108 lines
5.7 KiB
Markdown
108 lines
5.7 KiB
Markdown
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# FemtoTCP
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## Stack architecture
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- No dynamic allocation (pre-allocated sockets and buffers)
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- Four-steps main loop function
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- Callback-based socket interface (allows implementing blocking BSD calls)
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## Data structures
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* Two types of circular buffers (fixed size):
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- "fifo" : contains entire frames, including a descriptor.
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- "queue" : contains pure data, indexed by byte. Used for TCP receive buffer
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only.
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* One binary heap for timers
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### FemtoTCP fifo
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```
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+---------------------------------------------------------------------------------------------------------------------------+
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| +-----+---+----+-----+------------------+-----+---+----+-----+------------------+ |
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| | De | E | IP | TCP | Payload | De | E | IP | TCP | Payload | |
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| | sc | T | | | | sc | T | | | | |
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|* FREE SPACE * | ri | H | | | | ri | H | | | | * FREE SPACE* |
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| | pt | | | | | pt | | | | | |
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| | or | | | | | or | | | | | |
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| +-----+---+----+-----+------------------+-----+---+----+-----+------------------+ |
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+---------------------------------------------------------------------------------------------------------------------------+
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^ ^
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|Tail Head|
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```
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### FemtoTCP queue
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```
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+--------------+--------------------------------------------+---------------------------------------------------------------+
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| |*------------------------------------------*| |
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|* FREE SPACE *|| DATA PAYLOAD || * FREE SPACE * |
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| |*------------------------------------------*| |
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+--------------+--------------------------------------------+---------------------------------------------------------------+
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^ ^
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|Tail Head|
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```
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## Sockets
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### TCP socket
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```
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+-------------+
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|Main loop TX |
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+-------------+
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^
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+----------------------------------+ |
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| | +------+
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| TCP Socket | |
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| +-----------------------+
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| +---------------+ | |
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>DATA OUT==>>|socket send() |-->| TX buffer (fifo) |
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| +---------------+ | |
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| +-----------------------+
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| +-----------------------+
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| +-------------+ | |
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<DATA IN<<====|socket recv()|<---| RX buffer (queue) |
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| +-------------+ | |
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| +-----------------------+
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+----------------------------------+ ^
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+--------------+
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| tcp_recv() |
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+--------------+
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```
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