Atmel SAM9X25, Manual

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33.6.9.7 Isochronous IN
Isochronous-IN is used to transmit a stream of data whose timing is implied by the delivery rate.
Isochronous transfer provides periodic, continuous communication between host and device.
It guarantees bandwidth and low latencies appropriate for telephony, audio, video, etc.
If the endpoint is not available (TX_PK_RDY = 0), then the device does not answer to the host.
An ERR_FL_ISO interrupt is generated in the UDPHS_EPTSTAx register and once enabled,
then sent to the CPU.
The STALL_SNT command bit is not used for an ISO-IN endpoint.
33.6.9.8 High Bandwidth Isochronous Endpoint Handling: IN Example
For high bandwidth isochronous endpoints, the DMA can be programmed with the number of
transactions (BUFF_LENGTH field in UDPHS_DMACONTROLx) and the system should provide
the required number of packets per microframe, otherwise, the host will notice a sequencing
problem.
A response should be made to the first token IN recognized inside a microframe under the fol-
lowing conditions:
• If at least one bank has been validated, the correct DATAx corresponding to the programmed
Number Of Transactions per Microframe (NB_TRANS) should be answered. In case of a
subsequent missed or corrupted token IN inside the microframe, the USB 2.0 Core available
data bank(s) that should normally have been transmitted during that microframe shall be
flushed at its end. If this flush occurs, an error condition is flagged (ERR_FLUSH is set in
UDPHS_EPTSTAx).
• If no bank is validated yet, the default DATA0 ZLP is answered and underflow is flagged
(ERR_FL_ISO is set in UDPHS_EPTSTAx). Then, no data bank is flushed at microframe
end.
• If no data bank has been validated at the time when a response should be made for the
second transaction of NB_TRANS = 3 transactions microframe, a DATA1 ZLP is answered
and underflow is flagged (ERR_FL_ISO is set in UDPHS_EPTSTAx). If and only if remaining
untransmitted banks for that microframe are available at its end, they are flushed and an error
condition is flagged (ERR_FLUSH is set in UDPHS_EPTSTAx).
• If no data bank has been validated at the time when a response should be made for the last
programmed transaction of a microframe, a DATA0 ZLP is answered and underflow is flagged
(ERR_FL_ISO is set in UDPHS_EPTSTAx). If and only if the remaining untransmitted data
bank for that microframe is available at its end, it is flushed and an error condition is flagged
(ERR_FLUSH is set in UDPHS_EPTSTAx).
• If at the end of a microframe no valid token IN has been recognized, no data bank is flushed
and no error condition is reported.
At the end of a microframe in which at least one data bank has been transmitted, if less than
NB_TRANS banks have been validated for that microframe, an error condition is flagged
(ERR_TRANS is set in UDPHS_EPTSTAx).
Cases of Error (in UDPHS_EPTSTAx)
• ERR_FL_ISO: There was no data to transmit inside a microframe, so a ZLP is answered by
default.