feat: cleanup interface and leverage inheritance (#51)

The initial implementation tried to separate the low-level interface to
the EMC2101's functionality from the high-level interfaces (PWM & DAC).
This lead to significant code duplication between EMC2101_Core and
EMC2101_PWM. This duplication would only get worse once EMC2101_DAC is
added.

The redesigned interface scraps that distinction and instead leverages
inheritance to remove code duplication. This is expected to result in a
cleaner and easier to manage code base.

notable changes:
 - remove code duplication between EMC2101_Core and EMC2101_PWM
 - rework the initialization logic for the low-level implementation
 - rename 'chip' and 'external' sensore to 'its' and 'ets'
   (the external temperature sensor had many different names - these
   have been cleaned up)
 - redesign lookup table into a low-level and an extended implementation
   (The low-level implementation exclusively supports steps and has no
   concept of a percentage or RPM. PWM and DAC implementation need to
   provide the required logic to convert Percentage and RPM into steps.)
 - eliminate no longer required intermediate functionality

Author: feeph

feeph/emc2101/__init__.py

@@ -47,6 +47,8 @@
 # the following imports are provided for user convenience
 # flake8: noqa: F401
 from feeph.emc2101.calibration import calibrate_pwm_fan
+from feeph.emc2101.config_register import ConfigRegister
 from feeph.emc2101.core import CONVERSIONS_PER_SECOND, DEFAULTS, ExternalSensorStatus, SpinUpDuration, SpinUpStrength
+from feeph.emc2101.ets_config import ExternalTemperatureSensorConfig, ets_2n3904, ets_2n3906
 from feeph.emc2101.fan_configs import FanConfig, RpmControlMode, Steps, export_fan_config, generic_pwm_fan
-from feeph.emc2101.pwm import DeviceConfig, Emc2101_PWM, ExternalTemperatureSensorConfig, FanSpeedUnit, PinSixMode, TemperatureLimitType, emc2101_default_config, ets_2n3904, ets_2n3906
+from feeph.emc2101.pwm import DeviceConfig, Emc2101_PWM, FanSpeedUnit, PinSixMode, emc2101_default_config

feeph/emc2101/calibration.py

@@ -27,8 +27,9 @@ def calibrate_pwm_fan(i2c_bus: busio.I2C, model: str, pwm_frequency: int = 22500
     LH.info("Calibrating fan parameters.")
     pwm_d, pwm_f = feeph.emc2101.utilities.calculate_pwm_factors(pwm_frequency=pwm_frequency)
     steps_list = list(range(pwm_f * 2))
-    emc2101 = feeph.emc2101.core.Emc2101_core(i2c_bus=i2c_bus)
-    emc2101.configure_pin_six_as_tacho()
+    # tacho signal on pin 6, device uses PWM control
+    config = feeph.emc2101.core.ConfigRegister(alt_tach=True, dac=False)
+    emc2101 = feeph.emc2101.core.Emc2101(i2c_bus=i2c_bus, config=config)
     emc2101.configure_pwm_control(pwm_d=pwm_d, pwm_f=pwm_f, step_max=max(steps_list))
     # -----------------------------------------------------------------
     LH.debug("Disabling gradual speed rampup.")

feeph/emc2101/config_register.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env
+
+from attrs import define
+
+
+@define(eq=True)
+class ConfigRegister:
+    """
+    a representation of the EMC2101's config register (0x03)
+
+    this is not the entire configuration, there are additional registers
+    which configure different aspects of this chip, e.g. fan configuration
+    register (0x4A)
+
+    for an exhaustive description refer to EMC2101 datasheet section 6.5
+    """
+    # the comment describes what happens if the value is set to True
+    mask:        bool = False  # disable ALERT/TACH when in interrupt mode
+    standby:     bool = False  # enable low power standby mode
+    fan_standby: bool = False  # disable fan output while in standby
+    dac:         bool = False  # enable DAC output on FAN pin
+    dis_to:      bool = False  # disable SMBUS timeout
+    alt_tach:    bool = False  # configure pin six as tacho input
+    trcit_ovrd:  bool = False  # unlock tcrit limit and allow one-time write
+    queue:       bool = False  # alert after 3 critical temperature readings
+
+    def as_int(self):
+        """
+        compute the config register's value
+        """
+        config = 0x00
+        if self.mask:
+            config |= 0b1000_0000
+        if self.standby:
+            config |= 0b0100_0000
+        if self.fan_standby:
+            config |= 0b0010_0000
+        if self.dac:
+            config |= 0b0001_0000
+        if self.dis_to:
+            config |= 0b0000_1000
+        if self.alt_tach:
+            config |= 0b0000_0100
+        if self.trcit_ovrd:
+            config |= 0b0000_0010
+        if self.queue:
+            config |= 0b0000_0001
+        return config
+
+
+def parse_config_register(value: int) -> ConfigRegister:
+    """
+    parse the config register's value
+    """
+    params = dict()
+    if value & 0b1000_0000:
+        params['mask'] = True
+    if value & 0b0100_0000:
+        params['standby'] = True
+    if value & 0b0010_0000:
+        params['fan_standby'] = True
+    if value & 0b0001_0000:
+        params['dac'] = True
+    if value & 0b0000_1000:
+        params['dis_to'] = True
+    if value & 0b0000_0100:
+        params['alt_tach'] = True
+    if value & 0b0000_0010:
+        params['trcit_ovrd'] = True
+    if value & 0b0000_0001:
+        params['queue'] = True
+    return ConfigRegister(**params)