IDT NTB Upstream Port Failover
PES16NT2 User Manual
7 - 4
April 15, 2008
Notes
The following sections describe the manner in which a dynamic upstream port failover may be initiated.
Software Initiated Failover
A failover may be initiated by modifying the state of the NTB Upstream Port Failover Mode Select
(FOVRMSEL) field in the Failover Control (FOVRCTL) register. A software initiated failover may be insti-
tuted by software running on the primary or secondary root, software running on a device that writes to the
USPSEL field via the SMBus, or via serial EEPROM initialization. The FOVRMSEL field should not be
modified during an NTB 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 NTB Upstream Port Failover
(FAILOVERP) signal. Such a failover is initiated when the Signal Failover Enable (SIGFEN) bit is set in the
Failover Control (FOVRCTL) register and the state of the FAILOVERP signal differs from the current
failover mode reported in the CFMODE field of the FOVRSTS register.
The FAILOVERP signal is an alternate function of GPIO[5]. The state of the FAILOVERP signal always
reflects the state of the GPIO[5] pin regardless of whether or not GPIO[5] is configured to operate as an
alternate function. When FAILOVERP is negated (low), normal mode is selected. When FAILOVERP is
asserted (high), failover mode is selected. The state of the FAILOVERP signal should not be modified more
frequently than once per second. The behavior of the PES16NT2 is undefined when the FAILOVERP signal
is modified more frequently than this rate.
Watchdog Timer Initiated Failover
An NTB upstream port failover may be initiated as the result of an expiration of a watchdog timer. Such
a failover is initiated when the Timer Failover Enable (TIMFEN) bit is set in the Failover Control (FOVRCTL)
register, and the Watchdog Timer Count (COUNT) field in the Failover Watchdog Timer (FOVRTIMER) tran-
sitions from a one to a zero.
When non-zero, the COUNT field in the USPFTIMER is decremented once per microsecond (1 µS).
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.
When a watchdog timer failover is initiated, the failover mode selected is the one not reported in the
CFMODE field in the FOVERSTS register. For example, if the current mode is normal mode, then the mode
following a watchdog timer initiated failover is failover mode.
System State Preservation
The PES16NT2 contains mechanisms that allow system state of the internal and/or external PCIe hier-
archy domains to be preserved across a dynamic failover. They may also be used to inhibit the propagation
of reset due to a link down or reception of TS1 ordered-sets indicating a hot reset.
– When the Internal Hierarchy Disable Link Down Hot Reset (IDLDHRST) bit is set in the FOVRCTL
register, the resetting of the internal and external NTB domains is inhibited due to a Port A link
down condition (i.e., a transition to DL_Down).
– When the External Hierarchy Disable Link Down Hot Reset (EDLDHRST) bit is set in the
FOVRCTL register, the resetting of the external NTB domain is inhibited due to a Port C link down
condition.
– When the Disable Failover Hot Reset (DFHRST) bit is set in the FOVRCTL register, the resetting
of the internal and external NTB domains is inhibited due to Port A and C link down conditions
resulting from a dynamic failover. Port A and C link down resulting from any other condition
continues to generate a hot reset unless masked by the IDLDHRST or EDLDHRST bits.
– When the Internal Hierarchy Disable Hot Reset Propagation (IDHRSTPROP) bit is set in the
FOVRCTL register, reception of TS1 ordered-sets on the upstream port indicating a hot reset is
ignored.
– When the External Hierarchy Disable Hot Reset Propagation (EDHRSTPROP) bit is set in the
FOVRCTL register, reception of TS1 ordered-sets on port C indicating a hot reset is ignored.
Содержание 89HPES16NT2
Страница 14: ...DT List of Figures PES16NT2 User Manual viii April 15 2008 Notes...
Страница 20: ...IDT Register List PES16NT2 User Manual xiv April 15 2008 Notes...
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