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CDNET is a high layer protocol for CDBUS

  1. CDNET Levels
  2. Level 0 Format
  3. Level 1 Format
  4. Level 2 Format
  5. Port Allocation Recommendation
  6. Examples
  7. More Resources

CDBUS frame:
[src, dst, len] + [CDNET payload] + [crc_l, crc_h]

CDNET Levels

CDNET protocol has three different levels, select by bit7 and bit6 of first byte:

Bit7 Bit6 DESCRIPTION
0 x Level 0: The simplest one, for single network communication
1 0 Level 1: Support cross network and multi-cast communication
1 1 Level 2: Raw, e.g. TCP/IP communication between PCs

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

The CDNET is little endian.

Level 0 Format

Request

First byte:

FIELD DESCRIPTION
[7] Always 0: Level 0
[6] Always 0: request
[5:0] dst_port, range 0 ~ 0x3f

The second byte and after: command parameters.

Note: The port is equivalent to UDP port, but can be simply understood as commands.

Reply

First byte:

FIELD DESCRIPTION
[7] Always 0: Level 0
[6] Always 1: reply
[5] 0: not share; 1: [4:0] shared for first data byte
[4:0] Not care, or part of first data byte

Default: SHARE_MASK is 0xe0, SHARE_LEFT is 0x80, only allow share if (first data byte & SHARE_MASK) == SHARE_LEFT.

E.g.: reply [0x40, 0x8c] is the same as [0x6c].

0x40: 'b0100_0000
0x8c: 'b1000_1100
----
0x6c: 'b0110_1100

The first byte shared part, and the second byte and after: reply status and/or datas.

Recommendation for level 0 and 1:

For request and report, the first parameter byte is sub command with two flags:

FIELD DESCRIPTION
[7] is_reply, always 0
[6] not_reply, e.g. 1 for report packet
[5:0] sub command

For reply, the first data byte is status with one flag:

FIELD DESCRIPTION
[7] is_reply, always 1
[6:0] status, 0 means no error

Level 1 Format

First byte:

FIELD DESCRIPTION
[7] Always 1
[6] Always 0
[5] MULTI_NET
[4] MULTICAST
[3] SEQUENCE
[2:0] PORT_SIZE

MULTI_NET & MULTICAST

MULTI_NET MULTICAST DESCRIPTION
0 0 Local net: append 0 byte
0 1 Local net multicast: append 2 bytes [mh, ml]
1 0 Cross net: append 4 bytes: [src_net, src_mac, dst_net, dst_mac]
1 1 Cross net multicast: append 4 bytes: [src_net, src_mac, mh, ml]

Notes:

  • mh + ml: multicast_id, ml is mapped to mac layer multicast address;
  • Could simply use MULTI_NET = 0 and MULTICAST = 0 for local net multicast and broadcast.

SEQUENCE

0: No sequence number;
1: Append 1 byte SEQ_NUM, see Port 0.

PORT_SIZE:

Bit2 Bit1 Bit0 SRC_PORT DST_PORT
0 0 0 Default port 1 byte
0 0 1 Default port 2 bytes
0 1 0 1 byte Default port
0 1 1 2 bytes Default port
1 0 0 1 byte 1 byte
1 0 1 1 byte 2 bytes
1 1 0 2 bytes 1 byte
1 1 1 2 bytes 2 bytes

Notes:

  • Default port is 0xcdcd for convention, it does not take up space.
  • Append bytes for src_port first then dst_port.

Level 2 Format

First byte:

FIELD DESCRIPTION
[7] Always 1
[6] Always 1
[5:4] FRAGMENT
[3] SEQUENCE
[2:0] User-defined flag

FRAGMENT:

Bit5 Bit4 DST_PORT
0 0 Not fragment
0 1 First fragment
1 0 More fragment
1 1 Last fragment

Note:

  • SEQUENCE must be selected when using fragments.
  • There is no need to reset the SEQ_NUM when starting the fragmentation.

SEQUENCE

0: No sequence number;
1: Append 1 byte SEQ_NUM, see Port 0.

