DVFS User Guide

1. Overview

This document introduces how to use the DVFS function on the SigmaStar platform. DVFS (Dynamic voltage and frequency scaling) refers to dynamically adjusting the CPU frequency and voltage according to actual needs to achieve the purpose of improving performance or saving energy consumption.

2. Configuration Instructions

In Linux, you need to enable the following configuration to enable the DVFS function:

SSTAR_CPU_FREQ:

Symbol: SSTAR_CPU_FREQ [=y]
Type  : tristate
Defined at drivers/sstar/cpufreq/Kconfig:1
  Prompt: Sstar CPU frequency scaling driver
  Depends on: SSTAR_DRIVERS [=y]
  Location:
    -> Device Drivers
      -> Sstar SoC platform drivers (SSTAR_DRIVERS [=y])

SSTAR_VOLTAGE_IDAC_CTRL:

Symbol: SSTAR_VOLTAGE_IDAC_CTRL [=y]
Type  : bool
Defined at drivers/sstar/voltage_idac/Kconfig:1
  Prompt: Sstar Voltage IDAC Control
  Depends on: SSTAR_DRIVERS [=y] && SSTAR_GPIO [=y] && !SSTAR_VOLTAGE_CTRL [=n]
  Location:
    -> Device Drivers
      -> Sstar SoC platform drivers (SSTAR_DRIVERS [=y])
 -> Sstar Voltage Control (SSTAR_VOLTAGE_CTRL [=n])

SSTAR_VOLTAGE_IDAC_STEP_BY_STEP:

Symbol: SSTAR_VOLTAGE_IDAC_STEP_BY_STEP [=y]
Type  : bool
Defined at drivers/sstar/voltage_idac/Kconfig:6
  Prompt: Sstar Voltage IDAC Control Step By Step
  Depends on: SSTAR_DRIVERS [=y] && SSTAR_VOLTAGE_IDAC_CTRL [=y] ontrol RL [=n]
  Location:
    -> Device Drivers
      -> Sstar SoC platform drivers (SSTAR_DRIVERS [=y])
 -> Sstar Voltage Control (SSTAR_VOLTAGE_CTRL [=n])
 -> Sstar Voltage IDAC Control (SSTAR_VOLTAGE_IDAC_CTRL [=y])

After enabling the above configuration, Linux will generate the following paths and files:

/ # ls -l /sys/devices/system/cpu/cpufreq/
total 0
-rw-r--r--    1 root     root          4096 Jan  1 00:02 cpufreq_testout
drwxr-xr-x    3 root     root             0 Jan  1 00:02 policy0
-rw-r--r--    1 root     root          4096 Jan  1 00:02 rosc_out
-rw-r--r--    1 root     root          4096 Jan  1 00:02 rosc_threshold
-r--r--r--    1 root     root          4096 Jan  1 00:02 sidd_out
-rw-r--r--    1 root     root          4096 Jan  1 00:02 temp_adjust_threshold_hi
-rw-r--r--    1 root     root          4096 Jan  1 00:02 temp_adjust_threshold_lo
-r--r--r--    1 root     root          4096 Jan  1 00:02 temp_out

/ # ls -l /sys/devices/system/voltage/cpu_power/
total 0
drwxr-xr-x    2 root     root             0 Jan  1 00:05 power
-rw-r--r--    1 root     root          4096 Jan  1 00:05 scaling_voltage
lrwxrwxrwx    1 root     root             0 Jan  1 00:05 subsystem -> ../../../../bus/voltage
-rw-r--r--    1 root     root          4096 Jan  1 00:05 uevent
-r--r--r--    1 root     root          4096 Jan  1 00:05 vid_gpio_map
-r--r--r--    1 root     root          4096 Jan  1 00:05 voltage_available
-rw-r--r--    1 root     root          4096 Jan  1 00:05 voltage_current

3. Related commands

3.1. Check CPU frequency

/ # cat /sys/devices/system/cpu/cpufreq/cpufreq_testout
1500000000

The unit of 1500000000 is Hz, which means the current CPU frequency is 1.5GHz.

3.2. Set CPU frequency

/ # echo userspace > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
/ # echo 1200000 > /sys/devices/system/cpu/cpufreq/policy0/scaling_setspeed

If you want to set the CPU frequency manually, you need to set the frequency adjustment policy of cpufreq to userspace first, and then set the CPU frequency. In the above command, the unit of 1200000 is KHz, which means setting the CPU frequency to 1.2GHz.

3.3. Check CPU voltage

/ # cat /sys/devices/system/voltage/cpu_power/voltage_current
900
    VOLTAGE_DEMANDER_INIT           -
    VOLTAGE_DEMANDER_CPUFREQ        900
    VOLTAGE_DEMANDER_TEMPERATURE    -
    VOLTAGE_DEMANDER_USER           -

The unit of 900 is mV, which means the current CPU voltage is 900mV.

3.4. Check CPU temperature

/ # cat /sys/devices/system/cpu/cpufreq/temp_out
Temp = 27

The unit of 27 is Celsius, which means the current CPU temperature is 27 degrees Celsius.