Trice message encoding

Trice Legacy Encoding. For TREX see 1.0 Spec

Trice Legacy Encoding. For TREX see 1.0 Spec

Trice Legacy Encoding. For TREX see 1.0 Spec

Trice Legacy Encoding. For TREX see 1.0 Spec

Trice Legacy Encoding. For TREX see 1.0 Spec

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• 1. COBS encoding and user protocols
• 1. [COBS](https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing) encoding for re-sync after data disruption
• 1. 32-bit transfer chunks
     • 3.1. Example: zero-delimited 7-bytes COBS package
     • 3.2. Example: zero-delimited 8-bytes COBS package:
• 1. Package mode prefix
     • 4.1. Example: 12 byte trice message buffer prefixed with mode 0 (no time stamps):
     • 4.2. Example: 16 byte trice message buffer prefixed with mode 1 (time stamps)
     • 4.3. Example: 12-bytes user packet - will be ignored by the trice tool:

1. COBS encoding and user protocols

• The Consistent Overhead Byte Stuffing technique is a very powerful and simple way for re-syncing.
• Just in case, wait for the next package delimiter.
• Several Trice message can occur within one single COBS package.
• Each COBS package starts with a 32-bit descriptor:

Descriptor	Meaning
0x00000000	Trice message(s) without prefix
0x00000001	Trice message(s) with 32-bit target timestamp
0x00000002	Trice message(s) with 32-bit target location
0x00000003	Trice message(s) with 64-bit target timestamp and location
0x00000004…0x000000FF	Reserved for Trice encodings
0x00000100…0xFFFFFFFF	User protocol data, the trice tool ignores them

• This allows intermixing of several data streams with Trice data.
• After the 4 COBS package descriptor bytes start several full Trice messages.
• In dependence of the COBS package descriptor each Trice message is prefixed with 0, 32 or 64 bit additional information: target code location and target timestamp.
• The detailed Trice encoding is derivable from trice.h and not repeated here to avoid unnecessary errors.

2. COBS encoding for re-sync after data disruption

• After a data transmission disruption, reliable re-sync should be possible.
• The COBS techique gives this possibility in an easy way: simply wait for the next packet delimiter byte (usually 0).
• Therefore all Trice transfers are COBS encoded.

3. 32-bit transfer chunks

• A Trice data stream comes always in a multiple-of-4 length for effective transfer.
  • After COBS encoding the length is the same or 1.04 times longer.
  • Therefore after COBS encoding the packages are delimited by 1 to 4 zeroes.
  • After the first zero delimiter, 0 to 3 padding zeroes are ignored as len-0 packages.

3.1. Example: zero-delimited 7-bytes COBS package

cobs	cobs	cobs	cobs	cobs	cobs	cobs	delimiter
x	x	x	x	x	x	x	0
0	1	2	3	4	5	6	7

3.2. Example: zero-delimited 8-bytes COBS package:

cobs	cobs	cobs	cobs	cobs	cobs	cobs	cobs	delimiter	padding	padding	padding
x	x	x	x	x	x	x	x	0	0	0	0
0	1	2	3	4	5	6	7	8	9	10	11

4. Package mode prefix

• Trice messages are always multiple-of-4-bytes messages.
• A Trice buffer can contain several trice messages.
  • Each single trice carries its own length information.
• Just before buffer encoding takes part, a 32-bit buffer mode value is prefixed:
  • buffer mode 0: Trice messages are without embedded device timestamps.
  • buffer mode 1: Trice messages are prefixed with 32-bit embedded device timestamps.
  • buffer mode 2: Trice messages are prefixed with 32-bit embedded device source location information.
  • buffer mode 3: Trice messages are prefixed with 64-bit embedded device source location information and timestamp.
  • buffer mode 4-15: Reserved. The trice tool ignores such package.
  • buffer mode 16-0xFFFFFFFF: user mode values. The trice tool ignores such package. This way any user protocols transferable over the same line.

4.1. Example: 12 byte trice message buffer prefixed with mode 0 (no time stamps):

• The 12 trice bytes could be 1, 2 or 3 trice messages consisting of 3, 2 or 1 32-Bit values.

mode	mode	mode	mode	data	data	data	data	data	data	data	data	data	data	data	data
0	0	0	0	x	x	x	x	x	x	x	x	x	x	x	x
0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15

4.2. Example: 16 byte trice message buffer prefixed with mode 1 (time stamps)

• The 16 trice bytes could be 1 or 2 trice messages consisting of 3 or 1 32-bit values, each prefixed by a target timestamp.

mode	mode	mode	mode	data	data	data	data	data	data	data	data	data	data	data	data	data	data	data	data
1	0	0	0	t	t	t	t	x	x	x	x	t|x	t|x	t|x	t|x	x	x	x	x
0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19

4.3. Example: 12-bytes user packet - will be ignored by the trice tool:

mode	mode	mode	mode	data	data	data	data	data	data	data	data	data	data	data	data
0	1	0	0	x	x	x	x	x	x	x	x	x	x	x	x
0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15