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+/**
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+
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+ @page shellmatta_transport_layer Shellmatta Transport Layer
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+
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+ To be able to use the shellmatta directly on an unsecured interface like
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+ raw UART a simple connectionless transport layer has been implemented.
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+
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+ The transport layer is optional and can be removed during compile time as
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+ well as deactivated during runtime.
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+ The transport layer intends to be used in machine to machine interfaces.
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+
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+ @warning As the transport layer is connectionless there is no way to
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+ determine wether a packet is received properly.
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+ To check if all packets have been received by the shellmatta
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+ the sequence counters included in any packet can be used.
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+
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+ @section shellmatta_transport_layer_sequence Basic sequence
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+
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+ @startuml
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+ loop until command is sent
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+ Host -> Shellmatta: send packet
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+ Shellmatta -> Shellmatta: validate packet
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+ end
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+
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+ loop until response is sent
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+ Shellmatta -> Host: send return packet
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+ Host -> Host: validate packet
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+ end
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+ @enduml
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+
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+
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+ @section shellmatta_transport_layer_protocol Protocol
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+
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+
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+ | Offset | Length | Description |
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+ |--------|----------|---------------------------------------------|
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+ | 0 | 1 | Start of header (\SOH) |
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+ | 1 | 1 | Protocol version |
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+ | 2 | 1 | Packet type |
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+ | 3 | 1 | Payload Length |
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+ | 4 | 1 | Source |
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+ | 5 | 1 | Destination |
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+ | 6 | 1 | Sequence counter host to shellmatta |
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+ | 7 | 1 | Sequence counter shellmatta to host |
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+ | 8 | 4 | CRC32 of header + payload without CRC32 |
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+ | 12 | 0 .. 255 | Payload |
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+
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+
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+ @subsection shellmatta_transport_layer_protocol_packet_Types Packet types
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+
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+ The type codes are divided into request and respond codes using the MSB.
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+ The MSB indicates a response.
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+
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+ | type | Description | Payload length | Payload |
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+ |------|--------------------------------|----------------|------------------------|
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+ | 0x00 | Plain Data | 0 .. 255 | User data |
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+ | 0x01 | Request Sequence counters | 0 | - |
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+ | 0x81 | Respond Sequence counters | 0 | - |
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+ | 0x02 | Request and set max buffersize | 1 | Hosts buffersize |
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+ | 0x82 | Respond max buffersize | 1 | Shellmattas buffersize |
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+ | 0x03 | Search device by unique ID | 32 | UUID Range 2x 16 byte |
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+ | 0x83 | Respond to search | 16 | UUID of Shellmatta |
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+ | 0x04 | Set address | 16 | UUID of Shellmatta |
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+ | 0x84 | Respond to set address | 16 | UUID of Shellmatta |
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+
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+
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+
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+ @section shellmatta_transport_layer_sequence_counters Sequence counters
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+
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+ The sequence counters are included in the header of every packet to enable
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+ the host to check for any dropped packets.
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+ This is a quite nasty workaround as the host has no chance to determine
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+ which packet has dropped - but better than nothing.
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+
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+ If no response is received from the shellmatta the sequence counters can be
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+ requested explicitly.
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+
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+ The sequence counter host to shellmatta will increment on every successfully
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+ received packet.
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+
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+ The sequence counter shellmatta to host will increment on every packet the
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+ shellmatta sends to the host.
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+
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+
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+ @section shellmatta_transport_layer_buffersize Buffer sizes
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+
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+
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+ @section shellmatta_transport_layer_addressing Addressing and Search
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+
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+
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+ @section shellmatta_transport_layer_crc CRC calculation
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+
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+
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+ @section shellmatta_transport_layer_control Controlling the transport layer
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+
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+
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+*/
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