Merge pull request #222 from nomis52/cdc

Add the CDC interface association descriptor.

Author: peternewman

firmware/src/usb_descriptors.c

@@ -79,9 +79,12 @@ static const USB_DEVICE_DESCRIPTOR g_device_descriptor = {
   0x12,  // Size of this descriptor in bytes
   USB_DESCRIPTOR_DEVICE,  // DEVICE descriptor type
   0x0200,  // USB Spec Release Number in BCD format
-  0x00,  // Class Code
-  0x00,  // Subclass code
-  0x00,  // Protocol code
+  // Since we use an Interface Association, we need to set the class, subclass
+  // and protocol according to:
+  // https://msdn.microsoft.com/en-us/library/windows/hardware/ff540054(v=vs.85).aspx
+  0xef,  // Class Code
+  0x02,  // Subclass code
+  0x01,  // Protocol code
   USB_DEVICE_EP0_BUFFER_SIZE,  // Max packet size for EP0, see usb_config.h
   USB_DEVICE_VENDOR_ID,
   USB_DEVICE_MAIN_PRODUCT_ID,
@@ -98,13 +101,23 @@ static const uint8_t g_config_descriptor[] = {
   // Configuration Descriptor Header
   0x09,  // Size of this descriptor
   USB_DESCRIPTOR_CONFIGURATION,  // Descriptor type
-  0x6c, 0x00,  // Total length of data for this cfg
+  0x74, 0x00,  // Total length of data for this cfg
   4,  // Number of interfaces in this cfg
   1,  // Index value of this configuration
   0,  // Configuration string index
   USB_ATTRIBUTE_DEFAULT | USB_ATTRIBUTE_SELF_POWERED,  // Attributes
   USB_POWER_CONSUMPTION,  // Max power consumption
 
+  // Interface Association Descriptor: CDC Function 1
+  0x08,   // Size of this descriptor in bytes
+  0x0B,   // Interface association descriptor type
+  0,   // The first associated interface
+  0x02,   // Number of contiguous associated interfaces
+  0x02,   // bInterfaceClass of the first interface
+  0x02,   // bInterfaceSubclass of the first interface
+  0x01,   // bInterfaceProtocol of the first interface
+  0x00,   // Interface string index
+
   // First CDC Interface Descriptor
   0x09,  // Size of this descriptor in bytes
   USB_DESCRIPTOR_INTERFACE,  // Descriptor type