Remove BCD.Int, add BCD.Major/Minor. Remove USB spec versions

- I don't expect them to get much use, and reuse of BCD for USB spec
version and device revision makes it somewhat confusing.

usb/error.go

@@ -76,6 +76,7 @@ var errorString = map[Error]string{
 // TransferStatus contains information about the result of a transfer.
 type TransferStatus uint8
 
+// Transfer status values provided by libusb.
 const (
 	TransferCompleted TransferStatus = C.LIBUSB_TRANSFER_COMPLETED
 	TransferError     TransferStatus = C.LIBUSB_TRANSFER_ERROR

usb/fakelibusb_test.go

@@ -30,8 +30,8 @@ var (
 		&Descriptor{
 			Bus:      1,
 			Address:  1,
-			Spec:     USB_2_0,
+			Spec:     Version(2, 0),
-			Device:   BCD(0x0100), // 1.00
+			Device:   Version(1, 0),
 			Vendor:   ID(0x9999),
 			Product:  ID(0x0001),
 			Protocol: 255,
@@ -66,8 +66,8 @@ var (
 		&Descriptor{
 			Bus:      1,
 			Address:  2,
-			Spec:     USB_2_0,
+			Spec:     Version(2, 0),
-			Device:   BCD(0x0103), // 1.03
+			Device:   Version(1, 3),
 			Vendor:   ID(0x8888),
 			Product:  ID(0x0002),
 			Protocol: 255,

usb/libusb.go

@@ -420,8 +420,8 @@ var (
 	libusbIsoOffset = unsafe.Offsetof(C.struct_libusb_transfer{}.iso_packet_desc)
 )
 
-//export xfer_callback
+//export xferCallback
-func xfer_callback(cptr unsafe.Pointer) {
+func xferCallback(cptr unsafe.Pointer) {
 	ch := *(*chan struct{})(cptr)
 	close(ch)
 }

usb/misc.go

@@ -19,30 +19,39 @@ import (
 	"fmt"
 )
 
+// BCD is a binary-coded decimal version number, with first 8 bits representing
+// the major version number, an latter 8 bits the minor version number.
+// Major and minor are composed of 4+4 bits, where each 4 bits represents
+// a decimal digit.
+// Example: BCD(0x1234) means major 12 (decimal) and minor 34 (decimal).
 type BCD uint16
 
-const (
+// Major is the major number of the BCD.
-	USB_2_0 BCD = 0x0200
+func (s BCD) Major() uint8 {
-	USB_1_1 BCD = 0x0110
+	maj := uint8(s >> 8)
-	USB_1_0 BCD = 0x0100
+	return 10*(maj>>4) + maj&0x0f
-)
-
-func (d BCD) Int() (i int) {
-	ten := 1
-	for o := uint(0); o < 4; o++ {
-		n := ((0xF << (o * 4)) & d) >> (o * 4)
-		i += int(n) * ten
-		ten *= 10
-	}
-	return
 }
 
-func (d BCD) String() string {
+// Minor is the minor number of the BCD.
-	return fmt.Sprintf("%02x.%02x", int(d>>8), int(d&0xFF))
+func (s BCD) Minor() uint8 {
+	min := uint8(s & 0xff)
+	return 10*(min>>4) + min&0x0f
 }
 
+// String returns a dotted representation of the BCD (major.minor).
+func (s BCD) String() string {
+	return fmt.Sprintf("%d.%02d", s.Major(), s.Minor())
+}
+
+// Version returns a BCD version number with given major/minor.
+func Version(major, minor uint8) BCD {
+	return (BCD(major)/10)<<12 | (BCD(major)%10)<<8 | (BCD(minor)/10)<<4 | BCD(minor)%10
+}
+
+// ID represents a vendor or product ID.
 type ID uint16
 
+// String returns a hexadecimal ID.
 func (id ID) String() string {
 	return fmt.Sprintf("%04x", int(id))
 }

usb/misc_test.go

@@ -21,19 +21,22 @@ import (
 
 func TestBCD(t *testing.T) {
 	tests := []struct {
-		BCD
+		major, minor uint8
-		Int int
+		bcd          BCD
-		Str string
+		str          string
 	}{
-		{0x1234, 1234, "12.34"},
+		{1, 1, 0x0101, "1.01"},
+		{12, 34, 0x1234, "12.34"},
 	}
 
 	for _, test := range tests {
-		if got, want := test.BCD.Int(), test.Int; got != want {
+		bcd := Version(test.major, test.minor)
-			t.Errorf("Int(%x) = %d, want %d", test.BCD, got, want)
+		if bcd != test.bcd {
+			t.Errorf("Version(%d, %d): got BCD %04x, want %04x", test.major, test.minor, uint16(bcd), uint16(test.bcd))
+			continue
 		}
-		if got, want := test.BCD.String(), test.Str; got != want {
+		if got, want := bcd.String(), test.str; got != want {
-			t.Errorf("String(%x) = %q, want %q", test.BCD, got, want)
+			t.Errorf("String(%04x) = %q, want %q", uint16(test.bcd), got, want)
 		}
 	}
 }

usb/transfer.c

@@ -18,10 +18,10 @@
 #include <string.h>
 
 void print_xfer(struct libusb_transfer *xfer);
-void xfer_callback(void *);
+void xferCallback(void *);
 
 void callback(struct libusb_transfer *xfer) {
-	xfer_callback(xfer->user_data);
+	xferCallback(xfer->user_data);
 }
 
 int submit(struct libusb_transfer *xfer) {