Waitcnt / Sleep? What is "turned off"?

bill190

Just curious, I read somewhere that while waitcnt is "waiting", this reduces power usage...

So the question is; What all is turned off in different situations?

One situation: Within an "additional cog running" when other cogs are still running, then this cog goes into waitcnt, I assume that no other functions for any other cogs would be turned off, only functions for that one cog?

How about the counters for that specific cog, would these be shutdown during a waitcnt? Or left running?

Then there would be the situation where only cog 0 was running, if this was the case, would the entire chip be shutdown (or more things shut down) in that situation?

If yes, what all would be shut down?


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Mike Green

There are 9 major subunits in the Propeller, the 8 cogs and the hub. The hub is always powered. Other than the memories (RAM and ROM), the power consumption of the hub is small and relatively constant. The power consumption of the memories depends on how much they're accessed which depends partly on how many cogs are active.

Cogs draw minimal current when they're stopped (their initial state). When they're active (started by some other cog or by the reset circuitry), they draw current. When a WAITCNT / WAITPNE / WAITPEQ / WAITVID is "stalled", the cog drops into a low power state much like when they're stopped. Most of the logic is shut down. The counters (if active) continue to run. The video generator (if active) continues to run although will run out of data if not resupplied relatively quickly. Remember that the Propeller's clock is static. There is no minimum clock speed. Gates and registers will maintain their contents although their power consumption will drop drastically.

The graphs in the Propeller Datasheet give typical power consumption for various clock speeds, supply voltages, and types of activities for a cog and for the hub.