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4.2.4. Altering Warm Reset System Response
Registers in the clock manager, system manager, and reset manager control how warm reset affects the HPS. You can control the impact of a warm reset on the clocks and I/O elements.
Intel strongly recommends using provided libraries to configure and control this functionality.
The default warm reset behavior takes all clocks and I/O elements through a cold reset response. As your software becomes more stable or for debug purposes, you can alter the system response to a warm reset. The following suggestions provide ways to alter the system response to a warm reset. None of the register bits that control these items are affected by warm reset.
- Boot from on‑chip RAM—enables warm boot from on‑chip RAM instead of the boot ROM. When enabled, the boot ROM code validates the RAM code and jumps to it, making no changes to clocks or any other system settings prior to executing user code from on‑chip RAM.
- Disable safe mode on warm reset—allows software to transition through a warm reset without affecting the clocks. Because the boot ROM code indirectly configures the clock settings after warm reset, Intel recommends that safe mode should only be disabled when the HPS is not booting from a flash device.
- Disable safe mode on warm reset for the debug clocks—keeps the debug clocks from being affected by the assertion of safe mode request on a warm reset. This technique allows fast debug clocks, such as trace, to continue running through a warm reset. When enabled, the clock manager configures the debug clocks to their safe frequencies to respond to a safe mode request from the reset manager on a warm reset. Disable safe mode on warm reset for the debug clocks only when you are running the debug clocks off the main PLL VCO and you are certain the main PLL cannot be impacted by the event which caused the warm reset.
- Use the osc1_clk clock for debug control—keeps the debug base clock (main PLL C2 output) always bypassed to the osc1_clk external clock, independent of other clock manager settings. When implemented, disabling safe mode on warm reset for the debug clocks has no effect.