maixbit: support both GPIO and GPIOHS controllers

src/runtime/runtime_k210_baremetal.go

@@ -3,20 +3,21 @@
 package runtime
 
 import (
-	"device/kendryte"
 	"device/riscv"
 )
 
-var clockFrequency int64 = int64(kendryte.SYSCTL.CLK_FREQ.Get())
-
-// ticksToNanoseconds converts RTC ticks to nanoseconds.
+// ticksToNanoseconds converts CPU ticks to nanoseconds.
 func ticksToNanoseconds(ticks timeUnit) int64 {
-	return int64(ticks) * 1e9 / clockFrequency
+	// The following calculation is actually the following, but with both sides
+	// reduced to reduce the risk of overflow:
+	//     ticks * 1e9 / (390000000 / 50)
+	// 50 is the CLINT divider and 390000000 is the CPU frequency.
+	return int64(ticks) * 5000 / 39
 }
 
-// nanosecondsToTicks converts nanoseconds to RTC ticks.
+// nanosecondsToTicks converts nanoseconds to CPU ticks.
 func nanosecondsToTicks(ns int64) timeUnit {
-	return timeUnit(ns * 64 / 1953125)
+	return timeUnit(ns * 39 / 5000)
 }
 
 func abort() {