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USB Device Controller
Figure 6.
Isochronous OUT Transaction Phases and Interrupts
Successful data transfer from USB Host
ISO OUT Token
No handshake occurs. EP RX FIFO contains received data after data packet
completes. No interrupt occurs.
Reception of SOF causes SOF interrupt.
Note: An SOF interrupt is generated even if the SOF packet is corrupted.
SOF Token
SOF Interrupt
LH code for SOF interrupt service routine must fill all isochronous in EP TX FIFOs
with new transmit data and pull new receive data from all Isochronous Out EP RX
FIFOs.
Indicates a packet received by the device
Indicates a packet sent by the device
3.5.1
Isochronous OUT Endpoint Handshaking
3.5.2
Isochronous OUT Transaction Error Conditions
120
Universal Serial Bus (USB)
Figure 6 shows the two phases (ISO OUT token and data) of an isochronous
OUT data transfer in the top portion of the figure. No endpoint-specific interrupt
to the MPU is generated for the isochronous OUT transaction. The data for
isochronous endpoints are instead handled by the MPU at each start of frame
(SOF) interrupt, which is shown as the second case in Figure 6.
Data
Because isochronous endpoint transactions have no handshake packets, the
STAT_FLG.STALL,
STAT_FLG.NAK,
isochronous endpoints always return 0. Because there is no handshake, the
endpoint-specific interrupt for isochronous endpoints is not used.
If the MPU fails to read all of the data in the ISO OUT endpoint foreground FIFO
by the time the foreground and background FIFOs are switched (at the next
SOF), the endpoint FIFO that is being switched to the background is flushed,
and the STAT_FLG.DATA_FLUSH bit is asserted for the duration of the next
frame.
There is no special indication for the case in which the USB host does not
provide a transaction to an ISO OUT endpoint during a frame, but once the
and
STAT_FLG.ACK
bits
for
SPRU761A
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