user796345 February 2016

standby and sleep modes in a mobile phone

Consider the below case.

1) A mobile phone is booted. At this moment it can be said that it is in run mode where the power consumption is more. 2) If no activity is done, after sometime the screen goes dim. 3) After further inactivity, the screen completely goes off.

a) Now my question is, can we say that the mobile phone was in standby mode and sleep mode in above steps 2 and 3 respectively?

Another question is, suppose we are playing some music and we leave the mobile like that for sometime. In this case also the mobile phone goes through 2 and 3 steps mentioned above. But the only difference to earlier scenario is that music is being played in the second scenario. In this case, can we say that mobile phone was in standby and sleep mode respectively in 2 & 3 steps when the music is being played.

Answers


Saurabh Sengar February 2016

If no activity is there for Linux, CPUIDLE threads gets scheduled by scheduler as it is the least priority process and it brings the CPU to various low power states, where as other peripheral are governed by various other concepts of OS. If screen goes dim it can lead to two possibilities :

  1. Partial wake load is help and system is down (some power save)
  2. Linux suspend called (echo mem > /sys/power/stae) and full device is suspended, (huge power saves, as only ddr is active that to in self refreshing mode along with ALWAYS ON module) So just by seeing you cant say its in sleep or suspend mode, but if say your touch or some activity other then register WAKE UP event brings the screen up, your device was in sleep mode not suspend mode. WAKE UP events usually are "power on key", alarm, network packet (ie a call or message etc)

And for your second part of question, it belongs to low power audio concept, it varies alot with your device architecture. Most common in android phones are putting the cpu in 'Low power state' and periodically waking them up to copy the music data to DMA, which can be played.

There are so many concepts used in the scenario you have used varies with OS and architecture and application, I have tried my best to give you a bird's eye view.

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Asked in February 2016
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