Comment by miratrix | Hacker News Reader

Comment by miratrix | Hacker News Reader

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The difference between DCH (the full-on high power state) and PCH (the lowest power, waiting-for-paging state) is about 2-orders of magnitude. Last time I measured, it was about ~100mA vs ~1mA (at ~3.7V) used by the radio. So, it's not couple of minutes of battery life, but rather _many_ hours of standby life instead. People usually aren't very happy when a fully charged phone dies overnight.

I've seen apps do some crazy things and it really has a significant effect in over-all battery life. A popular Android weather clock widget woke the phone up every minute to update the minute number on the graphics and updated the weather information every ~15 minutes (gps + radio!) which single handily crushed the standby battery life from multiple days to less than 8 hours.

Yes, I don't think _every_ decision should be based on minimizing the wake ups... but on the other hand, all developers should at least try to have as much understanding of the platforms that they're working on so that they know what trade-offs they're making with each feature they're adding.

I'm glad that Google has these videos available and that they're being picked up in places like HN.

Anecdata: I turn my phone's wifi off when not required because it has a significant effect on the battery life - particularly when I'm not in range of a wifi signal. I've had a full charge die on an 8-hour country drive because wifi was on. On the return trip, wifi was turned off and it behaved as expected.

Go for a long walk in the park? All that time your phone's wifi is straining to find a wifi signal. It's not as big a power sap as the screen, however it's constantly, silently in use and the screen isn't.

Wifi scanning is also pretty terrible for power consumption as you found out.

If you are on Android, my guess is that your phone was set to be connected to Wifi during sleep. You can control it by going to Wifi networks section -> menu -> Advanced -> Keep Wi-Fi on during sleep, then setting it to "Only when plugged in" or "Never".

If you're driving around with the phone set to leave the Wifi on during sleep, it'll be constantly going in and out of range of various Wifi connections. If the Wifi part is set for passive scan, then the processor needs to be kept up as the Wifi chip attempts to collect the BSSID of all the network it see and processor tries to figure out whether these networks have been seen or not. If it's set for active scan, then the Wifi needs to power up the radios to transmit beacons. Pretty bad news in either case, unfortunately.

I personally setup Llama to turn the wifi when I'm not connected to a tower that I previously defined as "wifi available". It's nifty because I never have to explicitly turn wifi off then back on during my travels. To add a new wifi zone, I simply add the cell tower to the previous list and let the app do the rest.

Llama by itself uses less battery than leaving the wifi chip on, even in passive scanning mode, as the phone is always looking and checking cell towers.

That's a clever idea! Couldn't Android track the "WiFi available" cells itself when you connect to a WiFi network?

That kind of frequent-on behavior is why the iPhone 5S has the new M7 chip.

What the hell? The M7 is a marketing label for some COTS silicon they licensed from some IP company somewhere (probably ARM/Broadcom or one of their associates).

It doesn't make unicorns shit rainbows or defy the laws of physics.

Your comment isn't only disrespectful, but also misses the point. It doesn't matter if the M7 is a custom design or bought off the shelf. As long as it needs less power than the application processor to sample the sensors at some frequency, it fulfills its purpose.

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