Search by Tags

Suspend/Resume (Linux)

 

Compare with Revision


Subscribe for this article updates

Suspend/Resume on NVIDIA Tegra

The NVIDIA Tegra T20 and T30 support Low Power modes (LP). Currently LP1 is supported which means CPU is put into a sleep mode and RAM is in self-refresh mode. LP1 mode draws around 180mW on a Colibri T20 512 MB on the Iris Carrier Board)

root@colibri_t20:~# echo mem > /sys/power/state

In order to wake the system up again, the SODIMM PIN 45 (Evaluation Board: Pin 4 on X8, Iris: Pin 20 on X16) need to be pulled up or down (depending on previous state).

The suspend mode can be selected using /sys/power/suspend/mode. But currently only LP1 is supported.

Note: Check the release notes for possible limitations.

Suspend/Resume on NXP Vybrid

Disable Ethernet PHY

The Ethernet PHY used on our Vybrid based modules has an errata which does not allow the PHY to power down and wake-up reliable. Therefor, suspend mode for the Ethernet PHY has been disabled by default (by this commit).

For low-power applications not using Ethernet, it is recommended to set the PHY in power-down mode in U-Boot and disable the PHY driver in Linux. To disable PHY control from Linux either disable the Ethernet and PHY driver in the kernel configuration or remove the corresponding device tree node (e.g. set the status property of the fec node to disabled see Device Tree Customization).

Use the following U-Boot command to disable the Ethernet PHY:

Colibri VFxx # mii write 0 0 0x3800​

Extend the bootcmd to disable the Ethernet PHY by default:

Colibri VFxx # setenv bootcmd "mii write 0 0 0x3800 && ${bootcmd}"
Colibri VFxx # saveenv

Standby mode

The standby sleep state puts the Vybrid SoC in STOP mode. The SoC can be woken from standby through any peripheral interrupt. However, currently wake-up capabilities have been implemented and tested only for some peripheral drivers, namely GPIO, SNVS RTC and UART driver.

Entering standby mode:

# echo standby > /sys/power/state

Suspend-to-RAM mode

The mem sleep state (Suspend-to-RAM) uses Vybrid's LPSTOP2 mode. This mode powergates most parts of the SoC expect some peripherals such as Wake-Up controller (WKPU) or LP RTC. The main memory (DDR3) is put into self-refresh mode. The SoC can be woken from mem sleep state through wake-up GPIOs or internal SNVS RTC.

Entering in suspend to mem mode:

# echo mem > /sys/power/state

Or

# systemctl suspend

Note:

  • Suspend to mem mode is supported since V1.2A module revision.
  • There are few systemd services which are used as a work around for a known issue with USB host not working after using LPSTOP suspend mode. To make sure USB is working on resume from a suspend to mem, use systemctl suspend to initiate suspend to mem.

GPIO Wake-Up

By default SODIMM PIN 45(Evaluation Board: Pin 4 on X8, Iris: Pin 20 on X16) is used as wake-up GPIO. Toggle SODIMM PIN 45.

RTC Wake-Up using internal SNVS RTC

The below example sets the timeout(in Sec) to wakeup from standby/suspend to mem mode.

# echo +10 > /sys/class/rtc/rtc1/wakealarm

UART Wake-up

The below example enables ttyLP0 as wake-up source.

# echo enabled > /sys/class/tty/ttyLP0/power/wakeup

Note: UART wake-up is only supported for standby mode.