camrasdevices.py

"""HPIB wrappers for devices in the Dwingeloo telescope

This module contains some classes for conveniently working with the devices in the Dwingeloo
Telescope that communicate over GPIB (General Purpuse Interface Bus) or HPIB (presumably the
HP variant of GPIB). Currently, three of these devices exist, on different HPIB addresses:

- Receiver (address 1)
- Local Oscillator (address 28), used for mixing signals to downconvert them
- Clock Generator (address 14), used as the clock for the FPGA

For each of the three devices a class exists. Setting and getting the frequency of these
devices is done by using their `frequency` attribute.

Example:
    >>> import camrasdevices
    >>> lo = LocalOscillator()
    >>> lo.frequency
    <Quantity 1.0 GHz>
    >>> lo.frequency = 1.1e9
    >>> lo.frequency
    <Quantity 1.1 GHz>

By default, the setter method of `frequency` checks if setting the device succeeded. This is a
blocking operation, but the HPIB bus is quite fast.

    >>> lo.frequency = 1.e18
    Traceback (most recent call last):
    RuntimeError: Setting frequency failed: tried to set to 1e+18 Hz, it is now 1100000000.0 Hz

This checking can be disabled:

    >>> non_checking_lo = camrasdevices.LocalOscillator(check_frequency = False)
    >>> non_checking_lo.frequency = 1.e18
    >>> non_checking_lo.frequency
    <Quantity 1.1 GHz>

Other HPIB commands can be sent using the `command` function:
    >>> lo.command("loc 28") # Set device to local mode

Also generic HPIB commands (without specific address) can be sent:
    >>> lo.command("++eoi 1", prepend_address=False)

The CamrasHpibDevice class spawns one thread (shared with all instances) to perform the HPIB
commands. This is to make sure that instances living in separate threads do not interfere with
each other. The thread is a daemon, so it will be killed on program exit.

On initialization of the first CamrasDevice (or subclass), the command thread is initialized, and
some initialization commands are sent to the HPIB bus to tell it to use the appropriate line
endings etc.
"""

import astropy.units as u
from astropy.units import Quantity

import hpib
import serial.threaded


class CamrasHpibDevice(object):
    """Wrapper around HPIB commands"""

    command_thread = None

    def __init__(self, address, check_frequency=True):
        self.hpib_address = address
        self._check_frequency = check_frequency

        if not CamrasHpibDevice.command_thread:
            serial_port = serial.Serial("/dev/ttyUSB0")
            CamrasHpibDevice.command_thread = serial.threaded.ReaderThread(serial_port,
                                                                           hpib.GPIBProtocol)
            CamrasHpibDevice.command_thread.start()
            CamrasHpibDevice.command_thread._connection_made.wait()
            CamrasHpibDevice.command_thread.protocol.init_hpib()

    def command(self, command_string, prepend_address=True):
        """Send a command to the HPIB command thread

        Args:
            command_string (str): HPIB command
            prepend_address (bool): first send the address of this device

        Returns:
            str: output of the command (in case it was a query)
        """
        if prepend_address:
            address = self.address
        else:
            address = None

        return CamrasHpibDevice.command_thread.protocol.command(command_string, address)

    @property
    def frequency(self):
        """Frequency of the device as an astropy Quantity.

        Returns:
            Quantity: frequency (in Hz) of the device

        Raises:
            RuntimeError: If the device does not respond
        """
        freq_str = self.command("freq?")

        if not freq_str or len(freq_str) == 0:
            raise RuntimeError("Camras device at address {} is not responding".format(
                self.hpib_address))
        return int(float(freq_str)) * u.Hz

    @frequency.setter
    def frequency(self, freq):
        """Set the device to the specified frequency. Throws a RuntimeError if failed

        Args:
            freq (Union[float, Quantity]): new frequency. If no unit present, assume Hz

        Raises:
            RuntimeError: If the device sticks to a different frequency (e.g. if the specified
                frequency is outside the accepted range for the device)
        """
        if isinstance(freq, Quantity):
            freq = freq.to(u.Hz).value
        self.command("freq {:d} Hz".format(int(freq)))

        new_freq = self.frequency
        if self._check_frequency and new_freq.to(u.Hz).value != int(freq):
            raise RuntimeError("Setting frequency failed: tried to set to {}, it is now {}".format(
                freq, new_freq))


class Receiver(CamrasHpibDevice):
    """Wrapper around HPIB commands for the Rohde & Schwartz receiver"""

    def __init__(self, **kwargs):
        super(Receiver, self).__init__(1)


class LocalOscillator(CamrasHpibDevice):
    """Wrapper around HPIB commands for the local oscillator"""

    def __init__(self, **kwargs):
        super(LocalOscillator, self).__init__(28)


class ClockGenerator(CamrasHpibDevice):
    """Wrapper around HPIB commands for the clock generator (should be at 140MHz)"""

    def __init__(self, **kwargs):
        super(ClockGenerator, self).__init__(14)