0 Fork 0

Files

T

Add comprehensive spec audit results and pyMC_core issue reports

- CHANGELOG.md: Full audit findings organized by severity
- PYMC_CORE_ISSUES.md: 7 evidence-based bug reports for pyMC_core
  (wrong constants, broken path_len decoding, wrong TRACE hash,
  wrong SNR calculation)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add comprehensive spec audit results and pyMC_core issue reports

- CHANGELOG.md: Full audit findings organized by severity
- PYMC_CORE_ISSUES.md: 7 evidence-based bug reports for pyMC_core
  (wrong constants, broken path_len decoding, wrong TRACE hash,
  wrong SNR calculation)
- Remove ERRATA.md: contents already covered by audit findings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

2026-04-01 21:37:57 -06:00

2.5 KiB

Raw Blame History

MeshCore Protocol Specification

Section 11: Payload — Multipart

Overview

The MULTIPART payload wraps another payload type to indicate it is part of a multi-packet sequence. The first byte encodes the number of remaining packets in the sequence and the sub-payload type. Currently, only multipart ACK is defined in the reference implementation.

Payload Type

Header payload type field: 0x0A (MULTIPART)

Wire Format

 0                   1
 0 1 2 3 4 5 6 7 8 9 0 ...
+-+-+-+-+-+-+-+-+-+-+-+-+
|Rem|  SubType  | Sub-payload  |
+-+-+-+-+-+-+-+-+-+-+-+-+

First byte encoding:

  Bit:  7   6   5   4   3   2   1   0
      +---+---+---+---+---+---+---+---+
      | Remaining (4) |  Sub-Type (4) |
      +---+---+---+---+---+---+---+---+

Fields

Field	Offset	Size	Type	Description
remaining	0 (bits 4-7)	4 bits	uint	Number of remaining packets in sequence (0-15)
sub_type	0 (bits 0-3)	4 bits	uint	Payload type of the wrapped content
sub_payload	1	variable	raw	The wrapped payload data

first_byte = (remaining << 4) | (sub_type & 0x0F)

Multipart ACK

The only currently defined multipart sub-type is ACK (sub_type = 0x03):

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  (rem<<4)|0x03|                ACK CRC (uint32_le)            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Total payload: 5 bytes (1 byte header + 4 byte CRC).

Multipart ACKs are used to send additional ACK retransmissions for reliability. The remaining field indicates how many more ACK packets follow this one.

Encoding (Multipart ACK)

Set first byte to (remaining << 4) | PAYLOAD_TYPE_ACK.
Copy the 4-byte ACK CRC starting at offset 1.
Set payload_len to 5.

Decoding (Multipart ACK)

Read first byte. Extract remaining = byte >> 4, sub_type = byte & 0x0F.
If sub_type == 0x03 (ACK) and payload_len >= 5: a. Read 4 bytes at offset 1 as ACK CRC (uint32_le).
For other sub_types: reserved for future use.

Constraints

Payload MUST be at least 2 bytes (1 header + 1 sub-payload minimum).
For multipart ACK, payload MUST be at least 5 bytes.

Cross-References

Section 4: ACK — ACK CRC format
Test vectors: corpus/payloads/multipart/

Reference Implementation

Mesh::createMultiAck() in src/Mesh.cpp — Encoding
Mesh::onRecvPacket(), case PAYLOAD_TYPE_MULTIPART — Decoding

2.5 KiB Raw Blame History