LM3S5652 Datasheet, PDF (663/848 Pages) Texas Instruments – Stellaris® LM3S5652 Microcontroller

Stellaris® LM3S5652 Microcontroller
When configuring the size of the FIFOs for endpoints, take into account the maximum packet size
for an endpoint.
■ Bulk. Bulk endpoints should be the size of the maximum packet (up to 64 bytes) or twice the
maximum packet size if double buffering is used (described further in the following section).
■ Interrupt. Interrupt endpoints should be the size of the maximum packet (up to 64 bytes) or twice
the maximum packet size if double buffering is used.
■ Isochronous. Isochronous endpoints are more flexible and can be up to 1023 bytes.
■ Control. It is also possible to specify a separate control endpoint for a USB Device. However,
in most cases the USB Device should use the dedicated control endpoint on the USB controller’s
endpoint 0.
17.3.1.1
Endpoints
When operating as a Device, the USB controller provides two dedicated control endpoints (IN and
OUT) and six configurable endpoints (3 IN and 3 OUT) that can be used for communications with
a Host controller. The endpoint number and direction associated with an endpoint is directly related
to its register designation. For example, when the Host is transmitting to endpoint 1, all configuration
and data is in the endpoint 1 transmit register interface.
Endpoint 0 is a dedicated control endpoint used for all control transactions to endpoint 0 during
enumeration or when any other control requests are made to endpoint 0. Endpoint 0 uses the first
64 bytes of the USB controller's FIFO RAM as a shared memory for both IN and OUT transactions.
The remaining six endpoints can be configured as control, bulk, interrupt, or isochronous endpoints.
They should be treated as three configurable IN and three configurable OUT endpoints. The endpoint
pairs are not required to have the same type for their IN and OUT endpoint configuration. For
example, the OUT portion of an endpoint pair could be a bulk endpoint, while the IN portion of that
endpoint pair could be an interrupt endpoint. The address and size of the FIFOs attached to each
endpoint can be modified to fit the application's needs.
17.3.1.2
IN Transactions as a Device
When operating as a USB Device, data for IN transactions is handled through the FIFOs attached
to the transmit endpoints. The sizes of the FIFOs for the three configurable IN endpoints are
determined by the USB Transmit FIFO Start Address (USBTXFIFOADD) register. The maximum
size of a data packet that may be placed in a transmit endpoint’s FIFO for transmission is
programmable and is determined by the value written to the USB Maximum Transmit Data Endpoint
n (USBTXMAXPn) register for that endpoint. The endpoint’s FIFO can also be configured to use
double-packet or single-packet buffering. When double-packet buffering is enabled, two data packets
can be buffered in the FIFO, which also requires that the FIFO is at least two packets in size. When
double-packet buffering is disabled, only one packet can be buffered, even if the packet size is less
than half the FIFO size.
Note: The maximum packet size set for any endpoint must not exceed the FIFO size. The
USBTXMAXPn register should not be written to while data is in the FIFO as unexpected
results may occur.
Single-Packet Buffering
If the size of the transmit endpoint's FIFO is less than twice the maximum packet size for this endpoint
(as set in the USB Transmit Dynamic FIFO Sizing (USBTXFIFOSZ) register), only one packet
can be buffered in the FIFO and single-packet buffering is required. When each packet is completely
November 17, 2011
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