rename package machine/usb2 to machine/usb

src/machine/usb/util_arm.go

@@ -0,0 +1,16 @@
+// +build arm
+
+package usb
+
+import "device/arm"
+
+// udelay waits for the given number of microseconds before returning.
+// We cannot use the sleep timer from this context (import cycle), but we need
+// an approximate method to spin CPU cycles for short periods of time.
+//go:inline
+func udelay(microsec uint32) {
+	n := cycles(microsec, descCPUFrequencyHz)
+	for i := uint32(0); i < n; i++ {
+		arm.Asm(`nop`)
+	}
+}