Overclocking options in config.txt
NOTE: Setting any overclocking parameters to values other than those used by raspi-config may set a permanent bit within the SoC, making it possible to detect that your Pi has been overclocked. The specific circumstances where the overclock bit is set are if
force_turbo is set to
1 and any of the
over_voltage_* options are set to a value >
0. See the blog post on Turbo Mode for more information.
The kernel has a CPUFreq driver with the "powersave" governor enabled by default, switched to "ondemand" during boot, when raspi-config is installed. With "ondemand" governor, CPU frequency will vary with processor load. You can adjust the minimum values with the
*_min config options or disable dynamic clocking by applying a static scaling governor ("powersave" or "performance") or with
force_turbo=1. For more information see this section of the documentation.
Overclocking and overvoltage will be disabled at runtime when the SoC reaches
temp_limit (see below), which defaults to 85°C, in order to cool down the SoC. You should not hit this limit with Raspberry Pi Models 1 and 2, but you are more likely to with Raspberry Pi 3 and Raspberry Pi 4B. For more information see this section of the documentation. Overclocking and overvoltage are also disabled when an undervoltage situation is detected.
|arm_freq||Frequency of the ARM CPU in MHz.|
|core_freq||Frequency of the GPU processor core in MHz, influences CPU performance because it drives the L2 cache and memory bus; the L2 cache benefits only Pi Zero/Pi Zero W/ Pi 1, there is a small benefit for SDRAM on Pi 2/Pi 3. See section below for use on the Pi 4.|
|h264_freq||Frequency of the hardware video block in MHz; individual override of the
|isp_freq||Frequency of the image sensor pipeline block in MHz; individual override of the
|v3d_freq||Frequency of the 3D block in MHz; individual override of the
|hevc_freq||Frequency of the High Efficiency Video Codec block in MHz; individual override of the
|sdram_freq||Frequency of the SDRAM in MHz. SDRAM overclocking on Pi 4B is not currently supported|
|over_voltage||CPU/GPU core upper voltage limit. The value should be in the range [-16,8] which equates to the range [0.95V,1.55V] ([0.8,1.4V] on RPi 1) with 0.025V steps. In other words, specifying -16 will give 0.95V (0.8V on RPi 1) as the maximum CPU/GPU core voltage, and specifying 8 will allow up to 1.55V (1.4V on RPi 1). For defaults see table below. Values above 6 are only allowed when
|over_voltage_sdram_c||SDRAM controller voltage adjustment. [-16,8] equates to [0.8V,1.4V] with 0.025V steps.|
|over_voltage_sdram_i||SDRAM I/O voltage adjustment. [-16,8] equates to [0.8V,1.4V] with 0.025V steps.|
|over_voltage_sdram_p||SDRAM phy voltage adjustment. [-16,8] equates to [0.8V,1.4V] with 0.025V steps.|
|force_turbo||Forces turbo mode frequencies even when the ARM cores are not busy. Enabling this may set the warranty bit if
|initial_turbo||Enables turbo mode from boot for the given value in seconds, or until cpufreq sets a frequency. For more information see here. The maximum value is
|arm_freq_min||Minimum value of
|core_freq_min||Minimum value of
|gpu_freq_min||Minimum value of
|h264_freq_min||Minimum value of
|isp_freq_min||Minimum value of
|v3d_freq_min||Minimum value of
|hevc_freq_min||Minimum value of
|sdram_freq_min||Minimum value of
|over_voltage_min||Minimum value of
|temp_limit||Overheat protection. This sets the clocks and voltages to default when the SoC reaches this value in degree Celsius. Values over 85 are clamped to 85.|
|temp_soft_limit||3A+/3B+ only. CPU speed throttle control. This sets the temperature at which the CPU clock speed throttling system activates. At this temperature, the clock speed is reduced from 1400MHz to 1200MHz. Defaults to
This table gives the default values for the options on various Raspberry Pi Models, all frequencies are stated in MHz.
|Option||Pi 0/W||Pi1||Pi2||Pi3||Pi3A+/Pi3B+||Pi4/CM4||Pi 400|
This table gives defaults for options that are the same across all models.
|over_voltage||0 (1.35V, 1.2V on RPi 1)|
The firmware uses Adaptive Voltage Scaling (AVS) to determine the optimum CPU/GPU core voltage in the range defined by
|Pi 4, Pi400, CM4||0||0.88V|
Specific to Pi 4, Pi 400 and CM4
The minimum core frequency when the system is idle must be fast enough to support the highest pixel clock (ignoring blanking) of the display(s). Consequently,
core_freq will be boosted above 500 MHz if the display mode is 4Kp60.
