bambuddy/spoolbuddy/daemon/nau7802.py

"""NAU7802 24-bit ADC driver for load cell / scale applications.

I2C address: 0x2A
Bus: /dev/i2c-1 (GPIO2/GPIO3 on RPi)
"""

import logging
import os
import struct
import time

import smbus2

logger = logging.getLogger(__name__)


def _env_int(name: str, default: int) -> int:
    value = os.environ.get(name)
    if value is None or value == "":
        return default
    try:
        return int(value)
    except ValueError:
        return default


I2C_BUS = _env_int("SPOOLBUDDY_I2C_BUS", 1)
NAU7802_ADDR = 0x2A

# Register addresses
REG_PU_CTRL = 0x00
REG_CTRL1 = 0x01
REG_CTRL2 = 0x02
REG_ADCO_B2 = 0x12  # ADC output MSB
REG_ADCO_B1 = 0x13
REG_ADCO_B0 = 0x14  # ADC output LSB
REG_ADC = 0x15
REG_PGA = 0x1B
REG_PWR_CTRL = 0x1C
REG_REVISION = 0x1F

# PU_CTRL bits
PU_RR = 0x01  # Register reset
PU_PUD = 0x02  # Power up digital
PU_PUA = 0x04  # Power up analog
PU_PUR = 0x08  # Power up ready (read-only)
PU_CS = 0x10  # Cycle start
PU_CR = 0x20  # Cycle ready (read-only)
PU_OSCS = 0x40  # Oscillator select
PU_AVDDS = 0x80  # AVDD source select


class NAU7802:
    def __init__(self, bus: int = I2C_BUS, addr: int = NAU7802_ADDR):
        self._bus_num = bus
        self._bus = smbus2.SMBus(bus)
        self._addr = addr

    # CTRL2 bits for AFE calibration
    _CTRL2_CALS = 1 << 2
    _CTRL2_CAL_ERROR = 1 << 3

    def close(self):
        self._bus.close()

    def read_reg(self, reg: int) -> int:
        return self._bus.read_byte_data(self._addr, reg)

    def write_reg(self, reg: int, val: int):
        self._bus.write_byte_data(self._addr, reg, val & 0xFF)

    def _update_bits(self, reg: int, mask: int, value: int):
        cur = self.read_reg(reg)
        self.write_reg(reg, (cur & ~mask) | (value & mask))

    def _set_bit(self, reg: int, bit: int, enabled: bool):
        mask = 1 << bit
        self._update_bits(reg, mask, mask if enabled else 0)

    def _set_field(self, reg: int, shift: int, width: int, value: int):
        mask = ((1 << width) - 1) << shift
        self._update_bits(reg, mask, value << shift)

    def init(self):
        """Initialize NAU7802 per datasheet power-on sequencing (Section 8.1).

        Datasheet steps:
          1. RR=1 (reset all registers)
          2. RR=0, PUD=1 (enter normal operation; PUD auto-starts AD conversion)
          3. Wait ~200µs for PUR=1
          4. Configure (LDO, gain, rate, etc.)
          5. Tuning (ADC chopper, PGA caps)
          6. (Optional) calibration and flush transients
        """

        # Step 1: Reset (set RR=1, then RR=0)
        self._set_bit(REG_PU_CTRL, 0, True)  # RR=1
        time.sleep(0.010)
        self._set_bit(REG_PU_CTRL, 0, False)  # RR=0 exits reset
        # Datasheet says "about 200 microseconds" before PUR is set
        time.sleep(0.001)

        # Step 2: Power up digital (PUD=1 auto-starts AD conversion)
        self._set_bit(REG_PU_CTRL, 1, True)  # PUD=1
        # Step 2b: Power up analog (PUA=1)
        self._set_bit(REG_PU_CTRL, 2, True)  # PUA=1
        time.sleep(0.600)  # Wait for LDO and analog section to stabilize

        # Step 3: Wait for power-up ready (PUR bit 3)

        for _ in range(100):
            status = self.read_reg(REG_PU_CTRL)
            if status & PU_PUR:
                logger.debug("  Power-up ready")
                break
            time.sleep(0.001)
        else:
            raise TimeoutError("NAU7802 power-up timeout (PUR bit not set)")

        # Check revision register low nibble (datasheet expects 0xF).

        revision = self.read_reg(REG_REVISION)
        logger.debug(f"  Revision: 0x{revision:02X}")
        if (revision & 0x0F) != 0x0F:
            raise RuntimeError(f"Unexpected NAU7802 revision: 0x{revision:02X} (expected 0x_F)")

        # Step 4: Configure device
        # Internal LDO enable (AVDDS=1, bit 7) and set voltage to 3.0V

        self._set_bit(REG_PU_CTRL, 7, True)  # AVDDS=1
        self._set_field(REG_CTRL1, shift=3, width=3, value=0b101)  # VLDO=3.0V
        logger.debug("  LDO: 3.0V (internal)")

