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USB Device Port
28.7.6.2 The SYNCH_FRAME Standard Request
The SYNCH_FRAME standard request allows synchronization between the USB host and device during
isochronous operations. The command is passed through endpoint 0 as a device request and must be
processed by the device driver software.
28.8 Interrupt Services
The USB module generates a number of interrupts to indicate situations requiring attention from the host.
The types of interrupts are broken into two categories: USB general interrupts and Endpoint specific
interrupts. These interrupts are discussed in this section, as well as missed interrupts and their behaviors.
28.8.1 USB General Interrupts
The USB general interrupts indicate such things as global configuration and status changes pertaining to
the USB. All of these interrupts are maskable. When an event causes an interrupt condition to occur, and
the corresponding bit in the interrupt mask register is zero, an interrupt signal asserts on the module's
interface. Writing 1 to the associated bit in the interrupt register clears the interrupt. After a hard reset, all
interrupts are masked by default. This section describes each of the USB General Interrupts.
28.8.1.1 MSOF—Missed Start-of-Frame
The MSOF interrupt is used to inform software that it did not service the SOF interrupt before another SOF
interrupt was received.
28.8.1.2 SOF—Start-of-Frame
The SOF interrupt means that a start-of-frame token was received by the device. The current USB frame
number can be read from the USB_FRAME register. The start-of-frame interrupt is usually used by
isochronous devices to provide a stable timebase.
28.8.1.3 RESET_STOP—End of USB Reset Signaling
The RESET_STOP interrupt means that reset signaling on the USB has stopped.
28.8.1.4 RESET_START—Start of USB Reset Signaling
The RESET_START interrupt indicates that reset signaling on the USB has begun. When reset signaling is
active on the USB, the device does not expect to receive any transactions on the bus. This interrupt results
in a reset of the UDC into the powered state, however it does not cause any specific actions in the USB
Core front-end logic. User software must clear any pending interrupts and ensure that the module is
configured properly after the reset. This interrupt indicates the start of reset signaling. Status of the USB at
any given moment can be verified by examining the USB_STAT register.
Presence of USB reset signaling invalidates any transaction in progress. On detection of RESET_START,
user software reads any remaining valid data from the receive FIFOs and flushes all others. When reset
signaling is detected, user software must clear any pending interrupts and ensure that the module is
configured properly after the reset.
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MC9328MX1 Reference Manual
MOTOROLA
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