cores.mech: Add Endless Potentiometer Decoder (WIP)

Author: Jean THOMAS

lambdalib/cores/mech/endless_potentiometer.py

@@ -0,0 +1,217 @@
+# Endless potentiometer decoding into relative rotation
+# 2025 - LambdaConcept <[email protected]>
+from amaranth import *
+from ...interface import stream
+
+__all__ = ["EndlessPotentiometerDecoder"]
+
+
+class _ThresholdDetector(Elaboratable):
+    """Detects when a value changes above/below a threshold"""
+    def __init__(self, width, threshold):
+        self._width = width
+        self._threshold = threshold
+
+        self.readout = stream.Endpoint([
+            ("value", width),
+            ("previous_value", width),
+        ])
+
+        self.detection = stream.Endpoint([
+            ("up", 1),
+            ("down", 1),
+            ("value", width),  # Readout value passthrough
+            ("delta", signed(width + 1)),  # value - previous_value
+        ])
+
+    def elaborate(self, platform):
+        m = Module()
+
+        low_threshold = Signal(signed(self._width + 1))
+        high_threshold = Signal(signed(self._width + 1))
+        m.d.comb += [
+            low_threshold.eq(self.readout.previous_value - self._threshold),
+            high_threshold.eq(self.readout.previous_value + self._threshold),
+        ]
+
+        with m.If(self.detection.ready | ~self.detection.valid):
+            m.d.sync += [
+                self.detection.valid.eq(self.readout.valid),
+                self.detection.up.eq(self.readout.value > high_threshold),
+                self.detection.down.eq(self.readout.value < low_threshold),
+                self.detection.value.eq(self.readout.value),
+                self.detection.delta.eq(self.readout.value - self.readout.previous_value),
+            ]
+        m.d.comb += self.readout.ready.eq(self.detection.ready | ~self.detection.valid)
+
+        return m
+
+
+class _DirectionDecoding(Elaboratable):
+    def __init__(self, width):
+        self._width = width
+
+        self.dir_a = stream.Endpoint([
+            ("up", 1),
+            ("down", 1),
+            ("value", width),
+            ("delta", signed(width + 1)),
+        ])
+        self.dir_b = stream.Endpoint([
+            ("up", 1),
+            ("down", 1),
+            ("value", width),
+            ("delta", signed(width + 1)),
+        ])
+
+        self.direction = stream.Endpoint([
+            ("clockwise", 1),
+            ("counterclockwise", 1),
+            ("value_a", width),
+            ("delta_a", signed(width + 1)),
+            ("value_b", width),
+            ("delta_b", signed(width + 1)),
+        ])
+
+    def elaborate(self, platform):
+        m = Module()
+
+        m.d.comb += [
+            self.dir_a.ready.eq(self.direction.ready & self.dir_b.valid),
+            self.dir_b.ready.eq(self.direction.ready & self.dir_a.valid),
+        ]
+
+        m.d.sync += [
+            self.direction.valid.eq(self.dir_a.valid & self.dir_b.valid),
+            self.direction.value_a.eq(self.dir_a.value),
+            self.direction.value_b.eq(self.dir_b.value),
+            self.direction.delta_a.eq(self.dir_a.delta),
+            self.direction.delta_b.eq(self.dir_b.delta),
+        ]
+
+        a_above_b = Signal()
+        a_above_mid = Signal()
+        b_above_mid = Signal()
+        m.d.comb += [
+            a_above_b.eq(self.dir_a.value > self.dir_b.value),
+            a_above_mid.eq(self.dir_a.value > (1 << self._width) // 2),
+            b_above_mid.eq(self.dir_b.value > (1 << self._width) // 2),
+        ]
+
+        with m.If(self.dir_a.down & self.dir_b.down):
+            with m.If(a_above_b):
+                m.d.sync += self.direction.clockwise.eq(1)
+            with m.Else():
+                m.d.sync += self.direction.counterclockwise.eq(1)
+        with m.Elif(self.dir_a.up & self.dir_b.up):
+            with m.If(~a_above_b):
+                m.d.sync += self.direction.clockwise.eq(1)
+            with m.Else():
+                m.d.sync += self.direction.counterclockwise.eq(1)
