
IDT Upstream Port Failover
PES34H16 User Manual
2 - 4
October 30, 2008
Notes
When a dynamic upstream port failover is initiated, the PES34H16 takes the following actions:
–
The LTSSM associated with the upstream port immediately transitions to the Detect state and the
data link layer transitions to the DL_Down state. This causes data in the replay buffer associated
with the upstream port and upstream port data queued in the switch core to be discarded.
–
The state of the SerDes multiplexors are modified to select the new upstream port.
–
The LTSSM initiates link training with the upstream port.
The following sections describe the manner in which a dynamic upstream port failover may be initiated.
In most systems it is expected that only one upstream failover mechanism will be enabled at a time. If a
failover of the same type (i.e., software, signal, or watchdog timer) is initiated while one is already in prog-
ress, then the second initiation will be lost. If a failover of a different type is initiated while one is in progress,
then the second failover will be performed when the one in progress is completed. Software may utilize the
Upstream Failover Change (USPC) and Upstream Failover Change Initiated (USPCI) bits in the Upstream
Port Failover Status (USPFSTS) register to avoid failover race conditions.
Software Initiated Failover
An upstream port failover may be initiated by modifying the state of the Upstream Port Software Select
(USPSEL) field in the Upstream Port Failover Control (USPFCTL) register when the switch is selected to
operate in an upstream failover mode. A software initiated failover may be instituted by software running on
the root or software running on the device that writes to the USPSEL field via the SMBus. The USPSEL
field should not be modified during an upstream port failover (i.e., failover requests are not queued).
Signal Initiated Failover
An upstream port failover may be initiated by a change in the state of the Upstream Port Select
(USPSEL) signal. Such a failover is initiated when:
1. the Upstream Port Signal Failover Enable (SIGFEN) bit is set in the Upstream Port Failover Control
(USPFCTL) register
2. the switch is selected to operate in an upstream failover mode, and
3. the upstream port selected by the USPSEL signal differs from the current upstream port.
The USPSEL signal is an alternate function of GPIO[4]. The state of the USPSEL signal always reflects
the state of the GPIO[4] pin regardless of whether or not GPIO[4] is configured to operate as an alternate
function. When USPSEL is negated (low), port 0 is selected as the upstream port. When USPSEL is
asserted (high), port 2 is selected as the upstream port. The state of the USPSEL signal should not be
modified more frequently than once per second. The behavior of the PES34H16 is undefined when the
USPSEL signal is modified more frequently than this rate.
Watchdog Timer Initiated Failover
An upstream port failover may be initiated as the result of an expiration of a watchdog timer. Such a
failover is initiated when:
1. the Upstream Port Timer Failover Enable (TIMFEN) bit is set in the Upstream Port Failover Control
(USPFCTL) register
2. the switch is selected to operate in an upstream failover mode, and
3. the Watchdog Timer Count (COUNT) field in the Upstream Port Failover Watchdog Timer
(USPFTIMER) transitions from a one to a zero.
When non-zero, the COUNT field in the USPFTIMER is decremented once per microsecond (1 µ S).
This provides a maximum watchdog timer interval of over one hour. Decrementing of the COUNT field
ceases when zero is reached. The COUNT field may be written by software at any time. Modifying the
count field is used to rearm the watchdog timer. If not expired, the watchdog timer continues to decrement
across a hot-reset.
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Страница 18: ...IDT Register List PES34H16 User Manual xii October 30 2008 Notes...
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Страница 86: ...IDT Power Management PES34H16 User Manual 7 4 October 30 2008 Notes...
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