R01UH0823EJ0100 Rev.1.00
Page 952 of 1823
Jul 31, 2019
RX23W Group
32. USB 2.0 Host/Function Module (USBc)
(5) Isochronous Transfer Transmission Buffer Flush When the Function Controller is Selected
If an SOF packet of the next frame is received without receiving an IN token in an interval frame during isochronous data
transmission, the USB operates as if an IN token had been corrupted, and clears the buffer for which transmission is
enabled, putting that buffer in the writing enabled state.
If a double buffer configuration is used and writing to both buffers has been completed, the buffer memory that was
cleared is assumed as the data having been sent in the interval frame, and transmission is enabled for the buffer memory
that is not cleared with SOF packet reception.
The timing of the buffer flush function depends on the setting of the PIPEPERI.IITV[2:0] bits.
When the IITV[2:0] = 000b
The buffer flush operation starts from the next frame after the pipe becomes valid.
When the IITV[2:0] ≠ 000b
The buffer flush operation is carried out after the first successful transaction.
shows an example of the buffer flush function in the USB. When an unanticipated token is received before
the interval frame, the USB sends the write data or a zero-length packet as an underrun error according to the data setup
state.
Figure 32.19
Example of Buffer Flush Operation
SOF
Transfer enabled
Writing
Buffer A
Writing
ended
Writing
Writing ended
Empty
Empty
Empty Writing
Writing
ended
Transfer enabled
Buffer is flushed
Buffer B
SOF
SOF
SOF
