93 lines
1.6 KiB
Markdown
93 lines
1.6 KiB
Markdown
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# Host COM Rebuild
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## Goal
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Keep the COM layer small, explicit, and easy to teach.
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The COM layer should:
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- define packet types and payload structures
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- build full wire frames
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- parse full wire frames
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- parse typed packet payloads
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The COM layer should not:
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- enumerate devices
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- open ports
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- own handshake state
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- own UI state
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## Current file roles
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### `Com_Cdc.h`
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Owns the packet model:
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- packet types
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- fixed payload lengths
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- payload structs
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### `Com_CdcEncode.h/.cpp`
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Owns the write direction:
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- checksum
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- full frame build
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- typed payload encode
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### `Com_CdcDecode.h/.cpp`
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Owns the read direction:
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- full frame parse
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- stream extraction
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- typed payload decode
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## Completed nodes
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### Node 1: legacy frame encode baseline
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Already present before this step:
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- build full frame
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- build all typed packets
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### Node 2: typed packet decode completion
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Files updated in this step:
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- `KeyBorad/KeyBorad/COM/Com_CdcDecode.h`
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- `KeyBorad/KeyBorad/COM/Com_CdcDecode.cpp`
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Design notes:
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- keep decode logic flat and explicit
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- one helper for little-endian reads
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- one helper for type + length validation
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- one decode function per packet type
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Implemented behavior:
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- parse frame header and checksum
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- extract frames from a byte stream
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- decode:
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- `HelloReq`
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- `HelloRsp`
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- `Bitmap`
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- `FunctionKeyEvent`
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- `LedState`
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- `TimeSync`
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- `ThemeRgb`
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- `Ack`
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- `Error`
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## COM done criteria
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For the current project stage, COM is considered done when:
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1. every supported packet can be built
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2. every supported packet can be parsed
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3. stream extraction is stable
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4. higher layers no longer need to know byte offsets
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