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a) Back to Back Host Packets
During back to back host packets of the same transaction (e.g. token to data packet), a
minimum of 2 idle bit times are required from the end of the EOP's SE0 to the SOP of the
next packet. The bus is driven during this period,
b) Response Turnaround
After an IN data packet, the handshake packet is initiated within 1 bit time of the EOP
detection. The EOP detection delay is TBD. The only valid handshake from the host is an
ACK. If an error is detected, the host does not respond with any handshake.
c) Host Response Time-out
When waiting for a device to respond following a token or data packet, the transaction
times out after 16 bit times plus the delay of the SOP detection delay. The SOP detection
delay is TBD. A new transaction may begin after a total of 18 bit times. This is not expected
to be achievable due to latencies of the transaction's retirement and retrieval of the next
transaction.
d) Packet Error Time-out
When an incoming packet is rejected due to errors and the device expects a response, the
next transaction cannot begin until the previous transaction has timed-out at the device. The
minimum host delay from the end of the EOP's SE0 to the next SOP is a total of 18 bit
times.
4) Frame Timing (SOF, EOF)
The frame is controlled by the Frame Manager which issues SOF requests each frame period.
The SIE is further guaranteed to be idle when this request is generated by EOF timing marks
which allow any bus activity that threatens to interfere with SOF request to be terminated.
Table 18-16 summarizes the minimum USB EOF requirements and the value of
HcFmRemaining at which they occur.
Table 18.16 SIE EOF Timing Requirements
Parameter
HcFmRemaining
Description
EOF FS Start
47
Latest start time of a FS packet
EOF LS Start
184
Latest start time of a LS packet
EOF Rx Disable
41
Invalidate Rx packet beyond this time.
If software improperly sets the FSLargestDataPacket field of the HcFmInterval register or
HcLSThreshold, the transmitter may overrun the frame and miss the SOF event. As a hardware
fail-safe, the SIE terminates any packet such packet with a 16 bit time J state to generate a bit
stuff error and prevent a response.
Содержание HD64465
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