The General USB Process
Frames in More Detail
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| Token |
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| Data |
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| Handshake |
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Control, Interrupt,
Bulk,
Isochronous
– General Concepts
Transfer 1 |
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| Transfer 2 |
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| Transfer N |
| Transfer 1 |
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Transaction | Transaction 1 | Transaction 2 | Transaction 3 |
| Transaction 1 |
| Transaction |
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Start of Frame | Packet 1 | Packet 2 | Packet 3 | Packet 1 | Packet 2 | Packet 3 | Packet 1 | Packet 2 | Packet 3 | Unused | Packet 1 | Packet 2 | Packet 3 | Unused | Start of Frame | … |
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1 Ms Frame
Software
Each frame begins with a Start of Frame packet followed by the hosts transactions to device endpoints for data transfer.
The host schedules transactions within 1mS frames for low and full speed.
Transfers may span multiple frames.
The host may schedule transactions anywhere in the frame, but they must complete within the frame.
