Source code for baseband.mark5b.frame

# Licensed under the GPLv3 - see LICENSE
Definitions for VLBI Mark 5B frames.

Implements a Mark5BFrame class that can be used to hold a header and a
payload, providing access to the values encoded in both.

For the specification, see
import numpy as np

from ..base.frame import FrameBase
from .header import Mark5BHeader
from .payload import Mark5BPayload

__all__ = ['Mark5BFrame']

[docs]class Mark5BFrame(FrameBase): """Representation of a Mark 5B frame, consisting of a header and payload. Parameters ---------- header : `~baseband.mark5b.Mark5BHeader` Wrapper around the encoded header words, providing access to the header information. payload : `~baseband.mark5b.Mark5BPayload` Wrapper around the payload, provding mechanisms to decode it. valid : bool or None Whether the data are valid. If `None` (default), the validity will be determined by checking whether the payload consists of the fill pattern 0x11223344. verify : bool Whether to do basic verification of integrity (default: `True`) Notes ----- The Frame can also be read instantiated using class methods: fromfile : read header and payload from a filehandle fromdata : encode data as payload Of course, one can also do the opposite: tofile : method to write header and payload to filehandle data : property that yields full decoded payload A number of properties are defined: `shape`, `dtype` and `size` are the shape, type and number of complete samples of the data array, and `nbytes` the frame size in bytes. Furthermore, the frame acts as a dictionary, with keys those of the header. Any attribute that is not defined on the frame itself, such as ``.time`` will be looked up on the header as well. """ _header_class = Mark5BHeader _payload_class = Mark5BPayload _fill_pattern = 0x11223344 def __init__(self, header, payload, valid=None, verify=True): if valid is None: # Is this payload OK? Usually yes, so short-circuit on first few. valid = (payload.words[0] != self._fill_pattern or payload.words[1] != self._fill_pattern or payload.words[2] != self._fill_pattern or (payload.words[3:] != self._fill_pattern).any()) super().__init__(header, payload, valid, verify)
[docs] @classmethod def fromfile(cls, fh, *, kday=None, ref_time=None, sample_shape=(1,), bps=2, valid=None, verify=True): """Read a frame from a filehandle. Parameters ---------- fh : filehandle To read the header and payload from. kday : int or None Explicit thousands of MJD of the observation time. Can instead pass an approximate ``ref_time``. ref_time : `~astropy.time.Time` or None Reference time within 500 days of the observation time, used to infer the full MJD. Used only if ``kday`` is not given. sample_shape : tuple of int, optional Can have only one entry, the number of channels. Default: (1,). bps : int, optional Bits per elementary sample. Default: 2. verify : bool Whether to do basic checks of frame integrity (default: `True`). """ header = cls._header_class.fromfile(fh, kday=kday, ref_time=ref_time, verify=verify) payload = cls._payload_class.fromfile(fh, sample_shape=sample_shape, bps=bps) return cls(header, payload, valid, verify)
[docs] @classmethod def fromdata(cls, data, header=None, bps=2, valid=True, verify=True, **kwargs): """Construct frame from data and header. Parameters ---------- data : `~numpy.ndarray` Array holding data to be encoded. header : `~baseband.mark5b.Mark5BHeader` or None If not given, will attempt to generate one using the keywords. bps : int Bits per elementary sample. Default: 2. valid : bool Whether the data are valid (default: `True`). If not, the payload will be set to a fill pattern. verify : bool Whether to do basic checks of frame integrity (default: `True`). """ if header is None: header = Mark5BHeader.fromvalues(verify=verify, **kwargs) payload = cls._payload_class.fromdata(data, bps=bps) return cls(header, payload, valid=valid, verify=verify)
[docs] def tofile(self, fh): """Write encoded frame to filehandle.""" self.header.tofile(fh) if self.valid: self.payload.tofile(fh) else: fh.write(np.full_like(self.payload.words, self._fill_pattern).tobytes())