Frames format - PW-Sat2/PWSat2OBC GitHub Wiki
PW-Sat2 frame was derived from CCSDS space packet protocol: Link.
Each file inside memory will be assigned unique APID (application ID), and within the file each 235-byte block will be assigned unique SEQ (Sequence counter). This leads to assumption that each 235-byte block in memory will be addressable and accessible from GS.
APID and SEQ will be added to each frame transmitted via radiolink to make identification and merging possible on ground:
| header | data | |
| APID | SEQ | |
| 6 bits | 18 bits | 1856 bits |
| Security code | APID | Payload |
|---|---|---|
| 32 bits | 8 bits (TBC) | 1560 bits |
- Security code acts as authentication token that allows OBC to discard frames unauthorized ground station. That will be embedded into code and kept in secret.
- APID identifies type of telecommand being sent.
- Telecommands which carries more data that can fit in payload of single frame will contain sequence number inside payload field. As that type of telecommands are rare it is not necessary to handle that situation on low level as it can be solved on per telecommand basis