Software – General Concepts
The General USB Process
The Enumeration Process:What happens when a device is connected?
5.The available bandwidth is then divided into frames, and the host controls those frames which contain 1,500 bytes. Every millisecond a new frame begins. Within the frame, slots are reserved for isochronous and interrupt devices (up to 90%) so that they are guaranteed the bandwidth they need. Bulk and control transfers use whatever space is left.
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| TM |
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| Frame |
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Transfer 1 |
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| Transfer 2 |
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| Transfer 3 | ||||
Transaction | Transaction 1 | Transaction 2 | Transaction 3 | Transaction 1 | ||||||||
Start of Frame | Packet 1 | Packet 2 | Packet 3 | Packet 1 | Packet 2 | Packet 3 | Packet 1 | Packet 2 | Packet 3 | Packet 1 | Packet 2 | Packet 3 |
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| 1500 bytes / 1 Ms |
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