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- A pair of Bulk IN and OUT endpoints.
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Table - CDC EEM Subclass Endpoints Usage describes the usage of the different endpoints:
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| Endpoint | Direction | Usage |
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| Bulk In | Device-to-host | Send Ethernet frames and commands to host. |
| | Bulk OUT | Host-to-device | Receive Ethernet frames and commands from host. |
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CDC EEM Messages
CDC EEM defines a header that is prepended to each message sent to / received from the host. The CDC EEM header has a size of two bytes. A USB transfer on the Bulk endpoints can contain multiple EEM messages. An EEM message can also span on multiple USB transfers.
Table - CDC EEM Message Format describes the content of a CDC EEM message.
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| Bytes | 0..1 | 2..N |
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| Content | Header | Payload (optional) |
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Table - CDC EEM Header Format describes the content of a CDC EEM header.
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| Bit | 15 | 14 .. 0 |
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| Content | bmType | Depends on bmType value |
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- bmType represents the message type, either a regular Ethernet frame or a CDC EEM specific command.
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| Bit | 15 | 14 | 13 .. 0 |
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| Content | bmType (0) | bmCRC | Length of Ethernet frame |
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- bmCRC indicates if the CRC was calculated on the Ethernet frame. If not, CRC is set to 0xDEADBEEF.
Table - CDC EEM Command Header Format describes the content of a CDC EEM command message header. Note that the EEM commands provide USB local link management. This management is opaque to the network stack. | Anchor |
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| Bit | 15 | 14 | 13 .. 11 | 10 .. 0 |
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| Content | bmType (1) | bmReserved (0) | bmEEMCmd | bmEEMCmdParam |
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- bmEEMCmd represents the command code to execute.
- bmEEMCmdParam contains command data. Fomat depends on the bmEEMCmd.
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