maixbit: add board definition and dummy runtime

src/runtime/runtime_k210_baremetal.go

@@ -0,0 +1,27 @@
+// +build k210,!qemu
+
+package runtime
+
+import (
+	"device/kendryte"
+	"device/riscv"
+)
+
+var clockFrequency uint32 = kendryte.SYSCTL.CLK_FREQ.Get()
+
+// ticksToNanoseconds converts RTC ticks to nanoseconds.
+func ticksToNanoseconds(ticks timeUnit) int64 {
+	return int64(ticks) * 1e9 / clockFrequency
+}
+
+// nanosecondsToTicks converts nanoseconds to RTC ticks.
+func nanosecondsToTicks(ns int64) timeUnit {
+	return timeUnit(ns * 64 / 1953125)
+}
+
+func abort() {
+	// lock up forever
+	for {
+		riscv.Asm("wfi")
+	}
+}