AP_RCProtocol: added ibus RX support to recieve channel data from ibus transmitters.

libraries/AP_RCProtocol/AP_RCProtocol.cpp

@@ -18,6 +18,7 @@
 #include "AP_RCProtocol.h"
 #include "AP_RCProtocol_PPMSum.h"
 #include "AP_RCProtocol_DSM.h"
+#include "AP_RCProtocol_IBUS.h"
 #include "AP_RCProtocol_SBUS.h"
 #include "AP_RCProtocol_SUMD.h"
 #include "AP_RCProtocol_SRXL.h"
@@ -29,6 +30,7 @@ AP_RCProtocol *AP_RCProtocol::_singleton;
 void AP_RCProtocol::init()
 {
     backend[AP_RCProtocol::PPM] = new AP_RCProtocol_PPMSum(*this);
+    backend[AP_RCProtocol::IBUS] = new AP_RCProtocol_IBUS(*this);
     backend[AP_RCProtocol::SBUS] = new AP_RCProtocol_SBUS(*this, true);
     backend[AP_RCProtocol::SBUS_NI] = new AP_RCProtocol_SBUS(*this, false);
     backend[AP_RCProtocol::DSM] = new AP_RCProtocol_DSM(*this);
@@ -205,6 +207,8 @@ const char *AP_RCProtocol::protocol_name_from_protocol(rcprotocol_t protocol)
     switch (protocol) {
     case PPM:
         return "PPM";
+    case IBUS:
+        return "IBUS";
     case SBUS:
     case SBUS_NI:
         return "SBUS";

libraries/AP_RCProtocol/AP_RCProtocol.h

@@ -32,6 +32,7 @@ public:
 
     enum rcprotocol_t {
         PPM = 0,
+        IBUS,
         SBUS,
         SBUS_NI,
         DSM,

libraries/AP_RCProtocol/AP_RCProtocol_IBUS.cpp

@@ -0,0 +1,106 @@
+/*
+ * This file 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 file 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 <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "AP_RCProtocol_IBUS.h"
+
+// constructor
+AP_RCProtocol_IBUS::AP_RCProtocol_IBUS(AP_RCProtocol &_frontend) :
+    AP_RCProtocol_Backend(_frontend)
+{}
+
+// decode a full IBUS frame
+bool AP_RCProtocol_IBUS::ibus_decode(const uint8_t frame[IBUS_FRAME_SIZE], uint16_t *values, bool *ibus_failsafe)
+{
+    uint32_t chksum = 96;
+
+    /* check frame boundary markers to avoid out-of-sync cases */
+    if ((frame[0] != 0x20) || (frame[1] != 0x40)) {
+        return false;
+    }
+
+    /* use the decoder matrix to extract channel data */
+    for (uint8_t channel = 0, pick=2; channel < IBUS_INPUT_CHANNELS; channel++, pick+=2) {
+        values[channel]=frame[pick]|(frame[pick+1] & 0x0F)<<8;
+        chksum+=frame[pick]+frame[pick+1];
+    }
+
+    chksum += frame[IBUS_FRAME_SIZE-2]|frame[IBUS_FRAME_SIZE-1]<<8;
+
+    if (chksum!=0xFFFF) {
+        return false;
+    }
+
+    if ((frame[3]&0xF0) || (frame[9]&0xF0)) {
+        *ibus_failsafe = true;
+    } else {
+        *ibus_failsafe = false;
+    }
+
+    return true;
+}
+
+
+/*
+  process an IBUS input pulse of the given width
+ */
+void AP_RCProtocol_IBUS::process_pulse(uint32_t w0, uint32_t w1)
+{
+    uint8_t b;
+    if (ss.process_pulse(w0, w1, b)) {
+        _process_byte(ss.get_byte_timestamp_us(), b);
+    }
+}
+
+// support byte input
+void AP_RCProtocol_IBUS::_process_byte(uint32_t timestamp_us, uint8_t b)
+{
+    const bool have_frame_gap = (timestamp_us - byte_input.last_byte_us >= 2000U);
+    byte_input.last_byte_us = timestamp_us;
+
+    if (have_frame_gap) {
+        // if we have a frame gap then this must be the start of a new
+        // frame
+        byte_input.ofs = 0;
+    }
+    if (b != 0x20 && byte_input.ofs == 0) {
+        // definately not IBUS, missing header byte
+        return;
+    }
+    if (byte_input.ofs == 0 && !have_frame_gap) {
+        // must have a frame gap before the start of a new IBUS frame
+        return;
+    }
+
+    byte_input.buf[byte_input.ofs++] = b;
+
+    if (byte_input.ofs == sizeof(byte_input.buf)) {
+        uint16_t values[IBUS_INPUT_CHANNELS];
+        bool ibus_failsafe = false;
+        if (ibus_decode(byte_input.buf, values, &ibus_failsafe)) {
+            add_input(IBUS_INPUT_CHANNELS, values, ibus_failsafe);
+        }
+        byte_input.ofs = 0;
+    }
+}
+
+// support byte input
+void AP_RCProtocol_IBUS::process_byte(uint8_t b, uint32_t baudrate)
+{
+    if (baudrate != 115200) {
+        return;
+    }
+    _process_byte(AP_HAL::micros(), b);
+}

