pynq.iop.pmod_tmp2 — Python productivity for Zynq (Pynq) v1.0

# Source code for pynq.iop.pmod_tmp2

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    __author__      = "Cathal McCabe, Yun Rock Qu"
    __copyright__   = "Copyright 2016, Xilinx"
    __email__       = "pynq_support@xilinx.com"

    import time
    from pynq import MMIO
    from pynq.iop import request_iop
    from pynq.iop import iop_const
    from pynq.iop import PMODA
    from pynq.iop import PMODB

    PMOD_TMP2_PROGRAM = "pmod_tmp2.bin"
    PMOD_TMP2_LOG_START = iop_const.MAILBOX_OFFSET+16
    PMOD_TMP2_LOG_END = PMOD_TMP2_LOG_START+(1000*4)

    class Pmod_TMP2(object):
        """This class controls a temperature sensor Pmod.

        The Pmod TMP2 (PB 200-221) is an ambient temperature sensor powered by
        ADT7420.

        Attributes
        ----------
        iop : _IOP
            I/O processor instance used by TMP2.
        mmio : MMIO
            Memory-mapped I/O instance to read and write instructions and data.
        log_interval_ms : int
            Time in milliseconds between sampled reads of the TMP2 sensor.

        """
        def __init__(self, if_id):
            """Return a new instance of a TMP2 object.

            Parameters
            ----------
            if_id : int
                The interface ID (1, 2) corresponding to (PMODA, PMODB).

            """
            if not if_id in [PMODA, PMODB]:
                raise ValueError("No such IOP for Pmod device.")

            self.iop = request_iop(if_id, PMOD_TMP2_PROGRAM)
            self.mmio = self.iop.mmio
            self.log_interval_ms = 1000

            self.iop.start()

        def read(self):
            """Read current temperature value measured by the Pmod TMP2.

            Parameters
            ----------
            None

            Returns
            -------
            float
                The current sensor value.

            """
            self.mmio.write(iop_const.MAILBOX_OFFSET+\
                            iop_const.MAILBOX_PY2IOP_CMD_OFFSET, 3)

            while (self.mmio.read(iop_const.MAILBOX_OFFSET+\
                                    iop_const.MAILBOX_PY2IOP_CMD_OFFSET) == 3):
                pass

            value = self.mmio.read(iop_const.MAILBOX_OFFSET)
            return self._reg2float(value)

        def set_log_interval_ms(self,log_interval_ms):
            """Set the sampling interval for the Pmod TMP2.

            Parameters
            ----------
            log_interval_ms : int
                Time in milliseconds between sampled reads of the TMP2 sensor

            Returns
            -------
            None

            """
            if (log_interval_ms < 0):
                raise ValueError("Log length should not be less than 0.")

            self.log_interval_ms = log_interval_ms
            self.mmio.write(iop_const.MAILBOX_OFFSET+4, self.log_interval_ms)

        def start_log(self):
            """Start recording multiple values in a log.

            This method will first call set_log_interval_ms() before writting to
            the MMIO.

            Parameters
            ----------
            None

            Returns
            -------
            None

            """
            self.set_log_interval_ms(self.log_interval_ms)
            self.mmio.write(iop_const.MAILBOX_OFFSET+\
                            iop_const.MAILBOX_PY2IOP_CMD_OFFSET, 7)

        def stop_log(self):
            """Stop recording multiple values in a log.

            Simply write to the MMIO to stop the log.

            Parameters
            ----------
            None

            Returns
            -------
            None

            """
            self.mmio.write(iop_const.MAILBOX_OFFSET+\
                            iop_const.MAILBOX_PY2IOP_CMD_OFFSET, 1)

        def get_log(self):
            """Return list of logged samples.

            Parameters
            ----------
            None

            Returns
            -------
            List of valid samples from the temperature sensor in Celsius.

            """
            # First stop logging
            self.stop_log()

            # Prep iterators and results list
            head_ptr = self.mmio.read(iop_const.MAILBOX_OFFSET+0x8)
            tail_ptr = self.mmio.read(iop_const.MAILBOX_OFFSET+0xC)
            temps = list()

            # Sweep circular buffer for samples
            if head_ptr == tail_ptr:
                return None
            elif head_ptr < tail_ptr:
                for i in range(head_ptr,tail_ptr,4):
                    temps.append(self._reg2float(self.mmio.read(i)))
            else:
                for i in range(head_ptr,PMOD_TMP2_LOG_END,4):
                    temps.append(self._reg2float(self.mmio.read(i)))
                for i in range(PMOD_TMP2_LOG_START,tail_ptr,4):
                    temps.append(self._reg2float(self.mmio.read(i)))
            return temps

        def _reg2float(self, reg):
            """Translate the register value to a floating-point number.

            Note
            ----
            The float precision is specified to be 1 digit after the decimal
            point.

            Bit [31]    (1 bit)        ->    Sign (S)
            Bit [30:23] (8 bits)       ->    Exponent (E)
            Bit [22:0]  (23 bits)      ->    Mantissa (M)

            Parameters
            ----------
            reg : int
                A 4-byte integer.

            Returns
            -------
            float
                The floating-point number translated from the input.

            """
            if reg == 0:
                return 0.0
            sign = (reg & 0x80000000) >> 31 & 0x01
            exp = ((reg & 0x7f800000) >> 23)-127
            if (exp == 0):
                man = (reg & 0x007fffff)/pow(2,23)
            else:
                man = 1+(reg & 0x007fffff)/pow(2,23)
            result = pow(2,exp)*(man)*((sign*-2) +1)
            return float("{0:.1f}".format(result))