Preliminary
Architecture
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20.2 Architecture
The USB controller within the device supports 15 Transmit endpoints and 15 Receive endpoints in
addition to Endpoint 0. (The use of these endpoints for IN and OUT transactions depends on whether
the USB controller is being used as a device/peripheral or as a host. When used as a peripheral, IN
transactions are processed through TX endpoints and OUT transactions are processed through Rx
endpoints. When used as a host, IN transactions is processed through Rx endpoints and OUT
transactions is processed through TX endpoints.)
These additional endpoints can be individually configured in software to handle either Bulk transfers
(which also allows them to handle Interrupt transfers), Isochronous transfers or Control transfers.
Further, the endpoints can also be allocated to different target device functions on the fly – maximizing
the number of devices that can be simultaneously supported.
Each endpoint requires a chunk of memory allocated within the FIFO to be associated with it. The USB
module has a single block of FIFO RAM (32 Kbytes in size) to be shared by all endpoints. The FIFO for
Endpoint 0 is required to be 64 bytes deep and will buffer 1 packet. The first 64 Bytes of the FIFO RAM
is reserved by hardware for Endpoint 0 usage and for this reason user software does not need (nor has
the capability) to allocate FIFO for Endpoint 0. The rest of the FIFO RAM is user configurable with
regard to the other endpoint FIFOs, which may be from 8 to 8192 bytes in size and can buffer either 1
or 2 packets.
Separate FIFOs may be associated with each endpoint: alternatively a TX endpoint and the Rx
endpoint with the same Endpoint number can be configured to use the same FIFO, for example to
reduce the size of RAM block needed, provided they can never be active at the same time.
The role (host or device) that the USB controller assumes is chosen by user firmware programming the
respective USB controller MODE register defined within the USB subsystem space. Note that some
USB pins have not been bonded out and the functions of these pins are controlled by user software via
dedicated registers.
The user has access to the controller through the OCP slave interface via the CPU. The user can
process USB transactions entirely from the CPU or can also use the DMA to perform data transfer. The
CPPI DMA can be used to service Endpoints 1 to 15 not Endpoint 0. CPU access method is used to
service Endpoint 0 transactions.
20.2.1 Clock Control
Two main clocks are used to by the USB subsystem, the OCP clock and the UTMI/PHY clock.
The OCP clock (SYSCLK6), also referred as the System Clock, is the clock that is used to clock the
controller and all other blocks of the USB subsystem with the exception of the PHY. This clock is
controlled by the PRCM. A clock rate of 60 MHz or greater must be used to guarantee core operation
can deliver full USB 2.0 bandwidth (480 Mb/s). In other words, SYSCLK6 should not be less than 60
MHz. SYSCLK6 is derived from the main PLL.
The UTMI/PHY clock is derived from a 24 MHz clock sourced to the PHY. PHY internal PLL will derive
the necessary bit clock and 60MHz UTMI clock
20.2.2 Signal Descriptions
The USB subsystem external interface signals are displayed within
Table 20-1. USBSS Interface Signals
Pin (x=0/1)
Type
Description
USBx_DP
I/O
USBx data differential pair
USBx_DN
USBx_DRVVBUS
O
USBx VBUS supply control
USBx_VBUS
I
USBx VBUS (input only for voltage sensing)
1756Universal Serial Bus (USB)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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