USB initialization
Internal USB driver setup
USB Connect
USB cable attached?
HW setup for UTMI mode
No
Yes
Fail VBUS
Functional Description
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• USB will operate only in device-powered mode.
• Integrated transceiver (through UTMI).
• The enumeration default timeout is 3s (USB timeout).
• ROM code uses the default value of DATAPOLARITY.
Even though using an OTG capable hardware, the ROM Code does not handle any OTG specific feature.
26.1.8.6.1.1 Overview
In case of boot from USB is chosen by the SYSBOOT pin configuration:
• The USBOTGHS hardware and PRCM clocks are configured for UTMI mode.
• The ROM Code continues with the USB procedure only if the USB cable is detected present (i.e.
VBUS is detected at transceiver level and communicated as such through the UTPI traffic). If not, the
initialization procedure is aborted.
• The ROM code implements the RNDIS class driver.
• From a user's perspective, USB boot is indistinguishable from Ethernet boot.
• The USB initialization procedure is shown in Figure 26-24.
Figure 26-24. USB Initialization Procedure
26.1.8.6.1.2 Enumeration Descriptors
The device descriptor parameters which are used during enumeration are listed in Table 26-37. The
default Vendor ID and Product ID can be automatically overridden by the customer by programming the
Efuses that are used to store these values.
Table 26-37. Customized Descriptor Parameters
Parameter Size [bytes] TI Default Values
Device ID code 2 0000h
Device Class 1 02h
Device Sub-Class 1 00h
Device Protocol 1 00h
Manufacturer String “Texas Instruments”
Product
(1)
String AM335x USB
Serial number 1 0h
(1)
See Section 1.2, Silicon Revision Functional Differences and Enhancements, for differences in operation based on AM335x
silicon revision.
4148
Initialization SPRUH73H–October 2011–Revised April 2013
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