Datasheet

8−6
SLLS535E − April 2008TUSB6250
− The firmware then performs a read to the USBWKUP register to reveal which status-change event bit
is set. If multiple events occurred, the firmware must service all of them individually.
− After servicing the WAKCLK interrupt for each individual status-change event, the firmware must write
a 1 to the corresponding bit in the USBWKUP register to clear such status-change event.
8.3.2.2 WAKCLK Interrupt Function During Normal Operation (When the TUSB6250 is not in
the USB Suspend State)
The WAKCLK interrupt provided by the TUSB6250 can be used for a variety of functions under different
operating conditions, other than just the remote wakeup interrupt in the suspend state. These functions can
include compact flash card detection, removable media insertion/eject, or an external event from another
on-board DSP as an end-product-specific-function, etc.
In other words, other than the VBUS status-change detection that has its fixed functionality, the other three
status-change events can be implemented as interrupt-specific to an end-product function as described
previously.
8.3.2.3 WAKCLK Interrupt Functions as a Remote Wakeup Interrupt (When the TUSB6250 is
in the USB Suspend State)
One common function of the WAKCLK interrupt is that it can be used as the remote wakeup interrupt. If the
TUSB6250 is in the USB suspend state, as long as the remote wakeup and the individual WAKCLK
status-change event detection (no need for VBUS detection, which is always enabled) are enabled, any VBUS
or status-change event causes the TUSB6250 to wake the core clock up, generate a WAKCLK interrupt to
the MCU, and send USB resume signaling to the upstream USB host. The resume signaling is sent by the
TUSB6250 hardware when either the WAKCLK interrupt is cleared by the firmware or 10 ms is reached after
the hardware triggers the WAKCLK interrupt to the MCU, whichever occurs first.
It is important to understand that all USB devices only report to the upstream USB host whether they are
remote wakeup capable. It is up to the USB host to decide whether to enable a USB device’s remote wakeup
capability through the Set_Feature command.
The TUSB6250 offers a unique feature that allows its remote wakeup capability to be disabled, while the
TUSB6250 is still able to capture and remember the status-change event that occurred during the USB
suspend state.
When the TUSB6250 is in the suspend state, with the remote wakeup disabled (RWUPEN bit of the USBCTL
register is cleared), the following two scenarios describe whether and how the core clock of the TUSB6250
is awakened due to the WAKCLK status-change event.
• If the low-power enable bit (LPEN) is not set in the USBCTL register, the TUSB6250 has no need to wake
the clock up, because the clock is not disabled and is still running during suspend. Any valid WAKCLK
status-change event can cause a WAKCLK interrupt to be generated. This normally happens for a
self-powered application.
• If the low-power enable bit (LPEN) is set in the USBCTL register, the core clock is shut down during
suspend. The WAKCLK interrupt event that occurred during suspend is captured and remembered using
asynchronous logic, however no interrupt is triggered. The TUSB6250 keeps the core clock shut down
and remains in the suspended state until the core clock is available, which is when the USB host signals
resume to the TUSB6250. When the core clock is available, the remembered WAKCLK event triggers the
actual interrupt.