AT%SLEEP=n power consumption

[Alastair Johnson]

Werner Almesberger wrote:
> I order to evaluate the impact of the AT%SLEEP=2 work-around, Joerg
> asked me to measure how the sleep mode affects the current drawn by
> the system.
> 
> Test setup:
> 
> - device is idle but (for convenience) not suspended
> - GSM is active and has registered with the network (AT+CFUN=1,
>   AT+COPS=0)
> - the test setup does not suffer from #1024
> - power is supplied to the battery terminals from a lab power supply
>   set to 4.0V
> - USB is not connected
> 
> Battery current of the whole system in mA. Values are from measurements
> averaged over about 15 minutes each:
> 
> at%sleep=       avg     min     max     samples
> 4                96.0    91.6   198.0   20006
> 3                98.4    91.6   214.6   21432
> 2               102.2    97.6   209.3   21428
> 1               104.0   101.9   197.2   21352
> 0               120.3   118.8   213.0   21452
> 
> Integration period is one power line cycle (20ms). There are transients
> much faster than 50Hz. E.g., sampling at 2.5kHz finds more noise but
> does not change the difference in the averaged value:
> 
> at%sleep=       avg     min     max     samples
> 4                95.1    63.1   242.5   210207
> 3                97.1    62.8   242.9   215460
> 2               101.4    68.7   243.4   208230
> 
> Note that this is an idle but not suspended system, hence the large
> minimum current.
> 
> So the difference between sleep=2 and sleep=4 is about 6mA. Joerg
> mentioned that the idle current of the GSM subsystem should be 4mA,
> so this would be an increase to 250%.
> 
> Andy, you once measured the power consumption when the overall system
> is perfectly suspended. Do you still remember how much it was ?
> 
> - Werner

Can you repeat the test on a handset that is suffering from #1024? I 
suspect that the frequent reregisters increase power consumption, but I 
don't have the equipment available to make the measurements. It 
certainly produces more instances of GSM interference on my PC speakers 
  which suggests more transmit operations. If this is the case then for 
those wth #1024 SLEEP=2 may be no worse, or possibly better, than SLEEP=4.