7f9e/src/src/rx-serial/SerialMavlink.cpp#L78
+void ELRS::sendQueuedData()
+{
+
+    // Send radio messages at 100Hz
+    const uint32_t now = AP_HAL::millis();
+    if ((now - lastSentFlowCtrl) > 10) {
+        lastSentFlowCtrl = now; 
+
+        // Space remaining as a percentage.
+        const uint8_t percentage_remaining = (mavlinkInputBuffer.space() * 100) / mavlinkInputBuffer.get_size();
+
+        // Populate radio status packet
+        const mavlink_radio_status_t radio_status {
+            rxerrors: 0,
+            fixed: 0,
+            rssi: UINT8_MAX, // Unknown
+            remrssi: UINT8_MAX, // Unknown
+            txbuf: percentage_remaining,
+            noise: UINT8_MAX, // Unknown
+            remnoise: UINT8_MAX, // Unknown
+        };
+
+        uint8_t buf[MAVLINK_MSG_ID_RADIO_STATUS_LEN + MAVLINK_NUM_NON_PAYLOAD_BYTES];
+        mavlink_message_t msg;
+        mavlink_msg_radio_status_encode(this_system_id, this_component_id, &msg, &radio_status);
+        uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
+        write_to_autopilot((char*)buf, len);
+    }
+
+    // Read one byte at a time until were done
+    while (true) {
+        uint8_t c;
+        if (!mavlinkOutputBuffer.read_byte(&c)) {
+            break;
+        }
+
+        mavlink_message_t msg;
+        mavlink_status_t status;
+
+        // Try parse a mavlink message
+        if (mavlink_parse_char_helper(c, &msg, &status)) {
+            // Message decoded successfully
+
+            // Forward message to the UART
+            uint8_t buf[MAVLINK_MAX_PACKET_LEN];
+            uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
+            uint16_t written = write_to_autopilot((char*)buf, len);
+            if ((written != uint16_t(-1)) && (len != written)) {
+                ::fprintf(stderr, "Failed to write full msg, wanted %u achieved %u (msg id: %u)\n", len, written, msg.msgid);
+            }
+        }
+    }
+
+}
+
+#endif // CONFIG_HAL_BOARD == HAL_BOARD_SITL

libraries/SITL/SIM_ELRS.h

@@ -0,0 +1,51 @@
+#pragma once
+
+#include <SITL/SITL.h>
+#include "SIM_SerialDevice.h"
+#include <AP_HAL/utility/DataRateLimit.h>
+#include <AP_HAL/utility/Socket_native.h>
+
+namespace SITL {
+
+class ELRS : public SerialDevice {
+public:
+    ELRS(const uint8_t portNumber, HALSITL::SITL_State_Common *sitl_state);
+
+    uint32_t device_baud() const override { return 460800; }
+
+    void update();
+
+private:
+    void sendQueuedData();
+
+    struct {
+        mavlink_message_t rxmsg;
+        mavlink_status_t status;
+    } mavlink;
+
+    uint8_t mavlink_parse_char_helper(uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status);
+
+    ByteBuffer mavlinkInputBuffer;
+    ByteBuffer mavlinkOutputBuffer;
+
+    DataRateLimit input_limit;
+    DataRateLimit output_limit;
+
+    uint32_t lastSentFlowCtrl;
+
+    const uint8_t this_system_id;
+    const uint8_t this_component_id;
+
+    // Air data rate limits in bytes per second
+    const float input_data_rate;
+    const float output_data_rate;
+
+    // Sockets for communicating with GCS
+    SocketAPM_native listener {false};
+    SocketAPM_native *sock = nullptr;
+    const char *target_address;
+    const uint16_t target_port;
+
+};
+
+}