did something

vendor/periph.io/x/host/v3/bcm283x/timer.go

@@ -0,0 +1,60 @@
+// Copyright 2017 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package bcm283x
+
+import (
+	"time"
+
+	"periph.io/x/host/v3/cpu"
+)
+
+// ReadTime returns the time on a monotonic 1Mhz clock (1µs resolution).
+//
+// It only works if bcm283x-dma successfully loaded. Otherwise it returns 0.
+func ReadTime() time.Duration {
+	if drvDMA.timerMemory == nil {
+		return 0
+	}
+	return (time.Duration(drvDMA.timerMemory.high)<<32 | time.Duration(drvDMA.timerMemory.low)) * time.Microsecond
+}
+
+// Nanospin spins the CPU without calling into the kernel code if possible.
+func Nanospin(t time.Duration) {
+	start := ReadTime()
+	if start == 0 {
+		// Use the slow generic version.
+		cpu.Nanospin(t)
+		return
+	}
+	// TODO(maruel): Optimize code path for sub-1µs duration.
+	for ReadTime()-start < t {
+	}
+}
+
+//
+
+const (
+	// 31:4 reserved
+	timerM3 = 1 << 3 // M3
+	timerM2 = 1 << 2 // M2
+	timerM1 = 1 << 1 // M1
+	timerM0 = 1 << 0 // M0
+)
+
+// Page 173
+type timerCtl uint32
+
+// timerMap represents the registers to access the 1Mhz timer.
+//
+// Page 172
+type timerMap struct {
+	ctl  timerCtl // CS
+	low  uint32   // CLO
+	high uint32   // CHI
+	c0   uint32   // 0
+	c1   uint32   // C1
+	c2   uint32   // C2
+	c3   uint32   // C3
+}