Getting descriptors and endpoints from USB
Caution: This page may contain information that is specific to the legacy version of the driver framework (DFv1).
The usb class contains several subclasses providing access to the interfaces, descriptors,
and endpoints of the usb device. The subclasses included are:
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:
DescriptorListthroughGetDescriptorList()EndpointListthroughGetEndpointList()
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());
}