CY28316
Programmable Output Frequency, Watchdog Timer,
and Recovery Output Frequency
Functional Description
The Programmable Output Frequency feature allows users to
generate any CPU output frequency in the range of 50 MHz to
248 MHz. Cypress offers the most dynamic and the simplest
programming interface for system developers to utilize this
feature in their platforms.
when the system hangs or gets unstable. System BIOS or
other control software can enable the Watchdog Timer before
it attempts to make a frequency change. If the system hangs
and a Watchdog Timer time-out occurs, a system reset will be
generated and a recovery frequency will be activated.
The Watchdog Timer and Recovery Output Frequency
features allow users to implement a recovery mechanism
Table 6. Register Summary
All the related registers are summarized in Table 6.
Name
Description
Pro_Freq_EN
Programmable output frequencies enabled.
0 = Disabled (default).
1 = Enabled.
When it is disabled, the operating output frequency will be determined by either the latched value of
FS[4:0] inputs or the programmed value of SEL[4:0]. If FS_Override bit is clear, latched FS[4:0] inputs
will be used. If the FS_Override bit is set, the programmed value of SEL[4:0] will be used. When it is
enabled, the CPU output frequency will be determined by the programmed value of CPUFSEL_N,
CPUFSEL_M, and the PLL Gear Constant. The program value of FS_Override, SEL[4:0] or the latched
value of FS[4:0] will determine the PLL Gear Constant and the frequency ratio between CPU and other
frequency outputs.
FS_Override
When Pro_Freq_EN is cleared or disabled,
0 = Select operating frequency by FS input pins (default).
1 = Select operating frequency by SEL bits in SMBus control bytes.
When Pro_Freq_EN is set or enabled,
0 = Frequency output ratio between CPU and other frequency groups and the PLL Gear Constant are
based on the latched value of FS input pins (default).
1 = Frequency output ratio between CPU and other frequency groups and the PLL Gear Constant are
based on the programmed value of SEL bits in SMBus control bytes.
CPU_FSEL_N,
CPU_FSEL_M
When Prog_Freq_EN is set or enabled, the values programmed in CPU_FSEL_N[7:0] and
CPU_FSEL_M[6:0] determine the CPU output frequency. The new frequency will start to load whenever
there is an update to either CPU_FSEL_N[7:0] or CPU_FSEL_M[6:0]. Therefore, it is recommended
to use word or block Write to update both registers within the same SMBus bus operation. The setting
of the FS_Override bit determines the frequency ratio for CPU and PCI. When FS_Override is cleared
or disabled, the frequency ratio follows the latched value of the FS input pins. When FS_Override is
set or enabled, the frequency ratio follows the programmed value of SEL bits in SMBus control bytes.
ROCV_FREQ_SEL
ROCV_FREQ_SEL determines the source of the recover frequency when a Watchdog Timer time-out
occurs. The clock generator will automatically switch to the recovery CPU frequency based on the
selection on ROCV_FREQ_SEL.
0 = From latched FS[4:0].
1 = From the settings of ROCV_FREQ_N[7:0] and ROCV_FREQ_M[6:0].
ROCV_FREQ_N[7:0], When ROCV_FREQ_SEL is set, the values programmed in ROCV_FREQ_N[7:0] and
ROCV_FREQ_M[6:0] ROCV_FREQ_M[6:0] will be used to determine the recovery CPU output frequency when a Watchdog
Timer time-out occurs. The setting of the FS_Override bit determines the frequency ratio for CPU and
SDRAM. When it is cleared, the same frequency ratio stated in the Latched FS[4:0] register will be
used. When it is set, the frequency ratio stated in the SEL[4:0] register will be used. The new frequency
will start to load whenever there is an update to either ROCV_FREQ_N[7:0] and ROCV_FREQ_M[6:0].
Therefore, it is recommended to use word or block Write to update both registers within the same
SMBus bus operation.
WD_EN
0 = Stop and reload Watchdog Timer. Unlock CY28316 from recovery frequency mode.
1 = Enable Watchdog Timer. It will start counting down after a frequency change occurs.
Note: CY28316 will generate system reset, reload a recovery frequency, and lock itself into a recovery
frequency mode after a Watchdog Timer time-out occurs. Under recovery frequency mode, CY28316
will not respond to any attempt to change output frequency via the SMBus control bytes. System
software can unlock CY28316 from its recovery frequency mode by clearing the WD_EN bit.
WD_TO_STATUS
Watchdog Timer Time-out Status bit.
0 = No time-out occurs (Read); Ignore (Write).
1 = Time-out occurred (Read); Clear WD_TO_STATUS (Write).
Rev 1.0,November 20, 2006
Page 11 of 17
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