libraries/AP_RCProtocol/AP_RCProtocol_IBUS.h

@@ -0,0 +1,43 @@
+/*
+ * This file 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 file 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 <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#pragma once
+
+#define IBUS_FRAME_SIZE		32
+#define IBUS_INPUT_CHANNELS	14
+
+#include "AP_RCProtocol.h"
+#include "SoftSerial.h"
+
+class AP_RCProtocol_IBUS : public AP_RCProtocol_Backend
+{
+public:
+    AP_RCProtocol_IBUS(AP_RCProtocol &_frontend);
+    void process_pulse(uint32_t width_s0, uint32_t width_s1) override;
+    void process_byte(uint8_t byte, uint32_t baudrate) override;
+private:
+    void _process_byte(uint32_t timestamp_us, uint8_t byte);
+    bool ibus_decode(const uint8_t frame[IBUS_FRAME_SIZE], uint16_t *values, bool *ibus_failsafe);
+
+    SoftSerial ss{115200, SoftSerial::SERIAL_CONFIG_8N1};
+    uint32_t saved_width;
+
+    struct {
+        uint8_t buf[IBUS_FRAME_SIZE];
+        uint8_t ofs;
+        uint32_t last_byte_us;
+    } byte_input;
+};

libraries/AP_RCProtocol/examples/RCProtocolTest/RCProtocolTest.cpp

@@ -210,9 +210,13 @@ void loop()
     const uint16_t sumd_output[] = {1597, 1076, 1514, 1514, 1100, 1100, 1500, 1500};
     const uint16_t sumd_output2[] = {1516, 1500, 1100, 1500, 1900, 1900, 1900, 1900, 1900, 1900, 1900, 1900};
     
+    const uint8_t ibus_bytes[] = {0x20, 0x40, 0xdc, 0x05, 0xdc, 0x05, 0xe8, 0x03, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0xdc, 0x05, 0x47, 0xf3};
+    const uint16_t ibus_output[] = {1500, 1500, 1000, 1500, 1500, 1500, 1500, 1500, 1500, 1500, 1500, 1500, 1500, 1500};
+
     test_protocol("SRXL", 115200, srxl_bytes, sizeof(srxl_bytes), srxl_output, ARRAY_SIZE(srxl_output), 1);
     test_protocol("SUMD", 115200, sumd_bytes, sizeof(sumd_bytes), sumd_output, ARRAY_SIZE(sumd_output), 1);
     test_protocol("SUMD", 115200, sumd_bytes2, sizeof(sumd_bytes2), sumd_output2, ARRAY_SIZE(sumd_output2), 1);
+    test_protocol("IBUS", 115200, ibus_bytes, sizeof(ibus_bytes), ibus_output, ARRAY_SIZE(ibus_output), 1);
 
     // SBUS needs 3 repeats to pass the RCProtocol 3 frames test
     test_protocol("SBUS", 100000, sbus_bytes, sizeof(sbus_bytes), sbus_output, ARRAY_SIZE(sbus_output), 3);