17.2.1.1.5 Device Mode Suspend
When no activity has occurred on the USB bus for 3 ms, the USB controller automatically enters SUSPEND
mode. If the SUSPEND interrupt has been enabled in the USB Interrupt Enable (USBIE) register, an interrupt
is generated at this time. When in SUSPEND mode, the PHY also goes into SUSPEND mode. When RESUME
signaling is detected, the USB controller exits SUSPEND mode and takes the PHY out of SUSPEND. If
the RESUME interrupt is enabled, an interrupt is generated. The USB controller can also be forced to exit
SUSPEND mode by setting the RESUME bit in the USB Power (USBPOWER) register. When this bit is set, the
USB controller exits SUSPEND mode and drives RESUME signaling onto the bus. The RESUME bit must be
cleared after 10 ms (a maximum of 15 ms) to end RESUME signaling. To meet USB power requirements, the
controller can be put into Deep Sleep mode which keeps the controller in a static state.
17.2.1.1.6 Start of Frame
When the USB controller is operating in device mode, it receives a Start-Of-Frame (SOF) packet from the Host
once every millisecond. When the SOF packet is received, the 11-bit frame number contained in the packet
is written into the USB Frame Value (USBFRAME) register, and an SOF interrupt is also signaled and can be
handled by the application. Once the USB controller has started to receive SOF packets, it expects one every
millisecond. If no SOF packet is received after 1.00358 ms, the packet is assumed to have been lost, and
the USBFRAME register is not updated. The USB controller continues and resynchronizes these pulses to the
received SOF packets when these packets are successfully received again.
17.2.1.1.7 USB Reset
When the USB controller is in device mode and a RESET condition is detected on the USB bus, the USB
controller automatically performs the following actions:
• Clears the USBFADDR register
• Clears the USB Endpoint Index (USBEPIDX) register
• Flushes all endpoint FIFOs
• Clears all control/status registers
• Enables all endpoint interrupts
• Generates a RESET interrupt
17.2.1.1.8 Connect/Disconnect
The USB controller connection to the USB bus is handled by software. The USB PHY can be switched between
normal mode and non-driving mode by setting or clearing the SOFTCONN bit of the USBPOWER register.
When the SOFTCONN bit is set, the PHY is placed in its normal mode, and the USB0DP/USB0DM lines of
the USB bus are enabled. At the same time, the USB controller is placed into a state, in which it does not
respond to any USB signaling except a USB RESET. When the SOFTCONN bit is cleared, the PHY is put
into non-driving mode, USB0DP and USB0DM are tristated, and the USB controller appears to other devices
on the USB bus as if it has been disconnected. The non-driving mode is the default so the USB controller
appears disconnected until the SOFTCONN bit has been set. The application software can then choose when
to set the PHY into its normal mode. Systems with a lengthy initialization procedure may use this to ensure that
initialization is complete, and the system is ready to perform enumeration before connecting to the USB bus.
Once the SOFTCONN bit has been set, the USB controller can be disconnected by clearing this bit.
Note:
The USB controller does not generate an interrupt when the device is connected to the Host. However, an
interrupt is generated when the Host terminates a session.
17.2.2 Operation as a Host
When the USB controller is operating in Host mode, it can either be used for point-to-point communications
with another USB device or, when attached to a hub, for communication with multiple devices. Full-speed and
low-speed USB devices are supported, both for point-to-point communication and for operation through a hub.
The USB controller automatically carries out the necessary transaction translation needed to allow a low-speed
or full-speed device to be used with a USB 2.0 hub. Control, bulk, and interrupt transactions are supported.
This section describes the USB controller's actions when it is being used as a USB Host. Configuration of IN
endpoints, OUT endpoints, entry into and exit from SUSPEND mode, and RESET are all described.
Universal Serial Bus (USB) Controller
1062
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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