        # Set gain to 128x (CTRL1 bits 2:0 = 0b111)

        self._set_field(REG_CTRL1, shift=0, width=3, value=0b111)
        logger.debug("  Gain: 128x")

        # Set sample rate to 10 SPS (CTRL2 bits 6:4 = 0b000)
        # Note: At 10 SPS, each sample takes ~100ms; first 4 samples = ~400ms to settle

        self._set_field(REG_CTRL2, shift=4, width=3, value=0b000)
        logger.debug("  Sample rate: 10 SPS")

        # Step 5: Tuning per application notes
        # Disable ADC chopper clock (ADC bits 5:4 = 0b11)
        self._set_field(REG_ADC, shift=4, width=2, value=0b11)
        # Enable low-ESR caps on PGA (PGA bit 6 = 0 for improved accuracy)
        self._set_bit(REG_PGA, 6, False)

        # Step 6: Trigger fresh AD conversion and wait for first result
        # CS bit transition 0→1 starts fresh conversion; takes ~4-sample time for result

        self._set_bit(REG_PU_CTRL, 4, True)  # CS=1
        logger.debug("  Conversion started")

        # Flush startup transients before calibration
        # At 10 SPS, initial 4 samples may contain settling artifacts

        self.flush_readings(count=4, timeout_s=1.5)

        # Run AFE calibration (internal mode), then flush result
        self.calibrate_afe(timeout_ms=1000, mode=0)
        self.flush_readings(count=2, timeout_s=1.0)
        logger.debug("  Initialization complete")

    def begin_calibrate_afe(self, mode: int = 0) -> None:
        """Start asynchronous AFE calibration.

        mode values match NAU7802 CALMOD: 0=internal, 1=offset, 2=gain.
        """
        ctrl2 = self.read_reg(REG_CTRL2)
        ctrl2 &= 0xFC  # clear CALMOD bits[1:0]
        ctrl2 |= mode & 0x03
        self.write_reg(REG_CTRL2, ctrl2)

        # Set CALS (bit 2) to start calibration.
        self.write_reg(REG_CTRL2, self.read_reg(REG_CTRL2) | self._CTRL2_CALS)

    def wait_for_calibrate_afe(self, timeout_ms: int = 1000) -> bool:
        deadline = time.monotonic() + (timeout_ms / 1000.0) if timeout_ms > 0 else None

        while True:
            ctrl2 = self.read_reg(REG_CTRL2)
            if (ctrl2 & self._CTRL2_CALS) == 0:
                return (ctrl2 & self._CTRL2_CAL_ERROR) == 0

            if deadline is not None and time.monotonic() >= deadline:
                return False
            time.sleep(0.001)

    def calibrate_afe(self, timeout_ms: int = 1000, mode: int = 0) -> None:
        """Run AFE calibration per datasheet CTRL2[2] CALS bit sequence.

        Datasheet says:
          - Write 1 to CALS to start (mode in CALMOD bits [1:0])
          - CALS=1 during calibration, 0 when complete
          - Check CAL_ERR bit after completion
        """
        self.begin_calibrate_afe(mode=mode)
        if not self.wait_for_calibrate_afe(timeout_ms=timeout_ms):
            raise RuntimeError(f"NAU7802 AFE calibration timed out after {timeout_ms}ms")
        # Check CAL_ERR bit to ensure no error during calibration
        ctrl2 = self.read_reg(REG_CTRL2)
        if ctrl2 & self._CTRL2_CAL_ERROR:
            raise RuntimeError("NAU7802 AFE calibration completed with CAL_ERR set")
        logger.debug("  AFE calibration: OK")

    def wait_data_ready(self, timeout_s: float = 1.0) -> bool:
        deadline = time.monotonic() + timeout_s
        while time.monotonic() < deadline:
            if self.data_ready():
                return True
            time.sleep(0.001)
        return False

    def flush_readings(self, count: int = 4, timeout_s: float = 1.0) -> None:
        flushed = 0
        while flushed < count:
            if not self.wait_data_ready(timeout_s=timeout_s):
                raise TimeoutError("Timeout while flushing startup scale readings")
            _ = self.read_raw()
            flushed += 1

    def data_ready(self) -> bool:
        return bool(self.read_reg(REG_PU_CTRL) & PU_CR)

    def read_raw(self) -> int:
        """Read 24-bit signed ADC value."""
        b2 = self.read_reg(REG_ADCO_B2)
        b1 = self.read_reg(REG_ADCO_B1)
        b0 = self.read_reg(REG_ADCO_B0)
        raw = (b2 << 16) | (b1 << 8) | b0
        # Sign extend 24-bit to 32-bit
        if raw & 0x800000:
            raw |= 0xFF000000
            raw = struct.unpack("i", struct.pack("I", raw))[0]
        return raw