Zedmon devices all share the same device and vendor ID:
Vendor ID 0x18d1 (Google, Inc.)
Device ID: 0xaf00
Zedmon exposes two USB interfaces. One is a CDC Serial interface that can be used to communicate with the lk console. The other is a pair of bulk endpoints which speak the protocol documented here. This interface is specified as:
Class: 0xff Subclass: 0xff Protocol: 0x00
Future versions may use other protocol numbers.
Zedmon packets are encapsulated in USB packets. The only common header is a 1 byte packet type field. Packet length and error detection is handled by USB. Some packets only contain the 1 byte packet type header and no payload. If a single report does not fit in a USB packet, the behavior is undefined.
The valid packet types are:
| ID | Dir | Description |
|---|---|---|
| 0x00 | H->T | Query Report Format |
| 0x01 | H->T | Query Time |
| 0x10 | H->T | Enable Reporting |
| 0x11 | H->T | Disable Reporting |
| 0x20 | H->T | Set Output |
| 0x80 | T->H | Report Format |
| 0x81 | T->H | Report |
| 0x82 | H->T | Timestamp |
The following data types are using in packets. Types with n/a IDs are not valid types for report data.
| ID | Type | Description |
|---|---|---|
| 0x00 | uint8 | Unsigned 8 Bit Integer |
| 0x01 | uint16 | Unsigned 16 Bit Little-Endian Integer |
| 0x03 | uint32 | Unsigned 32 Bit Little-Endian Integer |
| 0x04 | uint64 | Unsigned 64 Bit Little-Endian Integer |
| 0x10 | int8 | Signed 8 Bit Integer |
| 0x11 | int16 | Signed 16 Bit Little-Endian Integer |
| 0x13 | int32 | Signed 32 Bit Little-Endian Integer |
| 0x14 | int64 | Signed 64 Bit Little-Endian Integer |
| 0x20 | bool | Boolean Represented as a uint8 (non-zero == true). |
| 0x40 | float32 | 32 Bit Little-Endian IEEE-745 Floating Point |
| n/a | string | Null-Terminated ASCII Encoded String. |
The following units are used in report format packets:
| ID | Description |
|---|---|
| 0x00 | Amperes |
| 0x01 | Volts |
Requests the target send a Report Format packet. If the target responds with a Report Format packet with the Value Index of 0xff, this indicates that there is no value at that index. To enumerate the values, the host should start by requesting Value Index 0 and continue to request the next Value Index until receiving a packet with the index of 0xff.
Payload:
| Byte(s) | Format | Description |
|---|---|---|
| 0 | uint8 | Packet Type |
| 1 | uint8 | Value Index |
Requests the target send the current time in the local clock domain. The target responds with a Timestamp packet.
Payload: None
Requests the target start sending Report packets.
Payload: None
Requests the target stop sending Report packets.
Payload: None
Sets the indexed output to high/enabled (true) low/disabled (false). TODO(konkers): Add enumeration packets for outputs. Payload:
| Byte(s) | Format | Description |
|---|---|---|
| 0 | uint8 | Packet Type |
| 1 | uint8 | Output Index |
| 2 | bool | Output Value |
Payload:
| Byte(s) | Format | Description |
|---|---|---|
| 0 | uint8 | Packet Type |
| 1 | uint8 | Value Index |
| 2 | uint8 | Value Type |
| 3 | uint8 | Unit |
| 4..7 | float32 | Scale |
| 8..63 | string | Name |
Payload: One or more data reports of the following format. The length of each report is determined by the Report Format query responses. No partial reports will be included in a Report packet.
| Field | Format | Description |
|---|---|---|
| timestamp | uint64 | Timestamp, in microseconds, in the local clock domain. |
| value 0 | variable | Value of the 0th field described by the Report Format packets. |
| ... | ... | ... |
| value n | variable | Value of the nth field described by the Report Format packets. |
Payload:
| Field | Format | Description |
|---|---|---|
| timestamp | uint64 | Timestamp, in microseconds, in the local clock domain. |