python-cc1101/cc1101/__init__.py

import enum
import typing

import spidev


class CC1101:

    # > All transfers on the SPI interface are done
    # > most significant bit first.
    # > All transactions on the SPI interface start with
    # > a header byte containing a R/W bit, a access bit (B),
    # > and a 6-bit address (A5 - A0).
    # > [...]
    # > Table 45: SPI Address Space
    _WRITE_SINGLE_BYTE = 0x00
    # > Registers with consecutive addresses can be
    # > accessed in an efficient way by setting the
    # > burst bit (B) in the header byte. The address
    # > bits (A5 - A0) set the start address in an
    # > internal address counter. This counter is
    # > incremented by one each new byte [...]
    _WRITE_BURST = 0x40
    _READ_SINGLE_BYTE = 0x80
    _READ_BURST = 0xC0

    class _SPIAddress(enum.IntEnum):
        # see "Table 45: SPI Address Space"
        # > The configuration registers on the CC1101 are
        # > located on SPI addresses from 0x00 to 0x2E.
        FREQ2 = 0x0D
        FREQ1 = 0x0E
        FREQ0 = 0x0F
        # > For register addresses in the range 0x30-0x3D,
        # > the burst bit is used to select between
        # > status registers when burst bit is one, and
        # > between command strobes when burst bit is
        # > zero. [...]
        # > Because of this, burst access is not available
        # > for status registers and they must be accessed
        # > one at a time. The status registers can only be
        # > read.
        SRES = 0x30
        PARTNUM = 0x30
        VERSION = 0x31
        MARCSTATE = 0x35

    class MainRadioControlStateMachineState(enum.IntEnum):
        """
        MARCSTATE - Main Radio Control State Machine State
        """

        # > Figure 13: Simplified State Diagram
        IDLE = 0x01

    # 29.3 Status Register Details
    _SUPPORTED_PARTNUM = 0
    _SUPPORTED_VERSION = 0x14

    _CRYSTAL_OSCILLATOR_FREQUENCY_HERTZ = 26e6
    # see "21 Frequency Programming"
    # > f_carrier = f_XOSC / 2**16 * (FREQ + CHAN * ((256 + CHANSPC_M) * 2**CHANSPC_E-2))
    _FREQUENCY_CONTROL_WORD_HERTZ_FACTOR = _CRYSTAL_OSCILLATOR_FREQUENCY_HERTZ / 2 ** 16

    def __init__(self) -> None:
        self._spi = spidev.SpiDev()

    def _reset(self) -> None:
        # TODO check if 0 required
        assert self._spi.xfer([self._SPIAddress.SRES, 0]) == [0x0F, 0x0F]

    def _read_burst(self, start_register: _SPIAddress, length: int) -> typing.List[int]:
        response = self._spi.xfer([start_register | self._READ_BURST] + [0] * length)
        assert len(response) == length + 1, response
        assert response[0] == 0, response
        return response[1:]

    def _read_status_register(self, register: _SPIAddress) -> int:
        values = self._read_burst(start_register=register, length=1)
        assert len(values) == 1, values
        return values[0]

    def _write_burst(
        self, start_register: _SPIAddress, values: typing.List[int]
    ) -> None:
        response = self._spi.xfer([start_register | self._WRITE_BURST] + values)
        assert len(response) == len(values) + 1, response
        assert all(v == 0x0F for v in response), response  # TODO why?

    def __enter__(self) -> "CC1101":
        # https://docs.python.org/3/reference/datamodel.html#object.__enter__
        self._spi.open(0, 0)
        self._spi.max_speed_hz = 55700  # empirical
        self._reset()
        partnum = self._read_status_register(self._SPIAddress.PARTNUM)
        if partnum != self._SUPPORTED_PARTNUM:
            raise ValueError(
                "unexpected chip part number {} (expected: {})".format(
                    partnum, self._SUPPORTED_PARTNUM
                )
            )
        version = self._read_status_register(self._SPIAddress.VERSION)
        if version != self._SUPPORTED_VERSION:
            raise ValueError(
                "unexpected chip version number {} (expected: {})".format(
                    version, self._SUPPORTED_VERSION
                )
            )
        marcstate = self.get_main_radio_control_state_machine_state()
        if marcstate != self.MainRadioControlStateMachineState.IDLE:
            raise ValueError("expected marcstate idle (actual: {})".format(marcstate))
        return self

    def __exit__(self, exc_type, exc_value, traceback) -> bool:
        # https://docs.python.org/3/reference/datamodel.html#object.__exit__
        self._spi.close()
        return False

    def get_main_radio_control_state_machine_state(
        self
    ) -> MainRadioControlStateMachineState:
        return self.MainRadioControlStateMachineState(
            self._read_status_register(self._SPIAddress.MARCSTATE)
        )

    def get_marc_state(self) -> MainRadioControlStateMachineState:
        """
        alias for get_main_radio_control_state_machine_state()
        """
        return self.get_main_radio_control_state_machine_state()

    @classmethod
    def _frequency_control_word_to_hertz(cls, control_word: typing.List[int]) -> float:
        return (
            int.from_bytes(control_word, byteorder="big", signed=False)
            * cls._FREQUENCY_CONTROL_WORD_HERTZ_FACTOR
        )

    @classmethod
    def _hertz_to_frequency_control_word(cls, hertz: float) -> typing.List[int]:
        return list(
            round(hertz / cls._FREQUENCY_CONTROL_WORD_HERTZ_FACTOR).to_bytes(
                length=3, byteorder="big", signed=False
            )
        )

    def _get_base_frequency_control_word(self) -> typing.List[int]:
        # > The base or start frequency is set by the 24 bitfrequency
        # > word located in the FREQ2, FREQ1, FREQ0 registers.
        return self._read_burst(start_register=self._SPIAddress.FREQ2, length=3)

    def _set_base_frequency_control_word(self, control_word: typing.List[int]) -> None:
        self._write_burst(start_register=self._SPIAddress.FREQ2, values=control_word)

    def get_base_frequency_hertz(self) -> float:
        return self._frequency_control_word_to_hertz(
            self._get_base_frequency_control_word()
        )

    def set_base_frequency_hertz(self, freq: float) -> None:
        self._set_base_frequency_control_word(
            self._hertz_to_frequency_control_word(freq)
        )

    def __str__(self) -> str:
        return "CC1101(marcstate={}, base_frequency={:.2f}MHz)".format(
            self.get_main_radio_control_state_machine_state().name.lower(),
            self.get_base_frequency_hertz() / 10 ** 6,
        )