Related Information
on page 3-1
For more information, refer to “Reset Sequencing” in the
Reset Manager
chapter in the
Cyclone V Device
Handbook, Volume 3
.
Safe Mode
Safe mode is enabled in the HPS by the assertion of a safe mode request from the reset manager or by a cold
reset. Assertion of the safe mode request from the reset manager sets the safe mode bit in the clock manager
control register. No other control register bits are affected by the safe mode request from the reset manager.
When safe mode is enabled, the main PLL hardware-managed clocks (C0-C2) are bypassed to the
osc1_clk
clock and are directly generated from the
osc1_clk
clock. While in safe mode, clock manager register
settings, which control clock behavior, are not changed. However, the hardware bypasses these settings and
uses safe, default settings.
The hardware-managed clocks are forced to their safe mode values such that the following conditions occur:
• The hardware-managed clocks are bypassed to the
osc1_clk
clock, including counters in the main
PLL.
• Programmable dividers select the reset default values.
• The flash controller clocks multiplexer selects the output from the peripheral PLL.
• All clocks are enabled.
A write by software is the only way to clear the safe mode bit (
safemode
) of the
ctrl
register.
Before coming out of safe mode, all registers and clocks need to be configured correctly. It is possible
to program the clock manager in such a way that only a cold reset can return the clocks to a functioning
Note:
state. Altera strongly recommends using Altera-provided libraries to configure and control HPS
clocks.
Interrupts
The clock manger provides one interrupt output, enabled using the interrupt enable register (
intren
).
The source of the interrupt is six inputs, namely, an achieving lock and a losing lock bit in the interrupt
status register (
inter
) for each PLL.
Clock Usage By Module
The following table lists every clock input generated by the clock manager to all modules in the HPS. System
clock names are global for the entire HPS and system clocks with the same name are phase-aligned at all
endpoints.
Clock Manager
Altera Corporation
cv_54002
Safe Mode
2-16
2013.12.30