Port Allocation Recommendation

It is recommended that ports 0 to 0xf be used for general purpose. Among them, port 0 is used for sequence control of cdnet, and port 1 is used for device information query.

All ports in this section are optional, but it is recommended to implement the first function of port 1 (read device_info).

Port 0

Used together with header's SEQUENCE for flow control and ensure data integrity.
The SEQ_NUM[6:0] auto increase when SEQUENCE is selected in the header.
Bit 7 of SEQ_NUM is set indicating that a report is required.
Do not select SEQUENCE for port 0 communication.

Port 0 communications:

Check the SEQ_NUM:
  Write [0x00]
  Return: [0x80, SEQ_NUM] (no record found if bit 7 set)

Set the SEQ_NUM:
  Write [0x20, SEQ_NUM]
  Return: [0x80]

Report SEQ_NUM:
  Report [0x40, SEQ_NUM] (report to the src port of the relevant packet)

Example:
(The data format is cdnet payload. dft is short for default (0xcdcd). (p) marks the location of the port.)

Device A                    Device B                 Description                    Port flow
        (p)
[0x80, 0x00, 0x20, 0x00] >>         (p)              Set SEQ_NUM at first time      (dft -> 0x0)
                         << [0x82, 0x00, 0x80]       Port 0 reply                   (dft <- 0x0)
              (p)
[0x88, 0x00, 0x10, ...]  >>                          Start send data                (dft -> 0x10)
[0x88, 0x01, 0x10, ...]  >>                                                         (dft -> 0x10)
[0x88, 0x82, 0x10, ...]  >>                          Require report at SEQ_NUM 2    (dft -> 0x10)
[0x88, 0x03, 0x10, ...]  >>                                                         (dft -> 0x10)
[0x88, 0x04, 0x10, ...]  >>         (p)                                             (dft -> 0x10)
              (p)        << [0x82, 0x00, 0x40, 0x03] Report after receive SEQ_NUM 2 (dft <- 0x0)
[0x88, 0x85, 0x10, ...]  >>         (p)              Require report at SEQ_NUM 5    (dft -> 0x10)
                         << [0x82, 0x00, 0x40, 0x06] Report after receive SEQ_NUM 5 (dft <- 0x0)
              (p)
[0x88, 0x86, 0x11, ...]  >>         (p)              Require report at SEQ_NUM 6    (dft -> 0x11)
                         << [0x82, 0x00, 0x40, 0x07] Report after receive SEQ_NUM 6 (dft <- 0x0)
                         << [0x82, 0x11, ...]        Reply without SEQ by default   (dft <- 0x11)

Port 1

Provide device info.

Type of mac_start and mac_end is uint8_t;
Type of max_time is uint16_t, unit: ms;
Type of "string" is any length of string, include empty;
All strings excluding the terminating null byte ('\0').

Read device_info string:
  Write [0x00]
  Return [0x80, "device_info"]

Search device by filters (used to resolve mac conflicts):
  Write [0x10, max_time, mac_start, mac_end, "string"]
  Return [0x80, "device_info"] after a random time in range [0, max_time]
    only if "device_info" contain "string" (always true for empty string) and
    current mac address is in the range [mac_start, mac_end], mac_end included
  Not return otherwise
    and reject any subsequent modify mac (or save config) commands

Example of device_info:
M: model; S: serial string; HW: hardware version; SW: software version ...
Do not care about the field order, and should at least include the model field.

Examples

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: [0x60, 0x4d, 0x3a, 0x20 ... 0x34] (first 0x60 is 0x40 + 0x80)
    • CDBUS frame: [0x0d, 0x0c, 0x0f, 0x60, 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]

Code Examples

How to use this library refer to cd_mdrv_step (stepper motor controller), cdbus_bridge or cdnet_tun projects;
How to control CDCTL-Bx/Hx refer to dev/cdctl_xxx.

More Resources

Python library for CDNET: ../pycdnet

CDNET address string format: parser/cdnet.h

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CDNET Protocol and CDBUS / CDNET C Library (The library is MCU-oriented.)

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