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USB function
Receove SOF
Valid data in FIFO B
has been transferred?
Yes
Switch to FIFO A
Receive IN token
Valid data in FIFO A
has been transferred?
Yes
Send data to the host
Receive SOF
Valid data in FIFO A
has been transferred?
Yes
Switch to FIFO B
Receive IN token
Is there a valid data
in EP3i FIFO?
Yes
Send data to the host
Figure 15.20 EP3i Isochronous-In Transfer Operation
No
EP3i IN token not received
(Set EP3i TF of UIFR1 to 1)
FIFO A
Set EP3i transfer
No
request flag
(Set EP3i TR of UIFR1 to 1)
Send 0-byte data
EP3i IN token not received
No
(Set EP3i TF of UIFR1 to 1)
FIFO B
No
EP3i IN token not received
(Set EP3i TR of UIFR1 to 1)
Send 0-byte data
Firmware
Clear the SOF packet
detection flag
(Clear SOF of UIFR3 to 0)
Read USB time stamp
registers H and L
(UTSRH and UTSRL)
FIFO B
Write 1-packet data to the
USB endpoint data
register 3i (UEDR3i)
Start of Frame
Clear the SOF packet
detection flag
(Clear SOF of UIFR3 to 0)
Read USB time stamp
registers H and L
(UTSRH and UTSRL)
FIFO A
Write 1-packet data to the
USB endpoint data
register 3i
(UEDR3i)
Rev. 3.0, 10/02, page 505 of 686
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