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Communications Port Programming Interface (CPPI) 4.1 DMA
20.4.3.2 Free Descriptor Queue (Receive Submit Queue)
Receive endpoints/channels use queues, referred to as free descriptor queues, or receive submit
queues, to forward completed receive packets to the host. The entries on the free descriptor queues
have pre-attached empty buffers whose size and location are described in the original buffer
information fields in the descriptor. The host is required to allocate both the descriptor and buffer and
pre-link them prior to adding (submitting) a descriptor to one of the available free descriptor queue. The
first 32 queues (queue 0 up to queue 31) are reserved for all 30 USB0/1 (endpoints 1 to 15 of each
USB module) receive endpoints/channels to handle incoming packets to the device.
20.4.3.3 Transmit Submit Queue
Transmit ports use packet queues, referred to as transmit submit queues, to store the packets that are
waiting to be transmitted. Each transmit endpoint has dedicated queues (2 queues per port) that are
reserved exclusively for a use by a single endpoint. Multiple queues per port/channel are allocated to
facilitate quality of service (QoS) for applications that require QoS. The first 30 queues, queue 32 up to
queue 61, are allocated for USB0 transmit endpoints 1 to 15 with two queues per endpoint.queues 62
up to queue 91, are allocated for transmit USB1 endpoints 1 to 15.
20.4.3.4 Transmit Completion (Return) Queue
Transmit ports use packet queues, referred to as "transmit completion queues, to return packet
descriptors to the host after packets have been transmitted. A singe queue is reserved to be used by a
single transmit endpoint. Application s/w needs to insure that the right set of queues is used to return
the Descriptors after the completion of a packet transmission based on the endpoint number used. For
USB0 transmit endpoints 1 to 15 Queues 92 up to queue 106 are reserved/assigned for use as a
completion queue respectively. Similarly for USB1 transmit endpoints 1 to 15, queues 107 up to queue
121 is used as completion queue, respectively.
Transmit Completion Queues are also used to return packet Descriptors when performing a Transmit
channel teardown operation.
20.4.3.5 Receive Completion (Return) Queue
Receive ports use packet queues, referred to as receive completion queues, to return packet
descriptors to the port after packets have been received. A singe queue is reserved to be used by a
single receive endpoint. Application s/w needs to insure that the right set of queues is used to return the
descriptors after the completion of a packet reception based on the endpoint number used. For USB0
receive endpoints 1 to 15 queues 122 up to queue 136 are reserved/assigned for use as a receive
completion queue respectively. Similarly for USB1 receive endpoints 1 to 15, queues 137 up to queue
151 is used as completion queue respectively.
Receive channel teardown is not necessary for receive transactions and no channel teardown
information nor resource is available
20.4.3.6 Diverting Queue Packets from one Queue to Another
The host can move the entire contents of one queue to another queue by writing the source queue
number and the destination queue number to the Queue Diversion register. When diverting packets, the
descriptors are pushed onto the tail of the destination queue.
20.4.3.7 Teardown Queue
Teardown queue
20.4.4 Memory Regions and Linking RAM
In addition to allocating buffer for raw data and memory for Descriptors, the host is responsible for
allocating additional memory for exclusive use of the CPPI DMA Queue Manager to be used as a
scratch PAD RAM. The queue manager uses this memory to manage states of descriptors submitted
1806
Universal Serial Bus (USB)
Preliminary
© 2011, Texas Instruments Incorporated
www.ti.com
SPRUGX9 – 15 April 2011
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