Generating XTCE¶

Once the tree is built, each top-level system exports itself with dump() (to a file-like object) or dumps() (to a string):

with open("mysat.xml", "wt") as f:
    satellite.dump(f)

xml = satellite.dumps()

Every top-level system produces one XTCE file; a model with a spacecraft system and a GSE system is exported as two files.

Export options¶

Both methods accept the same keyword-only options:

format: "xtce-1.2" (the default, natively supported by Yamcs) or "xtce-1.3".
indent: Indentation string per level, default two spaces. Use "" for the most compact output.
top_comment: The XML comment inserted at the top of the file. By default this is a notice that the file is generated; pass a string to customize it, or False to omit it.
skip_parameters, skip_containers, skip_commands, skip_algorithms, skip_subsystems: Leave the corresponding sections out of the export. Useful for partial exports, e.g. producing a telemetry-only file.

If the model contains something that cannot be represented in the chosen format, the export raises ExportError with a message naming the offending item. Since generation walks the entire tree, running the export is also the quickest overall sanity check of a model.

Loading into Yamcs¶

Reference the generated file(s) from the mdb section of the Yamcs instance configuration:

etc/yamcs.myinstance.yaml¶

mdb:
  - type: xtce
    args:
      file: mdb/mysat.xml
  - type: xtce
    args:
      file: mdb/gse.xml

Yamcs reads the file at startup: after regenerating, restart Yamcs (or the instance) to pick up the changes.

Validation checks¶

The yamcs.pymdb.checks module offers read-only sanity checks to run over a finished model, before or alongside the export. Each function walks the full tree, prints a line per finding, and returns True when all is well — convenient for turning into a build failure:

from yamcs.pymdb import checks

ok = checks.check_complete_verifiers(satellite)
ok &= checks.check_float_encoding(satellite)
assert ok, "MDB validation failed"

Function	Verifies that…
`check_complete_verifiers`	every non-abstract command has a verifier able to complete it successfully (see Command Verification)
`check_float_encoding`	no 32-bit float parameter/argument uses a 64-bit encoding (a common precision bug)
`check_little_endian_only`	all multi-byte integer encodings are little endian — for projects whose hardware is uniformly little endian, this catches a forgotten `le` variant

These checks are optional helpers, not part of the export; a model that fails them still exports fine.

Errors¶

The library raises three exception types of its own:

`ExportError`	The model cannot be represented in the requested XTCE format.
`DuplicateNameError`	An object was created with a name already used by a sibling of the same kind (see Systems and Subsystems).
`SizeCalculationError`	A fixed bit size could not be determined, e.g. `Container.fit_entries()` over a dynamically sized entry.