Decouple hardware specific code from generic, agnostic code

src/avclan/timing.h

@@ -0,0 +1,32 @@
+#ifndef _TIMING_HPP_
+#define _TIMING_HPP_
+
+// Physical AVC-LAN bit-phase durations, in microseconds. These are protocol
+// facts (the bus spec), independent of any particular hardware. The active
+// target provides TICK_US — the wall-clock duration, in microseconds, of one
+// tick of whatever free-running timer it uses to measure/generate bus bits — so
+// each constant below resolves to a count of that target's ticks.
+//
+// Kept as #defines (not constexpr): no target is guaranteed to want these as a
+// specific integer width, so leave the type to the use site / target.
+
+#ifndef TICK_US
+  #error                                                                       \
+      "target must define TICK_US (microseconds per bus-timer tick) before including timing.h"
+#endif
+
+// Measured at ±0.02 μs @ F_CPU=20MHz, TCB_CLKSEL=TCB_CLKSEL_CLKDIV1_gc
+#define AVCLAN_STARTBIT_LOGIC_0 (169.0 / TICK_US)
+#define AVCLAN_STARTBIT_LOGIC_1 (20.6 / TICK_US)
+
+#define AVCLAN_BIT1_LOGIC_0 (19.7 / TICK_US)
+#define AVCLAN_BIT1_LOGIC_1 (18.1 / TICK_US)
+
+#define AVCLAN_BIT0_LOGIC_0 (32.85 / TICK_US)
+#define AVCLAN_BIT0_LOGIC_1 (6.2 / TICK_US)
+
+#define AVCLAN_READBIT_THRESHOLD (26.0 / TICK_US)
+
+#define AVCLAN_BIT_LENGTH_MAX (39.1 / TICK_US)
+
+#endif