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Device Initialization by ROM Code
26.4.5.2 UART
The ROM code supports booting from a UART interface with the following characteristics:
•
UART interface 3 at UART3 pins
•
Communication parameters set to 115.2 Kbps, 8 bits, even parity, 1 stop-bit
•
Two-pin interface: RX/TX with software flow control (XON/XOFF). The other UART pins are left at their
default configuration.
•
The UART wait for boot message time-out is 300 ms.
26.4.5.3 USB
The ROM code supports booting from a USB interface with the following characteristics:
•
HS USB interface
•
USB 2.0 transceiver macrocell interface (UTMI)+ low pin interface (ULPI) 8-bit data transceiver support
(single data rate)
•
TWL5030 IC detection and automatic configuration of its USB transceiver using I2C1
•
The enumeration time-out is 3 seconds.
•
The USB wait for boot message time-out is 3 seconds
The ROM code USB driver conforms with the USB 2.0 specification and the USB on-the-go (OTG)
supplement. It supports transactions at HS (that is, 480 Mbps) and FS (that is, 12 Mbps). During
peripheral booting, only the USB device functionality is used. The driver resides in the on-chip memory
(OCM) ROM, which is small. The driver therefore contains the minimum functionality needed as a USB
device and is not a full-fledged driver. It does not contain the functionality needed for a USB host. The
device functionality of the USB OTG controller is used for the peripheral booting process in the ROM
code.
HS USB peripheral booting with a cellular systems software tool (CSST) is possible with a software
development platform (SDP). The user can download CSST on
(Wireless Handset Solution >
OMAP Platform > Development Tools).
26.4.5.3.1 USB Driver Descriptors
USB devices report their attributes using descriptors. A descriptor is a data structure with a defined format.
Each descriptor begins with a byte-wide field that contains the total number of bytes in the descriptor
followed by a byte-wide field that identifies the descriptor type. Using descriptors allows concise storage of
the attributes of individual configurations so that each configuration can reuse descriptors or portions of
descriptors from other configurations that have the same characteristics. Where appropriate, descriptors
contain references to string descriptors. String descriptors contain displayable, human-readable
information that describes a descriptor. These descriptor details can be used for tool development or
debugging:
•
Device descriptor
A device descriptor contains general information about a USB device, including information that applies
globally to the device and all device configurations. A USB device has only one device descriptor.
Because the ROM code uses the HS feature of the USB core, a device-qualifier descriptor is required.
describes the device descriptors.
Table 26-15. Device Descriptor
Field
Value
Description
bLength
0x12
Size of this descriptor in bytes
bDescriptorType
0x01
Device descriptor type
bcdUSB
0x0210
USB specification release number in
binary coded decimal (BCD) format
bDeviceClass
Vendor-specific (0xFF)
Class code
bDeviceSubClass
Vendor-specific (0xFF)
Subclass code
bDeviceProtocol
Vendor-specific (0xFF)
Protocol code
bMaxPacketSize0
0x40
Maximum packet size for endpoint 0
3535
SWPU177N – December 2009 – Revised November 2010
Initialization
Copyright © 2009–2010, Texas Instruments Incorporated
