Texas Instruments OMAP36 Series, Техническое справочное руководство

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L3 interconnect
Little or big endian
L4 interconnect
Device
Slave
Master
High-speed USB OTG controller
OCP
wrapper
MUSBMHDRC
(USB2.0 controller)
Little endian
AHB
master
AHB
slave
USB Little endian
Standard
USB host
usb-036
Public Version
High-Speed USB OTG Controller
www.ti.com
Figure 22-7. High-Speed USB OTG Controller Endianess
Big-endian support in the high-speed USB OTG controller may or may not require byte-swapping in the
data path. Byte-swapping is performed based on the unit size of data. For example, if multiple bytes are
packed into one 32-bit word, these bytes must be swapped in a big-endian interconnect. On the other
hand, if the data is only a 32-bit word (for example, a 32-bit descriptor pointer in a memory buffer), the
bytes in the word must not be swapped in big-endian mode.
In the high-speed USB OTG controller, the unit size of descriptors/descriptor pointers is 32 bits and that of
the USB data is 8 bits. Four 8-bit USB data are packed to form a 32-bit word. This 32-bit data requires
byte-swapping, whereas the descriptors/descriptor pointers do not require the same.
NOTE: Byte-swapping is not required in the control path (slave interface).
The OCP master interface (a submodule within the OCP wrapper) supports big-endian conversion by
setting the OTG_BIGENDIAN[0] BIG_ENDIAN bit to 0x1.
For interconnect write transactions, the data word is swapped as shown in Table 22-7 before its output on
the interconnect master interface. In case of an interconnect read transaction, the received data is
swapped before its output on the AHB master interface of the MUSBMHDRC core. The OCP MByteEn is
swapped before the command is issued on the OCP master interface. The OCP MAddr is always aligned
to the interconnect data size (32 bits). Therefore, the OCP MAddr is always word-aligned.
Table 22-7. Interconnect Data and MByteEn in Little- and Big-Endian Modes
AHB Size AHB Start Address
OCP MByteEn OCP MByteEn OCP Data OCP Data
Unit Size of (of Offset
in Little-Endian in Big-Endian in Little-Endian in Big-Endian
Data Packed/Nonpack (Always in
Mode Mode Mode Mode
ed Data) Little-Endian Mode)
Byte Byte 0 0001 1000 xxxb0 b0xxx
Byte Byte 1 0010 0100 xxb0x xb0xx
Byte Byte 2 0100 0010 xb0xx xxb0x
Byte Byte 3 1000 0001 b0xxx xxxb0
Byte Half-word 0 0011 1100 xxb1b0 b0b1xx
3224High-Speed USB Host Subsystem and High-Speed USB OTG Controller SWPU177N – December 2009 – Revised November 2010
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