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This section lists the valid CCN-502 power states and shows the power state transition diagram.
The following table shows the valid CCN-502 power states and their requirements.
Table 2-8 CCN-502 power states
|State||Description||Control logic||Snoop filter power state||L3 way[7:0] power state||L3 way[15:8] power state|
|FAM||Full run mode||On||On||On||On|
|HAM||Run mode with L3H1 (L3 upper ways) disabled.||On||On||On||Off|
|SF||Run mode with L3H1 and L3H2 disabled.||On||On||Off||Off|
|NOL3||Run mode with L3H1, L3H2, and SF disabled.||On||Off||Off||Off|
|FAM Dyn. Ret.||Run mode with L3H1, L3H2, and SF in retention.||On||Retention||Retention||Retention|
|HAM Dyn. Ret.||Run mode with L3H1 and SF in retention, and L3H2 in powerdown.||On||Retention||Retention||Off|
|SF Dyn. Ret.||Run mode with SF in retention, and L3H1 and L3H2 in powerdown.||On||Retention||Off||Off|
|FAM Static Ret.||Shutdown mode with L3H1, L3H2, and SF in retention.||Off||Retention||Retention||Retention|
|HAM Static Ret.||Shutdown mode with L3H1 and SF in retention, and L3H2 in powerdown.||Off||Retention||Retention||Off|
|SF Static Ret.||Shutdown mode with SF in retention, and L3H1 and L3H2 in powerdown.||Off||Retention||Off||Off|
The L3 cache operates in four main operational modes:
|FAM||Full-Associativity Mode, where the snoop filter and the entire L3 cache are used.|
|HAM||Half-Associativity Mode, where the snoop filter is enabled but the upper half of the L3 ways are disabled and powered off.|
|SFONLY||Snoop-Filter-Only mode, where the snoop filter is enabled but all the L3 cache is powered off.|
|NOL3||No-L3 mode, where the snoop filter and L3 cache are disabled and powered off.|
The following figure shows the valid power states and transitions for a CCN-502 system.
From FAM, HAM, or SFONLY, the L3 cache can enter a dynamic retention mode, where:
From these states, the L3 cache can also enter a static retention mode, where:
The difference between the dynamic and static retention modes is that dynamic retention is entered because of a dynamic activity or inactivity indicator from the HN-F to the SoC. This is an output of the HN-F that is used to determine periods of inactivity long enough to warrant entering retention mode, but not long enough or not the type of inactivity to make the SoC place the L3 and SF in static retention. In addition to the static retention modes, the control logic can be powered down from the NOL3 state, at which point the CCN-502 is fully off.
All activity that is required to enable safe transition between the respective power states is performed automatically by the HN-Fs in response to input P-Channel P-state transitions. No additional activity is required of the SoC logic to enable transitions between power states. For example, the HN-F performs clean and invalidation of half of the ways of the L3 and clean and invalidation of all ways of the L3, as required by the respective power state transitions.