functioning USB-CDC class initialization

src/machine/usb/util.go

@@ -216,12 +216,33 @@ func cycles(microsec, cpuFreqHz uint32) uint32 {
 	return uint32((uint64(microsec) * uint64(cpuFreqHz)) / 1000000)
 }
 
+//go:inline
+func endpointValid(address uint8) bool {
+	return address&descEndpointInvalid == 0
+}
+
 //go:inline
 func unpackEndpoint(address uint8) (number, direction uint8) {
 	return (address & descEndptAddrNumberMsk) >> descEndptAddrNumberPos,
 		(address & descEndptAddrDirectionMsk) >> descEndptAddrDirectionPos
 }
 
+//go:inline
+func packEndpoint(number, direction uint8) (address uint8) {
+	return ((number << descEndptAddrNumberPos) & descEndptAddrNumberMsk) |
+		((direction << descEndptAddrDirectionPos) & descEndptAddrDirectionMsk)
+}
+
+//go:inline
+func endpointNumber(address uint8) (number uint8) {
+	return (address & descEndptAddrNumberMsk) >> descEndptAddrNumberPos
+}
+
+//go:inline
+func endpointDirection(address uint8) (direction uint8) {
+	return (address & descEndptAddrDirectionMsk) >> descEndptAddrDirectionPos
+}
+
 //go:inline
 func rxEndpoint(number uint8) uint8 {
 	return (number & descEndptAddrNumberMsk) | descEndptAddrDirectionOut
@@ -245,20 +266,23 @@ func indexEndpoint(index uint8) uint8 {
 }
 
 // wrap computes the index into a circular buffer of length mod by walking
-// forward n elements if n is positive, or reverse n elements if n is negative.
-// For example, both wrap(42, 10) and wrap(-308, 10) return 2.
+// forward n elements if n is positive, or reverse -n elements if n is negative.
+// For example, both wrap(12, 10) and wrap(-18, 10) return 2.
 //go:inline
 func wrap(n, mod int) int {
-	if mod <= 0 || n == mod {
+	if mod <= 0 {
+		// Buffer length (mod) must be positive.
 		return 0
 	}
 	if n < 0 {
 		if -n < mod {
+			// Do not wrap around (no underflow).
 			return mod + n
 		}
 		return mod - (-n % mod)
 	}
 	if n < mod {
+		// Do not wrap around (no overflow).
 		return n
 	}
 	return n % mod