config.txt - Overclocking options

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 latest kernel has a cpufreq kernel driver with the "ondemand" governor enabled by default. It has no effect if you have no overclock settings, but if you overclock, the CPU frequency will vary with processor load. Non-default values are only used when required, according to the governor. You can adjust the minimum values with the *_min config options, or disable dynamic clocking (and force overclocking) with force_turbo=1. For more information see here.

Overclocking and overvoltage will be disabled at runtime when the SoC reaches 85°C in order to cool it down. You should not hit this limit on Raspberry Pi models 1 or 2, but it is more likely with the Raspberry Pi 3. For more information see here. Overclocking and overvoltage are also disabled when an undervoltage situation is detected.

Overclocking options

Option Description
arm_freq Frequency of the ARM CPU in MHz. The default value is 1000 for the Pi Zero and Pi Zero W, 700 for Pi 1, 900 for Pi 2, 1200 for the Pi 3.
gpu_freq Sets core_freq, h264_freq, isp_freq, and v3d_freq together. On Pi 1/Pi 2 the default value is 250 for all items, on Pi 3/Pi Zero /Pi Zero W core_freq defaults to 400 and h264_freq, isp_freq and v3d_freqdefault to 300.
core_freq Frequency of the GPU processor core in MHz. It has an impact on CPU performance because it drives the L2 cache and memory bus. The default value is 250 for the Pi 1/Pi 2 and 400 for the Pi 3 and Pi Zero and Pi Zero W. Note that the L2 cache benefits only the Pi Zero/Pi Zero W and Pi 1, but there is a small benefit for SDRAM on the Pi 2/Pi 3.
h264_freq Frequency of the hardware video block in MHz. Individual override of the gpu_freq setting.
isp_freq Frequency of the image sensor pipeline block in MHz. Individual override of the gpu_freq setting.
v3d_freq Frequency of the 3D block in MHz. Individual override of the gpu_freq setting.
sdram_freq Frequency of the SDRAM in MHz. The default value is 400 for the Pi 1 and Pi 2, 450 on the Pi 3, Pi Zero and Pi Zero W.
over_voltage CPU/GPU core voltage adjustment. [-16,8] equates to [0.8V,1.4V] with 0.025V steps. In other words, specifying -16 will give 0.8V as the GPU/core voltage, and specifying 8 will give 1.4V. For defaults see table below. Values above 6 are only allowed when force_turbo is specified: this sets the warranty bit if over_voltage_* is also set.
over_voltage_sdram Sets over_voltage_sdram_c, over_voltage_sdram_i, and over_voltage_sdram_p together.
over_voltage_sdram_c SDRAM controller voltage adjustment. [-16,8] equates to [0.8V,1.4V] with 0.025V steps. The default value is 0 (1.2V).
over_voltage_sdram_i SDRAM I/O voltage adjustment. [-16,8] equates to [0.8V,1.4V] with 0.025V steps. The default value is 0 (1.2V).
over_voltage_sdram_p SDRAM phy voltage adjustment. [-16,8] equates to [0.8V,1.4V] with 0.025V steps. The default value is 0 (1.2V).
force_turbo Forces turbo mode frequencies even when the ARM cores are not busy. Enabling this may set the warranty bit if over_voltage_* is also set.
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 default value is 0, maximum value is 60.
arm_freq_min Minimum value of arm_freq used for dynamic frequency clocking. The default value is 700 for the Pi Zero/Pi 1, 600 for the Pi 2/Pi 3.
core_freq_min Minimum value of core_freq used for dynamic frequency clocking. The default value is 250.
gpu_freq_min Minimum value of gpu_freq used for dynamic frequency clocking. The default value is 250.
h264_freq_min Minimum value of h264_freq used for dynamic frequency clocking. The default value is 250.
isp_freq_min Minimum value of isp_freq used for dynamic frequency clocking. The default value is 250.
v3d_freq_min Minimum value of v3d_freq used for dynamic frequency clocking. The default value is 250.
sdram_freq_min Minimum value of sdram_freq used for dynamic frequency clocking. The default value is 400.
over_voltage_min Minimum value of over_voltage used for dynamic frequency clocking. The default value is 0.
temp_limit Overheat protection. This sets the clocks and voltages to default when the SoC reaches this value in Celsius. The default value is 85. Values over 85 are clamped to 85.

This table describes the overvoltage settings for the various Pi models. The firmware uses Adaptive Voltage Scaling (AVS) to determine the optimum voltage to set. Note that for each integer rise in over_voltage, the voltage will be 25mV higher.

Version Default Overvoltage Setting
Pi 1 1.2V 0
Pi 2 1.2-1.3125V 0
Pi 3 1.2-1.3125V 0
Pi Zero 1.35V 6

force_turbo

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.

never_over_voltage

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 the warranty bit cannot be set either inadvertently or maliciously by using an invalid overvoltage.

disable_auto_turbo

On the Pi 2/Pi 3, setting this flag will disable the GPU from moving into turbo mode, which it can do in particular load cases.

Clocks relationship

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, type: cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq. Divide the result by 1000 to find the value in MHz.

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 Celsius.

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. A suitable heatsink is the self-adhesive BGA (ball-grid-array) 14x14x10 mm heatsink available from RS Components.

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.

See the page on warning icons for more details.

Monitoring voltage

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.

See the page on warning icons for more details.

Overclocking problems

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