86
Agere Systems Inc.
Data Sheet
May 2001
and Packet Payload Engine
Ambassador T8110 PCI-Based H.100/H.110 Switch
7 Clock Architecture
(continued)
7.7.1.3 H-Bus Clock Enable/Disable on Fallback
The previous Ambassador devices allowed a fallback mode (A/B fallback) which automatically allowed an H1x0
bus clock master to detect an error in its own output clock and remove itself from the bus, or a clock slave to detect
an error on its incoming clock and
promote
itself to clock master. The H-bus clocks include:
n
A clocks: CT_C8_A, /CT_FRAME_A
n
B clocks: CT_C8_B, /CT_FRAME_B
n
C clocks:
/C16±, /C4, C2, SCLK, /SCLKx2, /FR_COMP
Refer to Figure 24 and Table 65. The T8110 allows for this mode of operation in two ways:
Register 0x00109(7:4) = 0100: legacy mode, A/B fallback—when this mode is selected, the fallback triggers
allowed are predefined based on the main input clock selection, and the state machine which controls H-bus clock
enable/disable is activated.
Register 0x00109(7:4) = 1001: nonlegacy mode—when this mode is selected, the fallback trigger enable registers
determine what triggers a fallback, and the state machine which controls H-bus clock enable/disable is activated.
Figure 24. T8110 H-Bus Clock Enable States
The T8110
enters & leaves
these states
based on
Master Output
Enable clock
register
updates,
0x00220
Diag_ABC
= Drives A
Clocks, B Clocks and
C Clocks, no fallback
permitted
Initial
Diag_ABC
Diag_AB
C_Only
A_Only
A_Master
B_Only
B_Master
A_Error
B_Error
A Clocks Fail
B Clocks Fail
A Clocks Fail
B Clocks Fail
B Clocks Fail
A Clocks Fail
Reprogram
B Clocks
Reprogram
A Clocks
Diagnostic/Forced Clocking
Fallback Clocking, assumes
Fallback enabled in CKS register
Diag_AB
= Drives A
Clocks and B Clocks,
no fallback permitted
C_Only
= Drives C
Clocks only, no
fallback permitted
B_Only
= Drives B
Clocks, can be promoted
to master and drive C clocks
in fallbackcondition
A_Only
= Drives A
Clocks, can be promoted
to master and drive C clocks
in fallbackcondition
B_Master
= Drives B & C
Clocks, all clocks shut off
in fallbackcondition
A_Master
= Drives A & C
Clocks, all clocks shut off
in fallbackcondition
B_Error
= all clocks shut off,
waiting for B clocks to be
reprogrammed
A_Error
= all clocks shut off,
waiting for A clocks to be
reprogrammed