Enhanced Host Controller Interface
Introduction
EHCI (Enhanced Host Controller Interface) is the Single method of interfacing with USB 2.0.
This makes life a lot easier than with USB 1.0, where 2 incompatible standards both survived.
This is because the USB-IF insisted on a single implementation, produced by Intel.
Interface
On a PC you will normally find the EHCI USB controller on the PCI bus - in fact it is the only access method specified in the specification.
USB 2.0 supports interfacing with USB 1.0 devices. However, EHCI is NOT expected to support them. Instead, you will find an UHCI or OHCI companion controller.
Therefore you must implement OHCI and UHCI as well. Note there are NOT companions of both types, it is one type or another.
The EHCI controller will always have a PCI Class ID of 0x0C, a Subclass ID of 0x03, and an Interface value of 0x20. These values can be used to find the configuration space of the controller, which contains the memory mapped address of the EHCI registers. The address information can be found in the BAR0 PCI configuration space register.
Registers
| Offset (Hex) | Name | Description |
|---|---|---|
| 00 | USBCMD | USB Command |
| 04 | USBSTS | USB Status |
| 08 | USBINTR | USB Interrupt Enable |
| 0C | FRINDEX | USB Frame Index |
| 10 | CTRLDSSEGMENT | 4G Segment Selector |
| 14 | PERIODICLISTBASE | Frame List Base Address |
| 18 | ASYNCLISTADDR | Next Asynchronous List Address |
| 40 | CONFIGFLAG | Configured Flag Register |