Skip to content

Power management (MX-4)

Overview of Suspend Design⚓︎

The MX-4 platform features two CPUs:

  • The main CPU runs Linux and user applications.
  • The co-CPU (or coprocessor) serves multiple purposes (PMIC, GPIO chip, analog inputs, hardware watchdog, etc.).

The main CPU initiates sleep/suspend mode, while wake-up can be triggered by either CPU, depending on the wake-up source (see Wakeup).

During sleep/suspend mode:

  • The main CPU powers off most peripherals.
  • The co-CPU runs on internal low-power RC (32 kHz) and performs cyclic sleep.
  • 3.3 V and 5 V power off, specific to different MX-4 platforms.

Warning: The following peripherals lose power and need re-initialization after wakeup:

  • SD card (unmount before sleep, re-mount after wake-up)
  • WiFi
  • UART
  • CAN (T30 FR can optionally power off/on the CAN transceivers)
  • Ethernet
  • Flexray

Enter sleep⚓︎

A script, /opt/hm/go_to_sleep.sh, provided by Host Mobility, facilitates entering sleep/suspend mode:

Usage: go_to_sleep.sh options (t:hdcCnsaD)
                -t <time in seconds> - Setup wakealarm (rtc)
                -d - Disable wake on DIGITAL-IN-2
                -a - Disable wake on START-SIGNAL
                -l <mV level> - START-SIGNAL wake-up volt level
                -c - Wake on CAN
                -n - Will renew dhcp lease
                -C - Disable suspend CAN for quicker wakeup-time"
                -s - Will suspend modem (turn off), Will not restore on wake up
                -D <time in seconds> - Will enter deep sleep.
                        Power to main CPU will be cut after specified time and it
                        will restart with a cold reboot on wake up. The application
                        is responsible of shutting down the system properly before
                        the power is cut.
                -p <wake up mask> - Mask to enable/disable wakeup sources
                -h - Print this text

Wakeup⚓︎

The MX-4 platform supports a range of wake-up sources (see below), although not all MX-4 variants support each of the wake-up sources.

  • Digital Inputs (DIGITAL-IN-2 is enabled by default as a wake-up source)
  • Analog Inputs
  • Wake on CAN
  • Wake on RTC (wake up after x seconds)
  • Wake on RING (call/SMS to modem) – Not yet supported in software
  • Wake on Accelerometer – Not yet supported in software
Wake on Digital Inputs⚓︎

By default, DIGITAL-IN-2 (rising edge) is enabled as a wake-up source, mostly due to historical reasons. To disable it, run go_to_sleep.sh with the -d option.

On some platforms, DIGITAL-IN-2 is the only digital input capable of waking up the system.

For a list of supported digital inputs as wakeup sources, see .

Note: If -d option is not specified, it will always set bit 4 in the wake-up mask, regardless of what you passed.

Note: If -d option is specified with -t or without any other wake-up flag (use WAKE_UP_SRC_MODEM_RING bitmask or set -l to a voltage level higher than input voltage), the system will reboot itself. See Reset Cause.

To enable different wake-up sources and set the edge, use the -p option with a bitmask (see wake up cause.

Wake on Analog Inputs⚓︎

Analog inputs as wake-up sources are not managed by go_to_sleep.sh.

All analog inputs have four sysfs files associated with them. For example, if we take input voltage:

[Sysfs files and their purposes]

  • input_voltage reads the value of input voltage.
  • input_voltage_calibration_u calibrates the input for component tolerances.
  • input_voltage_threshold_high enables wake on a high-level threshold.
  • input_voltage_threshold_low enables wake on a low-level threshold.

Examples of wake-up setup:

# Wake up system from sleep/suspend if input voltage is above 16 V
root@mx4-vcc-1000000:~# echo 16000 > /opt/hm/pic_attributes/input_voltage_threshold_high

# Wake up system from sleep/suspend if input voltage is below 12 V
root@mx4-vcc-1000000:~# echo 12000 > /opt/hm/pic_attributes/input_voltage_threshold_low

# Wake up system from sleep/suspend if input voltage is in the range of 12-16 V
root@mx4-vcc-1000000:~# echo 16000 > /opt/hm/pic_attributes/input_voltage_threshold_high
root@mx4-vcc-1000000:~# echo 12000 > /opt/hm/pic_attributes/input_voltage_threshold_low


# Write 0 to both threshold files to disable that specific input as a wake-up source
root@mx4-vcc-1000000:~# echo 0 > /opt/hm/pic_attributes/input_voltage_threshold_high
root@mx4-vcc-1000000:~# echo 0 > /opt/hm/pic_attributes/input_voltage_threshold_low
User setup for analog wake-up sources is required before calling go_to_sleep.sh. See Enter sleep.

Wake on CAN⚓︎

Wake on CAN isn't supported on all MX-4 platforms. Contact Host Mobility support for compatibility information.

Enable Wake on CAN by passing -c to go_to_sleep.sh (see Enter sleep). However, before doing this, specific CAN buses should be enabled as wake-up sources.

By default, all CAN buses will trigger a wakeup if there is traffic on them and -c is passed to go_to_sleep.sh. For T30 FR it is possible to wake up on single specific CAN frame (can-xcvr).

GPIOs are used to set this up:

root@mx4-vcc-1000000:~# cat /sys/kernel/debug/gpio | grep -i wakeup
 gpio-58  (P169 - CAN0-WAKEUP  ) out lo
 gpio-59  (P171 - CAN1-WAKEUP  ) out lo
 gpio-60  (P173 - CAN2-WAKEUP  ) out lo
 gpio-61  (P175 - CAN3-WAKEUP  ) out lo
 gpio-62  (P177 - CAN4-WAKEUP  ) out lo
 gpio-63  (P179 - CAN5-WAKEUP  ) out lo

To disable wake-up for a specific bus, write a 1 to that GPIO's value.

# Disable wakeup on CAN0
root@mx4-vcc-1000000:~# echo 1 > /sys/class/gpio/gpio58/value

Wake up cause⚓︎

Read which signal that made the platform to wake up. See wake up cause.

Deep sleep⚓︎

Deep sleep mode puts the coprocessor to sleep while cutting the power rail to the main CPU. Upon wakeup, a cold reboot occurs instead of a fast resume, trading off for lower consumption during the suspended state.

Wake-up sources available from deep sleep vary across different platforms.

Enter deep sleep by passing the -D option to go_to_sleep.sh. See Enter sleep.

Note: CT and CT GL do not support Deep sleep

Shutdown⚓︎

Not all MX-4 platforms support this mode. Contact Host Mobility support for information on compatibility.

The MX-4 shutdown/cutoff state turns the system off with close to zero power consumption:

# Cutoff in 60 seconds
root@mx4-vcc-1000000:~# echo 60 > /opt/hm/pic_attributes/ctrl_on_4v

In this example, within 60 seconds, the system will cut the 4V power and restart only if Start signal is LOW.

Before these 60 seconds elapse, ensure the application finishes and runs poweroff to shut down Linux.