Toshiba TLCS-900/H1 Series Manual page 305

3. When generating toggle error of device controller
a. UDC operation
If USB host fails to receive ACK transmitted from the UDC in OUT transfer, the
USB host transmits the same data to the UDC again. When the FIFO is available
to receive, the UDC detects toggle error because of detecting the same data(having
the same toggle as the data which is received just before) and returns ACK. The
UDC rejects it because the data have already been received normally. Meanwhile,
if FIFO is not available, the UDC returns NAK and informs the USB host that it is
unable to receive.
b. USB1.1 Standard (from USB1.0 Standard description)
The priority of each process in USB1.0 and USB1.1 standard is explained as
follows in chapter "8.4.5.3 Function Response to an OUT Transaction". It shows
the priority of ACK response by toggle error (SequenceBitsMatch=No) is higher
than that of NAK response.
Table 3.10.4 Function Responses to OUT Transactions in Order of Precedence
Data Packet Receiver
Corrupted Halt
Feature
Yes N/A
No Set
No Not set
No Not set
No Not set
Since the UDC gives priority to detecting FIFO condition over toggle error, the
UDC returns NAK in the response to USB host when FIFO is not available
because it is full. This is shown in the flow chart "3.10.6(a-2) Receiving bulk mode".
Thus, the UDC operates differently from USB standard under conditions where
FIFO is not available.
For that reason, the UDC may generate the retry process several times in case
of toggle error, while USB standard finishes it after the first time.
That is, the UDC returns NAK if it receives the data including toggle error with
FIFO full. However, after FIFO becomes available, the UDC returns ACK to the
USB host and finishes the retry process.
4. When using the USB device controller in the TMP92CH21, a crystal oscillator is
recommended (USB standard ≤ 9 MHz±2500ppm). In this case, a maximum of 3
stages of external hub can be used due to the precision of this USB device controller
and the internal clock.
5. Limitation of using the Isochronous IN transfer
When using the Isochronous IN transfer, do not use other endpoints
Sequence Bits Function Can
Match Accept Data
N/A N/A
N/A N/A
No N/A
Yes Yes
Yes No
92CH21-303
TMP92CH21
Handshake
Returned
by Function
None
STALL
ACK
ACK
NAK
.
simultaneously
2009-06-19