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Freescale Semiconductor Electronic Components Datasheet

AN3631 Datasheet

Simplified Device Data Structures

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AN3631 pdf
Freescale Semiconductor
Application Note
Document Number: AN3631
Rev. 0, 03/2008
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Simplified Device Data
Structures for the High-End
ColdFire Family USB Modules
by: Melissa Hunter
Applications
Microcontroller Solutions Group
Some of the high-end ColdFire products (such as the
Contents
MCF532x, MCF537x, MCF5253, and MCF5445x
1 USB Device Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
devices) contain an EHCI-compatible host or
dual-role/OTG USB controller. The dual-role module
1.1 Endpoint Queue Head (dQH) . . . . . . . . . . . . . . . . . 2
1.2 Endpoint Transfer Descriptor (dTD) . . . . . . . . . . . . 4
2 USB Device Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
can be used as a USB host, a USB device, or as an
2.1 USB Device Initialization . . . . . . . . . . . . . . . . . . . . . 7
On-the-Go device. When the dual-role module is used as
3
2.2 Device Enumeration . . . . . . . . . . . . . . . . . . . . . . . . 9
Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . 13
a device, it uses data structures to control USB data
movement. These data structures are similar in some
ways to the embedded host controller interface (EHCI)
data structures that are used when operating in host
mode.
The purpose of this application note is to discuss a
simplified version of the device mode data structures
used by the dual-role USB controller. This document
also walks through a real-world example to show how
the USB controller is programmed and to provide
examples of how the data structures are used.
This document is intended as a guide for developing a
simple driver for communicating with a USB host. The
simplified version of the data structures discussed in this
© Freescale Semiconductor, Inc., 2008. All rights reserved.


Freescale Semiconductor Electronic Components Datasheet

AN3631 Datasheet

Simplified Device Data Structures

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AN3631 pdf
USB Device Overview
document do not support all of the capability of the USB controller. To simplify the data strwuwcwtu.Dreasta, Sheet4U.com
isochronous transfers are not discussed. Transfer sizes are also restricted to smaller than 4 KB. When using
the full data structures discussed in the device reference manual, both isochronous traffic and transfers
larger than 4 KB are supported.
1 USB Device Overview
For device operations, the USB module uses two different types of data structures — endpoint queue heads
(dQHs) and endpoint transfer descriptors (dTDs).
One dQH is defined for each endpoint and each direction. For example, there is one dQH used for endpoint
0 OUT transactions and a second dQH used for endpoint 0 IN transactions. These dQHs are stored in
memory as an eight element array as shown in Figure 1.
ENDPOINTLISTADDR
ENDPOINTLISTADDR + 0x040
ENDPOINTLISTADDR + 0x080
ENDPOINTLISTADDR + 0x0C0
ENDPOINTLISTADDR + 0x100
ENDPOINTLISTADDR + 0x140
ENDPOINTLISTADDR + 0x180
ENDPOINTLISTADDR + 0x1C0
Endpoint Queue Heads
Endpoint QH0 - Out
Endpoint QH0 - In
Endpoint QH1 - Out
Endpoint QH1 - In
Endpoint QH2 - Out
Endpoint QH2 - In
Endpoint QH3 - Out
Endpoint QH3 - In
Transfer Buffer
Pointer
Transfer Buffer
Pointer
Endpoint
Transfer
Descriptors
(dTDs)
Transfer
Buffer
Transfer
Buffer
Transfer
Buffer
Transfer
Buffer
Figure 1. Endpoint Queue Head Diagram
1.1 Endpoint Queue Head (dQH)
There is one dQH used for each direction of each endpoint as shown in Figure 1. The dQH defines the max
packet length along with other options for the endpoint. When a packet is transferred, the overlay area of
the dQH acts as a staging area for the dTD so the device controller can access needed information with
minimal latency.
Figure 2 shows a simplified dQH structure where the fields relating to isochronous transactions and large
transfers (transfers that require more than one buffer pointer) have been removed or set to static values.
This is a simplified version of the dQH structure specified in the device reference manual.
Simplified Device Data Structures for the High-End ColdFire Family USB Modules, Rev. 0
2 Freescale Semiconductor


Part Number AN3631
Description Simplified Device Data Structures
Maker Freescale Semiconductor
Total Page 14 Pages
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