75 lines
2.1 KiB
Markdown
75 lines
2.1 KiB
Markdown
# Host Communication Protocol (HCP)
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Welcome to the documentation for the Host Communication Protocol (HCP).
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The first part covers the physical method of sending messages and the second part covers the
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specification of the different command flows.
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## FPC embedded stack and HCP
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The communication stack implemented on the embedded devices by FPC follows the following specification.
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**HCP embedded stack**
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#### Physical
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The physical layer have a fixed size buffer of 256 bytes.
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#### Link
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The link layer handles packet consistency.
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Each packet received is acknowledged on the link layer, if an error occurs no retransmission is done on this level, instead the error is propagated upwards.
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| Channel | Size | Payload | CRC |
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| :------: | :------: | :------: | :------:|
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| 2 bytes | 2 bytes | size bytes | 4 bytes
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All fields are using unsigned data types.
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#### Transport
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The transport layer handles packet segmentation.
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As the PHY MTU is 256 bytes the maximum payload per segment is 242 bytes.
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Errors are propagated upwards.
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|Size | Seq Nr | Seq Len | Payload |
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| :------: | :------: | :------: | :------:|
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|2 bytes | 2 bytes | 2 bytes | size bytes|
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All fields are using unsigned data types.
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#### Application
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The application layer is a optional security layer, the default implementation is clear text (unsecure).
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If a security solution is used it will be part of that products documentation.
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## HCP frame format
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#### Command
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The Commands define the general action that is going to be executed. However, each command can have several Arguments each with data attached.
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| CMD | Num Args | Payload |
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| :------: | :------: | :------: |
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| 2 bytes | 2 bytes | xx bytes |
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All fields are using unsigned data types.
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#### Argument
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The Argument is used as a complement to the command if it is needed and can contain arbitrary data.
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| ARG | Size | Data |
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| :------: | :------: | :------: |
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| 2 bytes | 2 bytes | size bytes |
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All fields are using unsigned data types.
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