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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Time Synchronization
Hardware Assist (TSYNC)
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
836
Order Number: 306262-004US
19.4
Theory of Operation (Auxiliary Snapshots)
19.4.1
Master Mode Programming Considerations
In master mode, the host processor firmware has complete control over both the
incoming auxiliary snapshot signal and the clearing of the snapshot lock. Firmware will
assert the signal, wait for the snapshot lock to set, read the snapshot, negate the
signal, and then clear the lock. Since it has control over the environment, firmware will
not clear the lock before it negates the signal. If the firmware does not clear the
incoming auxiliary snapshot signal before the TSYNC lock is cleared, then a second /
redundant snapshot event will be generated.
19.4.2
Slave Mode Programming Considerations
In slave mode, the host processor firmware typically knows the parameters of the
signal coming from the master. The pulse per second signal from the GPS, for example,
has a documented width, and the firmware must be designed to wait that amount of
time after it detects the snapshot lock to the time it clears the lock. The firmware "wait"
is facilitated by the fact that GPIO[8:7] should be configured as inputs to read this
signal and assure that it is de-asserted before clearing the lock. Furthermore, the GPIO
input can be configured to interrupt the CPU on the falling edge of the auxiliary
snapshot signal, again making it easy for the firmware to know when to clear the lock.
Hardware filtering and edge-detection were considered but not implemented because
the signal quality from the master could be bad enough to cause spurious locks. For
example, cables to a GPS could be a kilometer or more in length and the type of cable
could be a factor as well.
Note:
The host processor firmware handles the filtering and MUST not clear the lock until
after the master has negated the snapshot input.
19.5
Detailed Register Descriptions
19.5.1
Register Map
The registers of the TSync registers reside within the memory map of the IXP45X/
IXP46X network processors.
presents the address offset for the TSync
registers, the names and mnemonics of the registers, and their access capability.
Subsequent sections describe the contents of these registers in greater detail. The
mnemonic names match names used in RTL code.
Table 267.
Register Legend
Attribute
Legend
Attribute
Legend
RV
Reserved
RC
Read Clear
PR
Preserved
RO
Read Only
RS
Read/Set
WO
Write Only
RW
Read/Write
NA
Not Accessible
RW1C
Normal Read
Write ‘1’ to clear
RW1S
Normal Read
Write ‘1’ to set