fix(bit-timing): support extended hardware limits

Author: timothyanderson096-ocdealcheck

can/bit_timing.py

@@ -215,7 +215,14 @@ def from_registers(
 
     @classmethod
     def iterate_from_sample_point(
-        cls, f_clock: int, bitrate: int, sample_point: float = 69.0
+        cls,
+        f_clock: int,
+        bitrate: int,
+        sample_point: float = 69.0,
+        *,
+        tseg1_max: int = 16,
+        tseg2_max: int = 8,
+        brp_max: int = 64,
     ) -> Iterator["BitTiming"]:
         """Create a :class:`~can.BitTiming` iterator with all the solutions for a sample point.
 
@@ -225,14 +232,31 @@ def iterate_from_sample_point(
             Bitrate in bit/s.
         :param int sample_point:
             The sample point value in percent.
+        :param int tseg1_max:
+            Maximum time segment 1 value supported by the CAN controller.
+        :param int tseg2_max:
+            Maximum time segment 2 value supported by the CAN controller.
+        :param int brp_max:
+            Maximum bit rate prescaler supported by the CAN controller.
         :raises ValueError:
             if the arguments are invalid.
         """
 
         if sample_point < 50.0:
             raise ValueError(f"sample_point (={sample_point}) must not be below 50%.")
 
-        for brp in range(1, 65):
+        for name, value in (
+            ("tseg1_max", tseg1_max),
+            ("tseg2_max", tseg2_max),
+            ("brp_max", brp_max),
+        ):
+            if value < 1:
+                raise ValueError(f"{name} (={value}) must be at least 1.")
+
+        if not 5_000 <= bitrate <= 1_000_000:
+            return
+
+        for brp in range(1, brp_max + 1):
             nbt = int(f_clock / (bitrate * brp))
             if nbt < 8:
                 break
@@ -248,22 +272,27 @@ def iterate_from_sample_point(
             tseg2 = nbt - tseg1 - 1
             sjw = min(tseg2, 4)
 
-            try:
-                bt = BitTiming(
-                    f_clock=f_clock,
-                    brp=brp,
-                    tseg1=tseg1,
-                    tseg2=tseg2,
-                    sjw=sjw,
-                    strict=True,
-                )
-                yield bt
-            except ValueError:
+            if tseg1 > tseg1_max or tseg2 > tseg2_max:
                 continue
 
+            yield cls(
+                f_clock=f_clock,
+                brp=brp,
+                tseg1=tseg1,
+                tseg2=tseg2,
+                sjw=sjw,
+            )
+
     @classmethod
     def from_sample_point(
-        cls, f_clock: int, bitrate: int, sample_point: float = 69.0
+        cls,
+        f_clock: int,
+        bitrate: int,
+        sample_point: float = 69.0,
+        *,
+        tseg1_max: int = 16,
+        tseg2_max: int = 8,
+        brp_max: int = 64,
     ) -> "BitTiming":
         """Create a :class:`~can.BitTiming` instance for a sample point.
 
@@ -280,6 +309,12 @@ def from_sample_point(
             Bitrate in bit/s.
         :param int sample_point:
             The sample point value in percent.
+        :param int tseg1_max:
+            Maximum time segment 1 value supported by the CAN controller.
+        :param int tseg2_max:
+            Maximum time segment 2 value supported by the CAN controller.
+        :param int brp_max:
+            Maximum bit rate prescaler supported by the CAN controller.
         :raises ValueError:
             if the arguments are invalid.
         """
@@ -288,7 +323,14 @@ def from_sample_point(
             raise ValueError(f"sample_point (={sample_point}) must not be below 50%.")
 
         possible_solutions: list[BitTiming] = list(
-            cls.iterate_from_sample_point(f_clock, bitrate, sample_point)
+            cls.iterate_from_sample_point(
+                f_clock,
+                bitrate,
+                sample_point,
+                tseg1_max=tseg1_max,
+                tseg2_max=tseg2_max,
+                brp_max=brp_max,
+            )
         )
 
         if not possible_solutions:

doc/bit_timing.rst

@@ -87,6 +87,20 @@ produce an overview of possible bit timings for your desired bit rate:
     BR: 250_000 bit/s, SP: 87.50%, BRP: 2, TSEG1: 13, TSEG2: 2, SJW: 2, BTR: 411Ch, CLK: 8MHz
     BR: 250_000 bit/s, SP: 93.75%, BRP: 2, TSEG1: 14, TSEG2: 1, SJW: 1, BTR: 010Dh, CLK: 8MHz
 
+Controller-specific maximum values can be supplied when the standard timing
+limits are too restrictive:
+
+.. code-block:: python
+
+    timing = can.BitTiming.from_sample_point(
+        f_clock=160_000_000,
+        bitrate=250_000,
+        sample_point=87.5,
+        tseg1_max=256,
+        tseg2_max=128,
+        brp_max=512,
+    )
+
 
 It is possible to specify CAN 2.0 bit timings
 using the config file:

doc/changelog.d/2083.fixed.rst

@@ -0,0 +1 @@
+Allow ``BitTiming.from_sample_point`` to find valid timings for CAN controllers with bit rate prescalers above 32.

test/test_bit_timing.py

@@ -286,6 +286,57 @@ def test_from_sample_point():
             )
 
 
+def test_from_sample_point_with_extended_hardware_limits():
+    timing = can.BitTiming.from_sample_point(
+        f_clock=160_000_000,
+        bitrate=250_000,
+        sample_point=87.5,
+    )
+
+    assert timing.bitrate == 250_000
+    assert timing.sample_point == 87.5
+    assert timing.brp == 40
+    assert timing.tseg1 == 13
+    assert timing.tseg2 == 2
+
+    extended_timing = can.BitTiming.from_sample_point(
+        f_clock=160_000_000,
+        bitrate=250_000,
+        sample_point=87.5,
+        tseg1_max=256,
+        tseg2_max=128,
+        brp_max=512,
+    )
+    assert extended_timing.brp == 4
+    assert extended_timing.tseg1 == 139
+    assert extended_timing.tseg2 == 20
+
+    with pytest.raises(ValueError, match="No suitable bit timings found"):
+        can.BitTiming.from_sample_point(
+            f_clock=160_000_000,
+            bitrate=250_000,
+            sample_point=87.5,
+            brp_max=39,
+        )
+
+    with pytest.raises(ValueError, match="No suitable bit timings found"):
+        can.BitTiming.from_sample_point(
+            f_clock=80_000_000,
+            bitrate=2_000_000,
+            sample_point=75.0,
+        )
+
+    for parameter in ("tseg1_max", "tseg2_max", "brp_max"):
+        with pytest.raises(ValueError, match=rf"{parameter} \(=0\) must be at least 1"):
+            list(
+                can.BitTiming.iterate_from_sample_point(
+                    f_clock=16_000_000,
+                    bitrate=500_000,
+                    **{parameter: 0},
+                )
+            )
+
+
 def test_iterate_from_sample_point():
     for sp in range(50, 100):
         solutions = list(