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Initial version of MAVlink output AIRDOS03 variant.
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‎fw/AIRDOS03_MAVLink/README.md‎

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# AIRDOS firwware suitable to connection MAVlink-based UAV platform
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# AIRDOS03 MAVLink Firmware
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The firmware outputs [MAVLink messages](https://en.wikipedia.org/wiki/MAVLink) suitable to interfacing to [TF-ATMON](https://docs.thunderfly.cz/instruments/TF-ATMON) system.
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MAVLink tunnel-based firmware for AIRDOS03B on TFUNIPAYLOAD01 (ATmega1284P, 8 MHz). Functionally equivalent to `fw/AIRDOS03_USTDFF` but transmits data as binary MAVLink TUNNEL packets instead of ASCII text, suitable for integration with [TF-ATMON](https://docs.thunderfly.cz/instruments/TF-ATMON) and PX4/ArduPilot autopilots.
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### Loading compiled binaries to MCU
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## Build and upload
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```
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source ~/.venv/bin/activate
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pio run -e TFUNIPAYLOAD01_uart -t upload
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```
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Using avrdude directly:
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```
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avrdude -v -patmega1284p -carduino -P/dev/ttyUSB0 -b57600 -D -Uflash:w:firmware.hex:i
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```
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## Decode to text format
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```
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pip install pymavlink
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python tools/mavlink_to_airdos.py --port /dev/ttyUSB0 --baud 115200
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python tools/mavlink_to_airdos.py --stdin < capture.bin
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```
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Output is AIRDOS04-compatible ASCII format (same as `fw/AIRDOS03_USTDFF`).
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## MAVLink Packet Protocol
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All packets use TUNNEL message (`payload_type = 4`, sensor ID for AIRDOS03B).
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The message sub-type is encoded as **byte 0** of the 128-byte payload.
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```cpp
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SendTunnelData(buf, len, 4, 1, 1); // same payload_type for all AIRDOS03B messages
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```
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All multi-byte integers are **little-endian**.
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### Message sub-types
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| Byte 0 | Name | Corresponds to | Payload size |
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|--------|-----------------|-------------------|--------------|
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| 0x01 | AIRDOS_STARTUP | `$DOS` + `$ADC` | 29 B |
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| 0x02 | AIRDOS_TIMESYNC | `$TIME` | 18 B |
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| 0x03 | AIRDOS_START | `$START` | 5 B |
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| 0x04 | AIRDOS_STOP | `$STOP` header | 14 B |
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| 0x05 | AIRDOS_HIST_LO | histogram[0..31] | 69 B |
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| 0x06 | AIRDOS_HIST_HI | histogram[32..63] | 67 B |
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| 0x07 | AIRDOS_EVENTS | `$E` events | ≤121 B |
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| 0x08 | AIRDOS_ENV | `$ENV` | 17 B |
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---
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### 0x01 — STARTUP (29 bytes)
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Sent once at startup. Provides device identification (`$DOS`, `$ADC`).
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```
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Offset Size Field
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0 1 sub_type = 0x01
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1 1 threshold // THRESHOLD constant (64)
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2 2 max_events // MAX_EVENTS constant (300)
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4 16 serial_number // raw bytes from EEPROM 0x5B offset 0x0800
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20 1 adc_conf1 // from EEPROM 0x53 offset 0x0000
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21 1 adc_conf2 // from EEPROM 0x53 offset 0x0001
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22 1 fw_major // MAJOR version
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23 1 fw_minor // MINOR version
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24 4 reserved // zero
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```
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Python: `struct.unpack_from('<BBH16sBBBB4s', payload)`
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---
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### 0x02 — TIMESYNC (18 bytes)
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Sent on first GNSS fix and on re-sync after fix loss (`$TIME`).
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```
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Offset Size Field
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0 1 sub_type = 0x02
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1 1 gnss_synced // 1 = valid GNSS fix, 0 = not synced
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2 4 rtc_seconds // 1PPS-derived seconds counter
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6 4 gnss_sync_unix // Unix time from last valid $GNRMC
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10 4 current_unix // gnss_sync_unix + (rtc_seconds - sync_rtc_seconds)
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14 4 sync_age // seconds since last GNSS fix
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```
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Python: `struct.unpack_from('<BB4I', payload)`
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---
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### 0x03 — START (5 bytes)
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Sent at start of each 10 s integration window (`$START`).