+        with m.Elif(self.dir_a.up & self.dir_b.down):
+            with m.If(a_above_mid | b_above_mid):
+                m.d.sync += self.direction.clockwise.eq(1)
+            with m.Else():
+                m.d.sync += self.direction.counterclockwise.eq(1)
+        with m.Elif(self.dir_a.down & self.dir_b.up):
+            with m.If(~a_above_mid | ~b_above_mid):
+                m.d.sync += self.direction.clockwise.eq(1)
+            with m.Else():
+                m.d.sync += self.direction.counterclockwise.eq(1)
+        with m.Else():
+            m.d.sync += [
+                self.direction.clockwise.eq(0),
+                self.direction.counterclockwise.eq(0),
+            ]
+
+        return m
+
+
+class _ReadoutDeadzoneMuxer(Elaboratable):
+    def __init__(self, width, deadzone=0.8):
+        self._width = width
+        self._deadzone = deadzone
+
+        self.direction = stream.Endpoint([
+            ("clockwise", 1),
+            ("counterclockwise", 1),
+            ("value_a", width),
+            ("delta_a", signed(width + 1)),
+            ("value_b", width),
+            ("delta_b", signed(width + 1)),
+        ])
+
+        self.position = stream.Endpoint([
+            ("diff", signed(width + 1)),
+        ])
+
+    def elaborate(self, platform):
+        m = Module()
+
+        deadzone_max = int((1 << self._width) * self._deadzone)
+        deadzone_min = int((1 << self._width) * (1 - self._deadzone))
+
+        value = Signal(signed(self._width + 1))
+        with m.If((self.direction.value_a < deadzone_max) & (self.direction.value_a > deadzone_min)):
+            with m.If(self.direction.clockwise):
+                m.d.comb += value.eq(abs(self.direction.delta_a))
+            with m.Elif(self.direction.counterclockwise):
+                m.d.comb += value.eq(-abs(self.direction.delta_a))
+            with m.Else():
+                m.d.comb += value.eq(0)
+        with m.Else():
+            with m.If(self.direction.clockwise):
+                m.d.comb += value.eq(abs(self.direction.delta_b))
+            with m.Elif(self.direction.counterclockwise):
+                m.d.comb += value.eq(-abs(self.direction.delta_b))
+            with m.Else():
+                m.d.comb += value.eq(0)
+
+        with m.If(self.position.ready | ~self.position.valid):
+            m.d.sync += [
+                self.position.valid.eq(self.direction.valid),
+                self.position.diff.eq(value),
+            ]
+        m.d.comb += self.direction.ready.eq(self.position.ready | ~self.position.valid)
+
+        return m
+
+
+class EndlessPotentiometerDecoder(Elaboratable):
+    def __init__(self, width, threshold, deadzone):
+        self._width = width
+        self._threshold = threshold
+        self._deadzone = deadzone
+
+        self.ch_a = stream.Endpoint([
+            ("value", width),
+            ("previous_value", width),
+        ])
+        self.ch_b = stream.Endpoint([
+            ("value", width),
+            ("previous_value", width),
+        ])
+
+        self.position = stream.Endpoint([
+            ("diff", signed(width + 1)),
+        ])
+
+    def elaborate(self, platform):
+        m = Module()
+
+        m.submodules.thres_det_a = thres_det_a = _ThresholdDetector(self._width, self._threshold)
+        m.submodules.thres_det_b = thres_det_b = _ThresholdDetector(self._width, self._threshold)
+        m.submodules.dir_decoding = dir_decoding = _DirectionDecoding(self._width)
+        m.submodules.deadzone_mux = deadzone_mux = _ReadoutDeadzoneMuxer(self._width, self._deadzone)
+        m.d.comb += [
+            self.ch_a.connect(thres_det_a.readout),
+            self.ch_b.connect(thres_det_b.readout),
+
+            thres_det_a.detection.connect(dir_decoding.dir_a),
+            thres_det_b.detection.connect(dir_decoding.dir_b),
+
+            dir_decoding.direction.connect(deadzone_mux.direction),
+            deadzone_mux.position.connect(self.position),
+        ]
+
+        return m

