LM3S5739 Datasheet, PDF (677/856 Pages) Texas Instruments – Stellaris® LM3S5739 Microcontroller

Stellaris® LM3S5739 Microcontroller
17.3.2.5
USB Hubs
The following setup requirements apply to the USB Host controller only if it is used with a USB hub.
When a full- or low-speed Device is connected to the USB controller via a USB 2.0 hub, details of
the hub address and the hub port also must be recorded in the corresponding USB Receive Hub
Address Endpoint n (USBRXHUBADDRn) and USB Receive Hub Port Endpoint n
(USBRXHUBPORTn) or the USB Transmit Hub Address Endpoint n (USBTXHUBADDRn) and
USB Transmit Hub Port Endpoint n (USBTXHUBPORTn) registers. In addition, the speed at
which the Device operates (full or low) must be recorded in the USB Type Endpoint 0 (USBTYPE0)
(endpoint 0), USB Host Configure Transmit Type Endpoint n (USBTXTYPEn), or USB Host
Configure Receive Type Endpoint n (USBRXTYPEn) registers for each endpoint that is accessed
by the Device.
For hub communications, the settings in these registers record the current allocation of the endpoints
to the attached USB Devices. To maximize the number of Devices supported, the USB Host controller
allows this allocation to be changed dynamically by simply updating the address and speed
information recorded in these registers. Any changes in the allocation of endpoints to Device functions
must be made following the completion of any on-going transactions on the endpoints affected.
17.3.2.6
Babble
The USB Host controller does not start a transaction until the bus has been inactive for at least the
minimum inter-packet delay. The controller also does not start a transaction unless it can be finished
before the end of the frame. If the bus is still active at the end of a frame, then the USB Host controller
assumes that the target Device to which it is connected has malfunctioned, and the USB controller
suspends all transactions and generates a babble interrupt.
17.3.2.7
Host SUSPEND
If the SUSPEND bit in the USBPOWER register is set, the USB Host controller completes the current
transaction then stops the transaction scheduler and frame counter. No further transactions are
started and no SOF packets are generated.
To exit SUSPEND mode, set the RESUME bit and clear the SUSPEND bit. While the RESUME bit is
set, the USB Host controller generates RESUME signaling on the bus. After 20 ms, the RESUME bit
must be cleared, at which point the frame counter and transaction scheduler start. The Host supports
the detection of a remote wake-up.
17.3.2.8
USB RESET
If the RESET bit in the USBPOWER register is set, the USB Host controller generates USB RESET
signaling on the bus. The RESET bit must be set for at least 20 ms to ensure correct resetting of the
target Device. After the CPU has cleared the bit, the USB Host controller starts its frame counter
and transaction scheduler.
17.3.2.9
Connect/Disconnect
A session is started by setting the SESSION bit in the USB Device Control (USBDEVCTL) register,
enabling the USB controller to wait for a Device to be connected. When a Device is detected, a
connect interrupt is generated. The speed of the Device that has been connected can be determined
by reading the USBDEVCTL register where the FSDEV bit is set for a full-speed Device, and the
LSDEV bit is set for a low-speed Device. The USB controller must generate a RESET to the Device,
and then the USB Host controller can begin Device enumeration. If the Device is disconnected while
a session is in progress, a disconnect interrupt is generated.
November 17, 2011
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