From 9c0e35388edde70ffd74ddcc40beef86e8594ff8 Mon Sep 17 00:00:00 2001
From: Andrew J Spence <aspence@temple.edu>
Date: Thu, 26 Mar 2026 09:19:33 -0400
Subject: [PATCH] First commit adding airspeed pitot sensor telemetry alone.
 Worked and very quickly bench tested. Built on Mac OS Tahoe on M2 Pro. Tested
 on Radiomaster NEXUS-XR target with Matek 4525 Airspeed sensor on I2C on
 connector C. Connection to INAV configurator 9.0.2 works and appears normal.
 After enabling sensor and confirming it shows up in sensors on INAV
 configurator, was able to see in Discover New Telemetry on EdgeTX 2.11.3 on a
 Radiomaster TX16S Mark 2. GPS still working. Needs further testing including
 flight. Update rate is very slow - at 250Hz link and 1:64 telemetry, get one
 ASpd telemetry update every 6 seconds or so. Could mess with INAV telemetry
 scheduling. Using telemetry index 0x0A as is ELRS standard.

---
 src/main/rx/crsf.h        |  2 ++
 src/main/telemetry/crsf.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/src/main/rx/crsf.h b/src/main/rx/crsf.h
index 8d84d52b8e5..07c256fea2e 100755
--- a/src/main/rx/crsf.h
+++ b/src/main/rx/crsf.h
@@ -46,6 +46,7 @@ enum {
     CRSF_FRAME_VARIO_SENSOR_PAYLOAD_SIZE = 2,
     CRSF_FRAME_BATTERY_SENSOR_PAYLOAD_SIZE = 8,
     CRSF_FRAME_BAROMETER_ALTITUDE_PAYLOAD_SIZE = 2,
+    CRSF_FRAME_AIRSPEED_PAYLOAD_SIZE = 2,
     CRSF_FRAME_LINK_STATISTICS_PAYLOAD_SIZE = 10,
     CRSF_FRAME_RC_CHANNELS_PAYLOAD_SIZE = 22, // 11 bits per channel * 16 channels = 22 bytes.
     CRSF_FRAME_ATTITUDE_PAYLOAD_SIZE = 6,
@@ -88,6 +89,7 @@ typedef enum {
     CRSF_FRAMETYPE_VARIO_SENSOR = 0x07,
     CRSF_FRAMETYPE_BATTERY_SENSOR = 0x08,
     CRSF_FRAMETYPE_BAROMETER_ALTITUDE = 0x09,
+    CRSF_FRAMETYPE_AIRSPEED = 0x0A,
     CRSF_FRAMETYPE_LINK_STATISTICS = 0x14,
     CRSF_FRAMETYPE_RC_CHANNELS_PACKED = 0x16,
     CRSF_FRAMETYPE_ATTITUDE = 0x1E,
diff --git a/src/main/telemetry/crsf.c b/src/main/telemetry/crsf.c
index d86822ada7a..522a893ddcf 100755
--- a/src/main/telemetry/crsf.c
+++ b/src/main/telemetry/crsf.c
@@ -57,6 +57,7 @@
 
 #include "sensors/battery.h"
 #include "sensors/sensors.h"
+#include "sensors/pitotmeter.h"
 
 #include "telemetry/crsf.h"
 #include "telemetry/telemetry.h"
@@ -296,6 +297,26 @@ static void crsfBarometerAltitude(sbuf_t *dst)
     crsfSerialize16(dst, altitude_packed);
 }
 
+/*
+0x0A Airspeed
+Payload:
+uint16_t    Airspeed ( km/h / 10 )
+*/
+static void crsfFrameAirspeed(sbuf_t *dst)
+{
+    sbufWriteU8(dst, CRSF_FRAME_AIRSPEED_PAYLOAD_SIZE + CRSF_FRAME_LENGTH_TYPE_CRC);
+    crsfSerialize8(dst, CRSF_FRAMETYPE_AIRSPEED);
+
+    // INAV airspeed is in cm/s
+    // CRSF airspeed wants 0.1 km/h
+    // 1 cm/s = 0.036 km/h = 0.36 (0.1 km/h)
+    // so airspeed_kmh_x10 = cm/s * 36 / 100, rounded
+    const float airspeedCms = getAirspeedEstimate();
+    const uint16_t airspeedKmhX10 = (uint16_t)(airspeedCms * 0.36f + 0.5f);
+
+    crsfSerialize16(dst, airspeedKmhX10);
+}
+
 typedef enum {
     CRSF_ACTIVE_ANTENNA1 = 0,
     CRSF_ACTIVE_ANTENNA2 = 1
@@ -465,6 +486,7 @@ typedef enum {
     CRSF_FRAME_GPS_INDEX,
     CRSF_FRAME_VARIO_SENSOR_INDEX,
     CRSF_FRAME_BAROMETER_ALTITUDE_INDEX,
+    CRSF_FRAME_AIRSPEED_INDEX,
     CRSF_SCHEDULE_COUNT_MAX
 } crsfFrameTypeIndex_e;
 
@@ -545,6 +567,11 @@ static void processCrsf(void)
         crsfFinalize(dst);
     }
 #endif
+    if (currentSchedule & BV(CRSF_FRAME_AIRSPEED_INDEX)) {
+        crsfInitializeFrame(dst);
+        crsfFrameAirspeed(dst);
+        crsfFinalize(dst);
+    }
     crsfScheduleIndex = (crsfScheduleIndex + 1) % crsfScheduleCount;
 }
 
@@ -583,6 +610,9 @@ void initCrsfTelemetry(void)
         crsfSchedule[index++] = BV(CRSF_FRAME_BAROMETER_ALTITUDE_INDEX);
     }
 #endif
+    if (sensors(SENSOR_PITOT)) {
+        crsfSchedule[index++] = BV(CRSF_FRAME_AIRSPEED_INDEX);
+    }
     crsfScheduleCount = (uint8_t)index;
 }
 
@@ -659,6 +689,9 @@ int getCrsfFrame(uint8_t *frame, crsfFrameType_e frameType)
     case CRSF_FRAMETYPE_VARIO_SENSOR:
         crsfFrameVarioSensor(sbuf);
         break;
+    case CRSF_FRAMETYPE_AIRSPEED:
+        crsfFrameAirspeed(sbuf);
+        break;
     }
     const int frameSize = crsfFinalizeBuf(sbuf, frame);
     return frameSize;