Getting descriptors and endpoints from USB

The usb class contains several subclasses providing access to the interfaces, descriptors, and endpoints of the usb device. The subclasses included are:

• InterfaceList
• Interface
• DescriptorList
• EndpointList

USB descriptor report all of the device's attributes. An endpoint is a specific type of descriptor that describes the terminus of a communication flow between the host and the device.

The InterfaceList class iterates over each Interface within the usb device. Each Interface then contains:

• DescriptorList through GetDescriptorList()
• EndpointList through GetEndpointList()

These methods allow access to all the descriptors and endpoints of the interface.

Note: Endpoints are still considered descriptors and therefore can also be accessible through the GetDescriptorList() method.

The hierarchy of these subclasses can be seen in Figure 1.

Figure 1

Examples

Receiving Descriptors from USB

These examples iterate through all the descriptors in a USB device. The example iterates through all of the USB Interfaces and then iterates through all the descriptors in each interface.

Note: To iterate through the endpoints instead, replace interface.getDescriptorList() with interface.getEndpointList().

Range-based for loop

std::optional<InterfaceList> interface_list;

status = InterfaceList::Create(my_client, true, &interface_list);

if (status != ZX_OK) {
    ...
}

for (auto& interface : *interface_list) {

    for (auto& descriptor : interface.GetDescriptorList()) {
        ...
    }
}

Manual for loop

std::optional<InterfaceList> interface_list;

status = InterfaceList::Create(my_client, true, &interface_list);

if (status != ZX_OK) {
    ...
}

for (auto& interface : *interface_list) {

    auto dList_itr = interface.GetDescriptorList().begin(); // or cbegin().

    do {
        ...
    } while (++dList_itr != interface.GetDescriptorList().end());
}