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Strange time results for switching power management modes

Question asked by bergo on Feb 3, 2013
Latest reply on Dec 10, 2013 by Anson Huang

Hello,

I've complied the kernel from source code which downloaded from freescale's i.mx51 web site. compiled using ltib, striped the kernel down only to the essentials ( +included all the power management parts).

It seems to work fine,

but when I switch to STOP mode by using : echo mem > /sys/power/state

or WAIT mode by using :  echo standby > /sys/power/state

and then pressing the power button to return to RUN mode, I'm getting times which are much higher then expected

for RUN -> STOP -> RUN

"

root@freescale /home/user$ echo mem > /sys/power/state

PM: Syncing filesystems ... done.

Freezing user space processes ... (elapsed 0.01 seconds) done.

Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.

Suspending console(s) (use no_console_suspend to debug)

keup

PM: suspend of devices complete after 2.787 msecs

PM: late suspend of devices complete after 0.871 msecs

PM: early resume of devices complete after 0.890 msecs

<6>PWR key pressed

PM: resume of devices complete after 284.410 msecs

Restarting tasks ... done.

"

for RUN -> WAIT -> RUN

"

root@freescale /home/user$ echo standby > /sys/power/state

PM: Syncing filesystems ... done.

Freezing user space processes ... (elapsed 0.01 seconds) done.

Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.

Suspending console(s) (use no_console_suspend to debug)

keup

PM: suspend of devices complete after 2.760 msecs

PM: late suspend of devices complete after 0.872 msecs

PM: early resume of devices complete after 0.691 msecs

<6>PWR key pressed

PM: resume of devices complete after 185.325 msecs

Restarting tasks ... done.

"

 

According to "i.MX51 EVK Supply Current Measurements" page 17 ("Comparison between Power Consumption and Exit Time in Low Power Modes") the times should be around 115 micro second (and not mili second).

 

P.S

I found this while searching : [PATCHv2 1/2] ARM: mx51: Implement code to allow mx51 to enter WFI

 

The subject was different, but this guy got completely different results then I me when returning to RUN from STOP...

 

I was wondering what might have caused this huge time difference and how could I achieve a return to active time which is in the micro second and not mili second...

 

Many thanks in advance,

 



 


 

 

 

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