USB Host External Hub Driver (Ext Hub)
Introduction
The External Hub Driver (henceforth referred to as Ext Hub Driver)
Requirements
USB Specification Requirements
Chapter 11 of the USB 2.0 specification outlines some aspects, when a USB Hub device is attached to a powered port.
The design of the Ext Driver takes into consideration the following:
Connectivity behavior
Power management
Device connect/disconnect detection
Bus fault detection and recovery
High-, full-, and low-speed device support
Note
For more detailed information, please refer to USB 2.0 Specification > Chapter 11.1 Overview.
Host Stack Requirements
In addition to the USB 2.0 specification requirements, the Ext Hub Driver also takes into consideration the requirements set for the overall Host Stack (see USB Host Maintainers Notes (Design Guidelines)):
Ext Hub Driver must not instantiate any tasks/threads
Ext Hub Driver must be event driven, providing event callbacks and an event processing function
Ext Hub Driver must use only API from underlying layer (USBH)
Implementation & Usage
Host Stack Interaction
The Ext Hub Driver takes place between USB Host layer and USBH layer, next to the Hub Driver. The Hub Driver and the Ext Hub Driver were split into two Drivers to achieve the goal of logic distinguishing between root Hub and external Hub.
Device handling
The Ext Hub Driver can be installed via ext_hub_install() call and uninstalled via ext_hub_uninstall() call. After installation the Ext Hub provides the following APIs for external Hub addition and removal:
ext_hub_new_dev()which will verify the device class (HUB_CLASSCODE (09H)) and, if the device has the Hub class, the Ext Hub Driver:allocates a new device object
adds it to the external device pool
starts the process of Hub configuration (retrieving Hub Descriptor, Device status and Hub status)
ext_hub_dev_gone()which will verify the device in the Ext Hub Driver list and start the process of external Hub device removing.
Events & Processing
The Ext Hub Driver is completely event driven and all event handling is done via the ext_hub_process() function. The ext_hub_config_t.proc_req_cb callback provided on the Ext Hub Driver installation will be called when processing is required. Typically, ext_hub_process() will be called from the Hub Driver hub_process() processing function.
The Ext Hub Driver does not expose any event callback.