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```
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Offset Size Field
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0 1 sub_type = 0x03
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1 2 count // measurement cycle index
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3 2 start_systime // TCNT1 at start of window (128 µs/tick)
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```
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Python: `struct.unpack_from('<BHH', payload)`
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---
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### 0x04 — STOP (14 bytes)
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Sent after events, before histogram packets (`$STOP` header fields).
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```
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Offset Size Field
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0 1 sub_type = 0x04
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1 2 count // same cycle index as START
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3 4 tm // Unix time at end of window (0 if not synced)
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7 1 tm_s100 // hundredths of second (0–99)
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8 2 stop_systime // TCNT1 at end of window
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10 2 events_total // total events_counter (may exceed MAX_EVENTS)
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12 2 events_sent // min(events_total, MAX_EVENTS)
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```
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Python: `struct.unpack_from('<B H I B H H H', payload)` (no padding)
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---
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### 0x05 — HIST_LO (69 bytes) and 0x06 — HIST_HI (67 bytes)
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64-channel uint16 histogram split across two packets (lossless). Together they form
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the histogram fields of `$STOP`.
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```
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HIST_LO (0x05): HIST_HI (0x06):
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Offset Size Field Offset Size Field
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0 1 sub_type = 0x05 0 1 sub_type = 0x06
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1 2 count 1 2 count
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3 64 hist[0..31] 3 64 hist[32..63]
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(32 × uint16) (32 × uint16)
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```
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Python: `struct.unpack_from('<BH32H', payload)`
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---
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### 0x07 — EVENTS (≤121 bytes, chunked)
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Up to 29 events per packet. Sent only if `events_sent > 0`.
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Multiple packets with `chunk_index` 0 … `chunk_total − 1`. Each event → one `$E` line.
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```
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Offset Size Field
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0 1 sub_type = 0x07
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1 2 count // cycle index
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3 1 chunk_index // 0-based
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4 1 chunk_total // total chunks for this cycle
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5 1 events_in_chunk // events in this packet (1–29)
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6 3 reserved
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9 events_in_chunk × 4:
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uint16 event_time // TCNT1 (128 µs/tick)
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uint16 event_channel // ADC value ≥ THRESHOLD (64)
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```
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Max: 9 + 29 × 4 = 125 B. For 300 events: ceil(300/29) = 11 packets.
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Python header: `struct.unpack_from('<BHBBBxxx', payload[:9])`
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Python events: `struct.unpack_from(f'<{2*n}H', payload[9:9+n*4])` — pairs (time, channel)
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---
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### 0x08 — ENV (17 bytes)
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Sent at startup and every 30 s (`$ENV`).
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```
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Offset Size Field
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0 1 sub_type = 0x08
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1 2 count // measurement cycle index
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3 4 tm // Unix time (0 if not synced)
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7 1 tm_s100 // hundredths of second
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8 1 reserved
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9 4 temperature // float32, °C (IEEE 754 single, little-endian)
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13 4 humidity // float32, % RH
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```
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Python: `struct.unpack_from('<BHIBxff', payload)`
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---
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## Emission sequence
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```
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At setup():
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STARTUP (0x01)
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ENV (0x08) ← initial sensor reading
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Every 10 s:
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START (0x03)
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EVENTS (0x07) × N chunks (omitted if events_sent == 0)
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STOP (0x04)
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HIST_LO (0x05)
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HIST_HI (0x06)
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Every 30 s (in addition to measurement cycle):
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ENV (0x08)
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On GNSS fix or re-sync after fix loss:
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TIMESYNC (0x02)
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```
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---
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#### Avrdude
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## Decoder output format
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In case of using the avrdude and mightyCore bootloader we should use following command:
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`tools/mavlink_to_airdos.py` reconstructs AIRDOS04-compatible text:
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```
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avrdude -v -patmega1284p -carduino -P/dev/ttyUSB0 -b57600 -D -Uflash:w:/tmp/arduino_build_743311/LABDOS.ino.hex:i
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$DOS,AIRDOS03B,<major>.<minor>,0,unknown,MAVLink,<sn_hex_32chars>
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$ADC,USTSIPIN03C,<sn_hex_32chars>,<conf1hex><conf2hex>
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$TIME,<rtc_seconds>,<gnss_sync_unix>,<current_unix>,<sync_age>,<YYYY-MM-DD HH:MM:SS>
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$START,<count>,<start_systime>
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$E,<event_time>,<event_channel>
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$STOP,<count>,<tm>.<tm_s100>,<stop_systime>,<events_total>,<hist_0>,...,<hist_63>
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$ENV,<count>,<tm>.<tm_s100>,<tempC>,<humidity>
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```

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