- Overclocking requires the latest firmware release.
- The latest firmware automatically scales up the voltage if the system is overclocked. Manually setting
over_voltagedisables automatic voltage scaling for overclocking.
- It is recommended when overclocking to use the individual frequency settings (
v3d_freqetc) rather than
gpu_freqbecause the maximum stable frequency will be different for ISP, V3D, HEVC etc.
- The SDRAM frequency is not configurable on Raspberry Pi 4.
By default (
force_turbo=0) the "On Demand" CPU frequency driver will raise clocks to their maximum frequencies when the ARM cores are busy and will lower them to the minimum frequencies when the ARM cores are idle.
force_turbo=1 overrides this behaviour and forces maximum frequencies even when the ARM cores are not busy.
Sets a bit in the OTP memory (one time programmable) that prevents the device from being overvoltaged. This is intended to lock the device down so the warranty bit cannot be set either inadvertently or maliciously by using an invalid overvoltage.
On Pi 2/Pi 3, setting this flag will disable the GPU from moving into turbo mode, which it can do in particular load cases.
The GPU core, CPU, SDRAM and GPU each have their own PLLs and can have unrelated frequencies. The h264, v3d and ISP blocks share a PLL. For more information see here.
To view the Pi's current frequency in KHz, type:
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq. Divide the result by 1000 to find the value in MHz. Note that this frequency is the kernel requested frequency, and it is possible that any throttling (for example at high temperatures) may mean the CPU is actually running more slowly than reported. An instantaneous measurement of the actual ARM CPU frequency can be retrieved using the vcgencmd
vcgencmd measure_clock arm. This is displayed in Hertz.
Monitoring core temperature
To view the Pi's temperature, type
cat /sys/class/thermal/thermal_zone0/temp. Divide the result by 1000 to find the value in degrees Celsius. Alternatively, there is a vcgencmd,
vcgencmd measure_temp that interrogates the GPU directly for its temperature.
Whilst hitting the temperature limit is not harmful to the SoC, it will cause CPU throttling. A heatsink can help to control the core temperature and therefore performance. This is especially useful if the Pi is running inside a case. Airflow over the heatsink will make cooling more efficient.
With firmware from 12th September 2016 or later, when the core temperature is between 80'C and 85'C, a warning icon showing a red half-filled thermometer will be displayed, and the ARM cores will be throttled back. If the temperature exceeds 85'C, an icon showing a fully-filled thermometer will be displayed, and both the ARM cores and the GPU will be throttled back.
For the Raspberry Pi 3 Model B+, the PCB technology has been changed to provide better heat dissipation and increased thermal mass. In addition, a soft temperature limit has been introduced, with the goal of maximising the time for which a device can "sprint" before reaching the hard limit at 85°C. When the soft limit is reached, the clock speed is reduced from 1.4GHz to 1.2GHz, and the operating voltage is reduced slightly. This reduces the rate of temperature increase: we trade a short period at 1.4GHz for a longer period at 1.2GHz. By default, the soft limit is 60°C, and this can be changed via the
temp_soft_limit setting in config.txt.
See the page on warning icons for more details.
It is essential to keep the supply voltage above 4.8V for reliable performance. Note that the voltage from some USB chargers/power supplies can fall as low as 4.2V. This is because they are usually designed to charge a 3.7V LiPo battery, not to supply 5V to a computer.
To monitor the Pi's PSU voltage, you will need to use a multimeter to measure between the VCC and GND pins on the GPIO. More information is available in power.
If the voltage drops below 4.63V (+-5%), recent versions of the firmware will show a yellow lightning bolt symbol on the display to indicate a lack of power, and a message indicating the low voltage state will be added to the kernel log.
See the page on warning icons for more details.
Most overclocking issues show up immediately with a failure to boot. If this occurs, hold down the
shift key during the next boot. This will temporarily disable all overclocking, allowing you to boot successfully and then edit your settings.
This article uses content from the eLinux wiki page RPiconfig, which is shared under the Creative Commons Attribution-ShareAlike 3.0 Unported license