lambdalib/tests/test_cores_endless_potentiometer.py

@@ -0,0 +1,147 @@
+from amaranth.sim import *
+from lambdalib.interface.stream_sim import *
+from lambdalib.cores.mech.endless_potentiometer import (
+    EndlessPotentiometerDecoder,
+    _ThresholdDetector,
+    _DirectionDecoding,
+)
+
+
+def _wiper_to_adc(angular_position, phase_shift, adc_resolution):
+    """Emulate sampled wiper output
+
+    :param angular_position: Wiper absolute position in deg
+    :param phase_shift: Phase shift in deg
+    :param adc_resolution: ADC resolution in bits"""
+    adc_max = (1 << adc_resolution) - 1
+
+    angular_position += phase_shift
+
+    # Make it 0-180-0
+    periodic_angle = angular_position % 180
+    if (angular_position // 180) & 1:
+        periodic_angle = 180 - periodic_angle
+
+    return int(adc_max * (periodic_angle / 180))
+
+
+
+def test_wiper_to_adc():
+    # W/o phase quadrature
+    assert _wiper_to_adc(0, 0, 10) == 0
+    assert _wiper_to_adc(90, 0, 10) == 1023//2
+    assert _wiper_to_adc(180, 0, 10) == 1023
+    assert _wiper_to_adc(270, 0, 10) == 1023//2
+    assert _wiper_to_adc(360, 0, 10) == 0
+
+    # W/ phase quadrature
+    assert _wiper_to_adc(0, 90, 10) == 1023//2
+    assert _wiper_to_adc(90, 90, 10) == 1023
+    assert _wiper_to_adc(180, 90, 10) == 1023//2
+    assert _wiper_to_adc(270, 90, 10) == 0
+    assert _wiper_to_adc(360, 90, 10) == 1023//2
+
+
+def test_threshold_detector():
+    dut = _ThresholdDetector(width=8, threshold=16)
+    sim = Simulator(dut)
+
+    data = {
+        "value": [
+            0, 32, 0,
+        ],
+        "previous_value": [
+            0, 0, 32,
+        ]
+    }
+
+    tx = StreamSimSender(dut.readout, data, speed=0.3)
+    rx = StreamSimReceiver(dut.detection, length=len(data["value"]), speed=0.8, verbose=True)
+
+    sim.add_clock(1e-6)
+    sim.add_sync_process(tx.sync_process)
+    sim.add_sync_process(rx.sync_process)
+    with sim.write_vcd("tests/test_threshold_detector.vcd"):
+        sim.run()
+
+    rx.verify({
+        "up": [0, 1, 0],
+        "down": [0, 0, 1],
+        "value": [0, 32, 0],
+        "delta": [0, 32, -32],
+    })
+
+
+def test_direction_decoding():
+    dut = _DirectionDecoding(width=8)
+    sim = Simulator(dut)
+
+    ch_a = {
+        "up": [
+            1,
+        ],
+        "down": [
+            0,
+        ],
+        "value": [
+            0,
+        ],
+        "delta": [
+            0,
+        ],
+    }
+    ch_b = {
+        "up": [
+            1,
+        ],
+        "down": [
+            0,
+        ],
+        "value": [
+            0,
+        ],
+        "delta": [
+            0,
+        ],
+    }
+
+    tx_a = StreamSimSender(dut.dir_a, ch_a, speed=0.3)
+    tx_b = StreamSimSender(dut.dir_b, ch_b, speed=0.3)
+    rx = StreamSimReceiver(dut.direction, length=len(ch_a["value"]), speed=0.8, verbose=True)
+
+    sim.add_clock(1e-6)
+    sim.add_sync_process(tx_a.sync_process)
+    sim.add_sync_process(tx_b.sync_process)
+    sim.add_sync_process(rx.sync_process)
+    with sim.write_vcd("tests/test_direction_decoding.vcd"):
+        sim.run()
+
+
+def test_endless_potentiometer_decoder():
+    adc_resolution = 10  # bits
+
+    dut = EndlessPotentiometerDecoder(10, 5, 0.8)
+    sim = Simulator(dut)
+
+    wiper_a = [_wiper_to_adc(x, 0, adc_resolution) for x in range(720)]
+    wiper_b = [_wiper_to_adc(x, 90, adc_resolution) for x in range(720)]
+
+    ch_a = {
+        "value": wiper_a[:-1],
+        "previous_value": wiper_a[1:],
+    }
+    ch_b = {
+        "value": wiper_b[:-1],
+        "previous_value": wiper_b[1:],
+    }
+
+    tx_a = StreamSimSender(dut.ch_a, ch_a, speed=0.3)
+    tx_b = StreamSimSender(dut.ch_a, ch_b, speed=0.3)
+    rx = StreamSimReceiver(dut.position, length=len(ch_a["value"]), speed=0.8, verbose=True)
+
+    sim.add_clock(1e-6)
+    sim.add_sync_process(tx_a.sync_process)
+    sim.add_sync_process(tx_b.sync_process)
+    sim.add_sync_process(rx.sync_process)
+    with sim.write_vcd("tests/test_endless_potentiometer_decoder.vcd"):
+        sim.run()