OMAP Wireless COnnectivity NLCP Suspend Resume Operation

Suspend/Resume

Modes of Operation

Two mode of operation are supported by NLCP:

• Suspend state:

The wl1xxx chip will be held in shutdown mode, were the host disable the WLAN portion by keeping the WLAN_Enable signal OFF, in that mode the wl1xxx consumes minimal current consumption.

• WOWLAN state:

The host is shutting down but the WLAN chip is being kept active (WLAN enable pin remains active). This allows the wl12xx firmware to remain active during suspend and if the system is configured to allow the WLAN interrupt to wakeup the host, it can trigger a system resume when a specific packet is recived by the wl12xx firmware.

How to operate Suspend Resume

to enable the omap to enter sleep, low voltage, & low power perform the following:

mount -t debugfs debugfs /tmp

To enter suspend mode:

echo mem > /sys/power/state

To Resume from suspend:

Serial console activity or other configured wakeup sources (keypad, touchscreen) will trigger resume

Suspend Resume Example - Shutdown mode

• connect to AP with WPA supplicant
• get IP address from the AP
• send ping to the AP
• Enter Suspend mode

root@am335x-evm:~# echo mem > /sys/power/state

Following is the screen shot shows how the Host is entering suspend mode, also the wl1271 is suspended

root@am335x-evm:~# echo mem > /sys/power/state
[ 2700.250152] PM: Syncing filesystems ... done.
[ 2700.438964] Freezing user space processes ... (elapsed 0.01 seconds) done.
[ 2700.459655] Freezing remaining freezable tasks ... (elapsed 0.01 seconds) don
e.
[ 2700.479644] Suspending console(s) (use no_console_suspend to debug)
[ 2700.487701] wl12xx: down

• in order to resume from suspend, hit any key on the terminal, or touch the EVM screen

[ 2700.626983] PM: suspend of devices complete after 139.770 msecs
[ 2700.628662] PM: late suspend of devices complete after 1.586 msecs
[ 2702.417083] GFX domain entered low power state
[ 2702.626098] PM: early resume of devices complete after 208.526 msecs
[ 2702.919403]
[ 2702.919403] CPSW phy found : id is : 0x4dd074
[ 2702.920989] PHY 0:01 not found
[ 2702.924438] wl12xx: state: 0
[ 2703.337097] wl12xx: PHY firmware version: Rev 8.4.999.A2.129
[ 2703.376922] wl12xx: firmware booted (Rev 8.2.0.0.100)
[ 2703.404998] PM: resume of devices complete after 778.269 msecs
[ 2703.462646] Successfully transitioned all domains to low power state
[ 2703.469451] Restarting tasks ... done.
root@am335x-evm:~# [ 2705.917572] PHY: 0:00 - Link is Up - 100/Full
[ 9905.223297] wlan0: deauthenticated from e0:91:f5:ea:9e:ee (Reason: 7) 
[ 9905.360504] cfg80211: Calling CRDA to update world regulatory domain
[ 9905.997711] wlan0: authenticate with e0:91:f5:ea:9e:ee (try 1)
[ 9906.007141] wlan0: authenticated
[ 9906.060241] wlan0: associate with e0:91:f5:ea:9e:ee (try 1)
[ 9906.069732] wlan0: RX ReassocResp from e0:91:f5:ea:9e:ee (capab=0x411 status=0 aid=1)
[ 9906.078033] wlan0: associated
[ 9906.185882] wl1271: Association completed.

• at that point the Station had reconnectd to the AP, and Ping should resume

Suspend/Resume - WOWLAN Wake on WLAN) mode

Comment: With current AM335x EVM, the Suspend resume in WOWLAN mode will not work due to HW limitations, wiki page with the needed rework will be ready soon, following description assumes a board that does not have the HW limitation.
The HW limitation is using the proper IRQ line that can wake up the Host from suspend, and use proper GPIO for the WLAN Enable signal that does not loose its context while suspend mode.

Before we enter suspend mode we need to declare which event triggers the wake up. In this example we will set the trigger to any which means any event (console activity, magic frame, etc) will wake up the board:

iw phy0 wowlan enable any

To enter suspend mode type:

echo mem > /sys/power/state

To Resume from suspend:
There are 2 option to resume from Suspend

1. Serial console activity or other configured wakeup sources (keypad, touchscreen) will trigger resume
2. Send Magic frame from other Station to the Station that is in suspend mode

Suspend Resume Example - Wowlan mode

In this setup we have:

• Two EVM's which are controlled via PC's with serial ports
• One AP

the Procedure will be as followes:

• Connect both stations (EVM) to the AP.
• Enter the first EVM to suspend in WOWLAN mode.
• Send ping to the first EVM from the Second EVM.
• That ping will cause the first EVM to wake from suspend.

Enter the first EVM to Suspend mode, by calling the following command:

root@am37x-evm:/usr/bin# echo mem > /sys/power/state

Following is the screen shot shows how the Host is entering suspend mode, also the wl1271 is suspended

[16277.797393] PM: Syncing filesystems ... done.
[16277.929870] PM: Preparing system for mem sleep
[16277.934509] Freezing user space processes ... (elapsed 0.02 seconds) done.
[16277.963470] Freezing remaining freezable tasks ... (elapsed 0.02 seconds) done.
[16277.994689] PM: Entering mem sleep
[16277.998565] Suspending console(s) (use no_console_suspend to debug)
[16278.242462] PM: suspend of devices complete after 236.060 msecs
[16278.243408] PM: late suspend of devices complete after 0.945 msecs
[16279.748199] Successfully put all powerdomains to target state

Resume the first EVM from Suspend by sending ping to it from the second EVM
Following is the screen shot shows how the Host is resuming from suspend mode, also the wl1271 is reconnecting to the WiFi network (by the WPA supplicant) and traffic resumes.

[16279.748840] PM: early resume of devices complete after 0.518 msecs
[16279.749237] platform iva.0: omap_voltage_scale: Already at the requestedrate 800000000
[16279.749237] platform mpu.0: omap_voltage_scale: Already at the requestedrate 1000000000
[16280.107391] PM: resume of devices complete after 358.428 msecs
[16280.157989] PM: Finishing wakeup.
[16280.161499] Restarting tasks ... done.

For more information on the commands we used:
Enabling system for hitting OFF By default, retention is the deepest sleep state attempted. To enable powerdomain transitions to off mode

# echo 1 > /tmp_debug/enable_off_mode

After a suspend or after some idle time, use the powerdomain transition stats to check that transitions to off-mode are happening

 # cat /tmp_debug/count

External Link

for more information use OMAP Power Management