Agere Systems Inc.
51
Data Sheet
May 2001
and Packet Payload Engine
Ambassador T8110 PCI-Based H.100/H.110 Switch
6 Operating Control and Status
(continued)
* The synchronized to frame command also has a diagnostic element
—instead of performing the command right at the frame boundary,
the user can elect to perform the command at a specified offset time from the frame boundary, by programming the Diag11 and Diag10
registers, 0x0014B—0x0014A.
6.1.7 Fallback Type Select Register
The upper nibble configures which H-bus clocks are selected to trigger a clock fallback event. Any of the
legacy
modes have predetermined trigger enables and ignore the fallback trigger register settings. Nonlegacy modes
require the fallback trigger register settings. For more details, see Section 7.7.1 on page 82.
The lower nibble configures the state machine that controls clock register set active/inactive assignments. There
are three possible selections. For more details, see Section 7.7 on page 82.
n
Disabled. No transitions of clock register X and Y sets to active/inactive.
n
Fixed secondary. Swap the active/inactive sets on a fallback event; swap them back when fallback is cleared.
n
Rotating secondary. Swap the active/inactive sets on a fallback event; maintain this state when fallback is
cleared.
6.1.8 Fallback Trigger Registers
The fallback trigger registers are used in conjunction with the fallback type select register and control which H-bus
clocks are enabled to trigger a clock fallback event in case of error. The sync reference inputs to DPLL1 and
DPLL2 can also trigger a clock fallback event upon detection of an error.
Table 28. Fallback Control Register
Byte
Address
Name
Bit(s) Mnemonic
Value
Function
0x00108
Fallback Control
7:0
FBCSR
0000 0000
0000 0001
0000 0010
0000 0100
0001 0001
0001 0010
0001 0100
0010 0000
NOP (default).
GO_CLOCKS command.
CLEAR_FALLBACK command.
FORCE_FALLBACK command.
GO_CLOCKS synchronized to frame*.
CLEAR_FALLBACK synchronized to frame*.
FORCE_FALLBACK synchronized to frame*.
COPY ACTIVE TO INACTIVE SET com-
mand.
Table 29. Fallback Type Select Register
Byte
Address
Name
Bit(s) Mnemonic
Value
Function
0x00109
Fallback Type
Select
7:4
FTRSN
0000
0001
0010
0100
1000
1001
NOP (default).
Legacy, fallback to OSC/4 on main select failure.
Legacy, fallback X/Y set on main select failure.
Legacy, fallback X/Y set on H-bus A/B failure.
Fallback trigger registers control fallback.
Fallback trigger registers control fallback and
H-Bus clock enable state machine is enabled.
Fallback is disabled (default).
Enable fixed secondary fallback.
Enable rotating secondary fallback.
3:0
FSMSN
0000
0001
0010