NXP Semiconductors LPC24XX UM10237 - Manual (Page 411)

UM10237_4 © NXP B.V. 2009. All rights reserved.
User manual Rev. 04 — 26 August 2009 411 of 792
NXP Semiconductors
UM10237
Chapter 15: LPC24XX USB OTG controller
8. HNP support
This section describes the hardware support for the Host Negotiation Protocol (HNP)
provided by the OTG controller.
When two dual-role OTG devices are connected to each other, the plug inserted into the
mini-AB receptacle determines the default role of each device. The device with the mini-A
plug inserted becomes the default Host (A-device), and the device with the mini-B plug
inserted becomes the default Peripheral (B-device).
Once connected, the default Host (A-device) and the default Peripheral (B-device) can
switch Host and Peripheral roles using HNP.
The context of the OTG controller operation is shown in Figure 15–59 . Each controller
(Host, Device, or OTG) communicates with its software stack through a set of status and
control registers and interrupts. In addition, the OTG software stack communicates with
the external OTG transceiver through the I2C interface and the external transceiver
interrupt signal.
The OTG software stack is responsible for implementing the HNP state machines as
described in the On-The-Go Supplement to the USB 2.0 Specification.
The OTG controller hardware provides support for some of the state transitions in the
HNP state machines as described in the following subsections.
The USB state machines, the HNP switching, and the communications between the USB
controllers are described in more detail in the following documentation:
• USB OHCI specification
• USB OTG supplement, version 1.2
• USB 2.0 specification
• ISP1302 datasheet and usermanual