LM3S3N26 Datasheet, PDF (727/877 Pages) Texas Instruments – Stellaris® LM3S3N26 Microcontroller

Stellaris^® LM3S3N26 Microcontroller
16.4
16.4.1
Table 16-2. Remainder (MAXLOAD/4)
Value
0
1
2
3
Description
MAXLOAD = 64 bytes
MAXLOAD = 61 bytes
MAXLOAD = 62 bytes
MAXLOAD = 63 bytes
Table 16-3. Actual Bytes Read
Value
0
1
2
3
Description
MAXLOAD
MAXLOAD+3
MAXLOAD+2
MAXLOAD+1
Table 16-4. Packet Sizes That Clear RXRDY
Value
0
1
2
3
Description
MAXLOAD, MAXLOAD-1, MAXLOAD-2, MAXLOAD-3
MAXLOAD
MAXLOAD, MAXLOAD-1
MAXLOAD, MAXLOAD-1, MAXLOAD-2
To enable DMA operation for the endpoint receive channel, the DMAEN bit of the USBRXCSRHn
register should be set. To enable DMA operation for the endpoint transmit channel, the DMAEN bit
of the USBTXCSRHn register must be set.
See “Micro Direct Memory Access (μDMA)” on page 333 for more details about programming the
μDMA controller.
Initialization and Configuration
To use the USB Controller, the peripheral clock must be enabled via the RCGC2 register (see
page 258).
The initial configuration in all cases requires that the processor enable the USB controller and USB
controller’s physical layer interface (PHY) before setting any registers. The next step is to enable
the USB PLL so that the correct clocking is provided to the PHY.
The USB controller provides a method to set the current operating mode of the USB controller. This
register should be written with the desired default mode so that the controller can respond to external
USB events.
Endpoint Configuration
To start communication, the endpoint registers must first be configured. An endpoint must be
configured before enumerating to the Host controller.
The endpoint 0 configuration is limited because it is a fixed-function, fixed-FIFO-size endpoint. The
endpoint requires little setup but does require a software-based state machine to progress through
the setup, data, and status phases of a standard control transaction. The configuration of the
remaining endpoints is done once before enumerating and then only changed if an alternate
configuration is selected by the Host controller. Once the type of endpoint is configured, a FIFO
January 21, 2012
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