USBx_CLK_RECOVER_INT_STATUS field descriptions
Field
Description
7–5
Reserved
This field is reserved.
Should always be written as 0.
4
OVF_ERROR
Indicates that the USB clock recovery algorithm has detected that the frequency trim adjustment needed
for the IRC48M output clock is outside the available TRIM_FINE adjustment range for the IRC48M
module.
0
No interrupt is reported
1
Unmasked interrupt has been generated
3–0
Reserved
This field is reserved.
Should always be written as 0.
42.5 OTG and Host mode operation
The Host mode logic allows devices such as digital cameras and palmtop computers to
function as a USB Host Controller. The OTG logic adds an interface to allow the OTG
Host Negotiation and Session Request Protocols (HNP and SRP) to be implemented in
software. Host Mode allows a peripheral such as a digital camera to be connected directly
to a USB compliant printer. Digital photos can then be easily printed without being
uploaded to a PC. In the palmtop computer application, a USB compliant keyboard/
mouse can be connected to the palmtop computer with the obvious advantages of easier
interaction.
Host mode is intended for use in handheld-portable devices to allow easy connection to
simple HID class devices such as printers and keyboards. It is not intended to perform the
functions of a full OHCI or UHCI compatible host controller found on PC motherboards.
The USB-FS is not supported by Windows as a USB host controller. Host mode allows
bulk, isochronous, interrupt and control transfers. Bulk data transfers are performed at
nearly the full USB interface bandwidth. Support is provided for ISO transfers, but the
number of ISO streams that can be practically supported is affected by the interrupt
latency of the processor servicing the Token Done interrupts from the SIE. Custom
drivers must be written to support Host mode operation.
Setting the HOST_MODE_EN bit in the CTL register enables Host mode. The USB-FS
core can only operate as a peripheral device or in Host mode. It cannot operate in both
modes simultaneously. When HOST_MODE is enabled, only endpoint zero is used. All
other endpoints should be disabled by software.
Chapter 42 Universal Serial Bus Full Speed OTG Controller (USBFSOTG)
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
Freescale Semiconductor, Inc.
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