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updated to next generation of enhanced protocol

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john30
2019-11-26 20:57:20 +01:00
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## Transfer speed
In order to compensate potential overhead of transfer encoding, the transfer speed is set to 9600 Baud with 8 bits, no parity, and 1 stop bit.
## Protocol ## Protocol
Data bytes with a value below 0x80 can be transferred as is.
Every communication in either direction is prefixed with at most one byte indicating the kind of action/result. Data bytes with value above or equal to 0x80 are split up into two bytes, each one with the highest bit set to 1.
The second bit indicates whether it is the first or second byte of a split transfer. This way protocol errors can easily be detected.
The bits in the two bytes look like this:
### from ebusd to device ```
* initialization (after connect) first second
`<INIT>` 76543210 76543210
This is not yet implemented in ebusd and supposed to be enhanced by another byte requesting certain features. 11ccccdd 10dddddd
* send request ```
`<SEND> <symbol>` 4 bits in `c` are used for indicating a special purpose and is set to one of the command request/response symbols as stated below.
Requests the specified symbol to be sent to the eBUS. 8 bits in `d` are the data byte to be transferred (might also be unused).
### Command request/response symbols
#### from ebusd to device
* initialization request
`<INIT> <features>`
Requests an initialization of the device and requests special features in the data byte (tbd).
* send data request
`<SEND> <data>`
Requests the specified data byte in `d` to be sent to the eBUS.
For data byte values <0x80, the short form without the `<SEND>` prefix is allowed as well.
* arbitration start request * arbitration start request
`<START> <master address>` `<START> <master>`
Requests the start of the arbitration process with the specified master address after the next received `<SYN>` symbol. Requests the start of the arbitration process after the next received `<SYN>` symbol with the specified master address in `d`.
### from device to ebusd #### from device to ebusd
* initialization (after re-connect) * initialization response
`<RESETTED>` `<RESETTED> <features>`
Indicates a reboot or an initial ebusd connection on the device. Indicates a reboot or an initial ebusd connection on the device and is expected to be returned after an `<INIT`> request.
This is actually desired to be enhanced by another byte in future indicating availability of certain features (like full message sending instead of arbitration onnly). The data byte `d` indicates availability of certain features (like full message sending instead of arbitration only, tbd).
* symbol received from eBUS * receive data notification
`<RECEIVED> <symbol>` `<RECEIVED> <data>`
Indicates that the specified symbol was received from the eBUS. Indicates that the specified data byte in `d` was received from the eBUS.
* arbitration start succeeded For data byte values <0x80, the short form without the `<RECEIVED>` prefix is allowed as well.
`<STARTED>` * arbitration start succeeded
Indicates that the last arbitration request was successful (arbitration was won). `<STARTED> <info>`
Indicates the the last arbitration request succeeded (arbitration was won).
The data byte in `d` may contain additional information (tbd).
* arbitration start failed * arbitration start failed
`<FAILED>` `<FAILED> <master>`
Indicates that the last arbitration request failed (arbitration was lost or sending failed). Indicates that the last arbitration request failed (arbitration was lost or sending failed).
The data byte in `d` contains the address of the master that won the arbitration.
## Symbols ## Symbols
These are the predefined symbols as used above. These are the predefined symbols as used above.
### Generic ### Bus symbols
* SYN 0xAA * SYN 0xAA
### From ebusd to device ### Command request symbols (from ebusd to device)
* INIT 0x00 * INIT 0x0
* SEND 0x01 * SEND 0x1
* START 0x02 * START 0x2
### From device to ebusd
* RESETTED 0x00
* RECEIVED 0x01
* STARTED 0x02
* FAILED 0x82
### Command response symbols (from device to ebusd)
* RESETTED 0x0
* RECEIVED 0x1
* STARTED 0x2
* FAILED 0xa