TM4C123FH6PM Datasheet, PDF (1074/1371 Pages) Texas Instruments – Tiva™ TM4C123FH6PM Microcontroller

Universal Serial Bus (USB) Controller
17.4.2
When the USB controller is acting as a Host, it is in control of two signals that are attached to an
external voltage supply that provides power to VBUS. The Host controller uses the USB0EPEN signal
to enable or disable power to the USB0VBUS pin on the USB connector. An input pin, USB0PFLT,
provides feedback when there has been a power fault on VBUS. The USB0PFLT signal can be
configured to either automatically negate the USB0EPEN signal to disable power, and/or it can
generate an interrupt to the interrupt controller to allow software to handle the power fault condition.
The polarity and actions related to both USB0EPEN and USB0PFLT are fully configurable in the USB
controller. The controller also provides interrupts on Device insertion and removal to allow the Host
controller code to respond to these external events.
Endpoint Configuration
To start communication in Host or Device mode, the endpoint registers must first be configured. In
Host mode, this configuration establishes a connection between an endpoint register and an endpoint
on a Device. In Device mode, an endpoint must be configured before enumerating to the Host
controller.
In both cases, the endpoint 0 configuration is limited because it is a fixed-function, fixed-FIFO-size
endpoint. In Device and Host modes, 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. In Device mode, 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. In Host mode, the endpoints must be configured to operate as control, bulk, interrupt or
isochronous mode. Once the type of endpoint is configured, a FIFO area must be assigned to each
endpoint. In the case of bulk, control and interrupt endpoints, each has a maximum of 64 bytes per
transaction. Isochronous endpoints can have packets with up to 1023 bytes per packet. In either
mode, the maximum packet size for the given endpoint must be set prior to sending or receiving
data.
Configuring each endpoint's FIFO involves reserving a portion of the overall USB FIFO RAM to
each endpoint. The total FIFO RAM available is 2 Kbytes with the first 64 bytes reserved for endpoint
0. The endpoint's FIFO must be at least as large as the maximum packet size. The FIFO can also
be configured as a double-buffered FIFO so that interrupts occur at the end of each packet and
allow filling the other half of the FIFO.
If operating as a Device, the USB Device controller's soft connect must be enabled when the Device
is ready to start communications, indicating to the Host controller that the Device is ready to start
the enumeration process. If operating as a Host controller, the Device soft connect must be disabled
and power must be provided to VBUS via the USB0EPEN signal.
17.5
Register Map
Table 17-5 on page 1074 lists the registers. All addresses given are relative to the USB base address
of 0x4005.0000. Note that the USB controller clock must be enabled before the registers can be
programmed (see page 343). There must be a delay of 3 system clocks after the USB module clock
is enabled before any USB module registers are accessed.
Table 17-5. Universal Serial Bus (USB) Controller Register Map
Offset Name
Type
Reset
Description
0x000
0x001
USBFADDR
USBPOWER
RW
0x00
USB Device Functional Address
RW
0x20
USB Power
See
page
1082
1083
1074
Texas Instruments-Production Data
June 12, 2014