AT90USB1286_14 Datasheet, PDF (271/456 Pages) ATMEL Corporation – Optional Boot Code section with independent lock bits

AT90USB64/128
23.14.2.1 Abort
If the endpoint uses two banks, the second one can be read by the HOST while the current is
being written by the CPU. Then, when the CPU clears FIFOCON, the next bank may be already
ready (free) and TXINI is set immediately.
An “abort” stage can be produced by the host in some situations:
• In a control transaction: ZLP data OUT received during a IN stage
• In an isochronous IN transaction: ZLP data OUT received on the OUT endpoint during a IN
stage on the IN endpoint
• ...
The KILLBK bit is used to kill the last “written” bank. The best way to manage this abort is to per-
form the following operations:
Table 23-1. Abort flow.
Endpoint
Abort
Clear
UEIENX.
TXINE
NBUSYBK
=0
Yes
Endpoint
reset
No
KILLBK=1
Yes _KILLBK=1
No
Disable the TXINI interrupt.
Abort is based on the fact
that no banks are busy,
meaning that nothing has to
be sent.
Kill the last written
bank.
Wait for the end of the
procedure.
Abort done
23.15 Isochronous mode
23.15.1 Underflow
An underflow can occur during IN stage if the host attempts to read a bank which is empty. In
this situation, the UNDERFI interrupt is triggered.
An underflow can also occur during OUT stage if the host send a packet while the banks are
already full. Typically, he CPU is not fast enough. The packet is lost.
It is not possible to have underflow error during OUT stage, in the CPU side, since the CPU
should read only if the bank is ready to give data (RXOUTI=1 or RWAL=1)
23.15.2 CRC error
A CRC error can occur during OUT stage if the USB controller detects a bad received packet. In
this situation, the STALLEDI interrupt is triggered. This does not prevent the RXOUTI interrupt
from being triggered.
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