Usb Reset Signaling - Motorola DragonBall MC9328MX1 Reference Manual

USB Device Port

28.9.4 USB Reset Signaling

Reset signaling can occur on the USB for a number of reasons. When the device receives reset signaling, it
means that the host is preparing to re-enumerate the bus. All transactions in progress must be invalidated,
and the device software prepared to receive configuration changes.
Because the device can contain valid, but as-yet unread, data in the FIFOs when USB reset signaling
occurs, the hardware does not flush the FIFOs. When device software receives reset signaling, it completes
reading any unread data from the FIFOs and execute FIFO flush operations on all of the FIFOs. This
guarantees that the datapath is empty and ready for new data transfer operations when reset signaling and
re-enumeration are complete.
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