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24 lines
1.3 KiB
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24 lines
1.3 KiB
Plaintext
---
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id: python-stream
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title: Meshtastic-python stream protocol
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sidebar_label: Stream Protocol
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---
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# Stream protocol
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Documentation on how out protobufs get encoded when placed onto any stream transport (i.e. TCP or serial, but not UDP or BLE)
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## Wire encoding
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When sending protobuf packets over serial or TCP each packet is preceded by uint32 sent in network byte order (big endian).
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The upper 16 bits must be 0x94C3. The lower 16 bits are packet length (this encoding gives room to eventually allow quite large packets).
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Implementations validate length against the maximum possible size of a BLE packet (our lowest common denominator) of 512 bytes. If the
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length provided is larger than that we assume the packet is corrupted and begin again looking for 0x4403 framing.
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The packets flowing towards the device are ToRadio protobufs, the packets flowing from the device are FromRadio protobufs.
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The 0x94C3 marker can be used as framing to (eventually) resync if packets are corrupted over the wire.
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Note: the 0x94C3 framing was chosen to prevent confusion with the 7 bit ascii character set. It also doesn't collide with any valid utf8 encoding. This makes it a bit easier to start a device outputting regular debug output on its serial port and then only after it has received a valid packet from the PC, turn off unencoded debug printing and switch to this
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packet encoding.
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