try to set correct f_clock before raising exception

Author: zariiii9003

can/interfaces/pcan/pcan.py

@@ -258,19 +258,27 @@ def __init__(
             raise ValueError("BusState must be Active or Passive")
 
         if isinstance(timing, BitTimingFd):
-            valid_fd_clocks = [
-                20000000,
-                24000000,
-                30000000,
-                40000000,
-                60000000,
-                80000000,
+            valid_fd_f_clocks = [
+                20_000_000,
+                24_000_000,
+                30_000_000,
+                40_000_000,
+                60_000_000,
+                80_000_000,
             ]
-            if timing.f_clock not in valid_fd_clocks:
-                raise CanInitializationError(
-                    f"The PcanBus requires one of the following CAN clocks for CAN FD: "
-                    f"{','.join([str(f) for f in valid_fd_clocks])} (timing={timing!r})"
-                )
+            if timing.f_clock not in valid_fd_f_clocks:
+                # try setting a valid f_clock. Raise exception if this fails
+                for f_clock in reversed(valid_fd_f_clocks):
+                    try:
+                        timing = BitTimingFd(**{**timing, "f_clock": f_clock})
+                        break
+                    except ValueError:
+                        continue
+                else:
+                    raise CanInitializationError(
+                        f"The PcanBus requires one of the following CAN clocks for CAN FD: "
+                        f"{','.join([str(f) for f in valid_fd_f_clocks])} (timing={timing!r})"
+                    )
             self.fd_bitrate = (
                 f"f_clock={timing.f_clock},"
                 f"nom_brp={timing.nom_brp},"
@@ -287,9 +295,13 @@ def __init__(
             )
         elif isinstance(timing, BitTiming):
             if timing.f_clock != 8_000_000:
-                raise CanInitializationError(
-                    f"The PcanBus requires a 8MHz CAN clock for CAN2.0 (timing={timing!r})"
-                )
+                try:
+                    # try different prescaler values
+                    timing = BitTiming(**{**timing, "f_clock": 8_000_000})
+                except ValueError:
+                    raise CanInitializationError(
+                        f"The PcanBus requires a 8MHz CAN clock for CAN2.0 (timing={timing!r})"
+                    ) from None
             pcan_bitrate = TPCANBaudrate(timing.btr0 << 8 | timing.btr1)
             result = self.m_objPCANBasic.Initialize(
                 self.m_PcanHandle, pcan_bitrate, hwtype, ioport, interrupt