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Section 26 USB 2.0 Host/Function Module
Page 1540 of 2108 R01UH0134EJ0400 Rev. 4.00
Sep 24, 2014
SH7262 Group, SH7264 Group
(4) Setup of Data to be Transmitted using Isochronous Transfer when the Function
Controller Function is Selected
With isochronous data transmission using this module in function controller function, after data
has been written to the buffer memory, a data packet can be sent with the next frame in which an
SOF packet is detected. This function is called the isochronous transfer transmission data setup
function, and it makes it possible to designate the frame from which transmission began.
If a double buffer is used for the buffer memory, transmission will be enabled for only one of the
two buffers even after the writing of data to both buffers has been completed, that buffer memory
being the one to which the data writing was completed first. For this reason, even if multiple IN
tokens are received, the only buffer memory that can be sent is one packet's worth of data.
When an IN token is received, if the buffer memory is in the transmission enabled state, this
module transmits the data. If the buffer memory is not in the transmission enabled state, however,
a zero-length packet is sent and an underrun error occurs.
Figure 26.20 shows an example of transmission using the isochronous transfer transmission data
setup function with this module, when IITV = 0 (every frame) has been set.