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Protocol status: Stable [Version 1.0]

The CDBUS frame containing a CDNET package is as follows:
[src, dst, len] + [CDNET package] + [crc_l, crc_h]
[src, dst, len] + [CDNET header, payload] + [crc_l, crc_h]

CDNET protocol offers two levels, determined by bit7 of the first header byte:

You can select one or more levels for your application as required.

The CDNET is little endian.

A single-byte header:

Note: The port is analogous to UDP port and can be thought of simply as command.

A single-byte header:

The first payload byte omits bits [7:6], which were intended to beb10.

E.g.: Header0x42 implies0x82 as the first byte of the payload.

The first byte of the header:

Notes:

• mh + ml: multicast_id, ml is mapped to mac layer multicast address (h: high byte, l: low byte);
• Could simply use MULTI_NET = 0 and MULTICAST = 0 for local net multicast and broadcast.
• Implementations of MULTI_NET and MULTICAST are optional.

Notes:

• The default port is0xcdcd for convention and doesn't consume space.
• Append bytes forsrc_port beforedst_port.
• Implementation of 2-byte port is optional.

For Request and Report, the first byte definition:

For Reply, the first byte definition:

Ports 0 to 0xf are recommended for general purposes.Specifically, port 1 is designated for device information queries.While all ports in this section are optional, it is advisable to implement the basic function of port 1 (read device_info).

Provide device info.

Types: - mac_start and mac_end: uint8_t - max_time: uint16_t (unit: ms) - "string": variable-length string, including empty string   (excluding the terminating null byte '\0')Read device_info string:  Write [0x00]  Return [0x80, "device_info"]Search devices by filters (for resolving mac conflicts):  Write [0x10, max_time, mac_start, mac_end, "string"]  Return [0x80, "device_info"] after a random time in the range [0, max_time]    only if "device_info" contains "string" (always true for an empty string)    and the current mac address is in the range [mac_start, mac_end] (inclusive)  Not return otherwise    and reject any subsequent modify mac (or save config) commands

Example ofdevice_info:
M: model; S: serial id; HW: hardware version; SW: software version ...
Field order is not important; it is recommended to include the model field at least.

           localhost      local link     unique local    multicast            10:00:00level0:                    00:NN:MMlevel1:                    80:NN:MM        a0:NN:MM       f0:MH:ML

Notes:

• NN: net_id, MM: mac_addr, MH+ML: multicast_id (H: high byte, L: low byte).
• The string address is analogous to IPv6 address.

Request device info:
(Local network, requester's mac address:0x0c, target's mac address:0x0d)

Reply the device info string:"M: c1; S: 1234",expressed in hexadecimal:[0x4d, 0x3a, 0x20, 0x63, 0x31, 0x3b, 0x20, 0x53, 0x3a, 0x20, 0x31, 0x32, 0x33, 0x34].

The Level 0 Format:

• Request:
  • CDNET socket:[00:00:0c]:0xcdcd ->[00:00:0d]:1:0x00 (net id:0)
  • CDNET packet:[0x01, 0x00] (dst_port:0x01)
  • CDBUS frame:[0x0c, 0x0d, 0x02, 0x01, 0x00, crc_l, crc_h]
• Reply:
  • CDNET socket:[00:00:0d]:1 ->[00:00:0c]:0xcdcd:0x80 +"M: c1; S: 1234"
  • CDNET packet:[0x40, 0x4d, 0x3a, 0x20 ... 0x34] (first0x40 implies payload byte0x80)
  • CDBUS frame:[0x0d, 0x0c, 0x0f, 0x40, 0x4d, 0x3a, 0x20 ... 0x34, crc_l, crc_h]

The Level 1 Format:

• Request:
  • CDNET socket:[80:00:0c]:0xcdcd ->[80:00:0d]:1:0x00
  • CDNET packet:[0x80, 0x01, 0x00] (src_port: default,dst_port:0x01)
  • CDBUS frame:[0x0c, 0x0d, 0x03, 0x80, 0x01, 0x00, crc_l, crc_h]
• Reply:
  • CDNET socket:[80:00:0d]:1 ->[80:00:0c]:0xcdcd:0x80 +"M: c1; S: 1234"
  • CDNET packet:[0x82, 0x01, 0x80, 0x4d, 0x3a, 0x20 ... 0x34] (src_port:0x01,dst_port: default)
  • CDBUS frame:[0x0d, 0x0c, 0x11, 0x82, 0x01, 0x80, 0x4d, 0x3a, 0x20 ... 0x34, crc_l, crc_h]

For transferring large data, such as transmitting a jpg image in thecdcam project, the sub command is defined as follows:

[5:4] FRAGMENT: 00: not fragment, 01: first, 10: more, 11: last, [3:0]: cnt

Here, thecnt value corresponds to 0 for the first packet, and increments by 1 for each subsequent packet.

If flow control is required, for example, we can group every 12 packets as a transmission set,where only the last packet in each set hasnot_reply set to 0. Start by transmitting 2 sets of packets,wait for a reply regarding the last packet in the first set, and then append another set of packets.

For sub commands that do not have acnt definition like the one mentioned above,if we want to ensure the uniqueness of a command, such as ensuring that a command can only be executed once,we can also achieve this by cyclically sending commands through multiple source port numbers.

This way, if a command does not receive a reply, resend the command.The receiving port checks whether the source port number of the received command matches that of the previous command;if they match, the command is not executed again.