The USBA 2.0 framework is not a device driver itself. This chapter describes the client drivers shown in Figure 20–1 and Figure 20–2. The client drivers interact with various kinds of USB devices such as mass storage devices, printers, and human interface devices. The hub driver is a client driver that is also a nexus driver. The hub driver enumerates devices on its ports and creates devinfo nodes for those devices and then attaches the client drivers. This chapter does not describe how to write a hub driver.
USB drivers have the same structure as any other Solaris driver. USB drivers can be block drivers, character drivers, or STREAMS drivers. USB drivers follow the calling conventions and use the data structures and routines described in the Solaris OS section 9 man pages. See Intro(9E), Intro(9F), and Intro(9S).
The difference between USB drivers and other Solaris drivers is that USB drivers call USBA 2.0 framework functions to access the device instead of directly accessing the device. The USBA 2.0 framework supplements the standard Solaris DDI routines. See the following figure.
Figure 20–2 shows interfaces in more detail than Figure 20–1 does. Figure 20–2 shows that the USBA is a kernel subsystem into which a client driver can call, just as a client driver can call DDI functions.
Not all systems have all of the host controller interfaces shown in Figure 20–2. OHCI (Open Host Controller Interface) hardware is most prevalent on SPARC systems and third-party USB PCI cards. UHCI (Universal Host Controller Interface) hardware is most prevalent on x86 systems. However, both OHCI and UHCI hardware can be used on any system. When EHCI (Enhanced Host Controller Interface) hardware is present, the EHCI hardware is on the same card and shares the same ports with either OHCI or UHCI.
The host controllers, host controller drivers, and HCDI make up a transport layer that is commanded by the USBA. You cannot directly call into the OHCI, EHCI, or UHCI. You call into them indirectly through the platform-independent USBA interface.