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C H A P T E R 7
A D V A N C E D R A S P B E R R Y P I C O N F I G U R A T I O N
117
If you want to eke a little more performance out of your Pi, there is a way to potentially boost
this upper limit: a process known as
overvoltage or overvolting . The Pi’s BCM2835 system-on-
chip processor and the associated memory module usually run at 1.2 V. It’s possible, although
potentially inadvisable, to override this default and force the components to run at higher or
lower voltages. Boosting the voltage means boosting the signal within the chip, making it
more likely to hit higher speeds—it also means that the chip runs hotter, reducing its lifes-
pan dramatically compared to overclocking alone.
WARNING
Setting any of the voltage options in
config.txt
causes a fuse within the BCM2835 to trip
in a way that cannot be reset. It’s a foolproof way to tell if someone has been attempting to
overclock the chip outside its rated specifications, and
renders your warranty null and void —
even if the cause of failure is unrelated to overclocking. If you return a Pi for replacement under
warranty and the fuse is tripped,
it will not be replaced . Do not attempt to overvolt a Pi that you
cannot afford to replace yourself.
Unlike the previously described settings, which are provided in
config.txt
as absolute
values, the voltage adjustment is carried out using values relative to the Pi’s stock 1.2 V set-
ting. For each whole number above zero, the voltage is increased by 0.025 V from stock. For
each whole number below zero, the voltage is decreased by 0.025 V from stock.
The voltage adjustment settings have upper and lower limits of 8 and -16, equivalent to 0.2
V above stock voltage or 1.4 V absolute and 0.4 V below stock voltage or 0.8 V absolute. The
voltage must be adjusted in whole numbers, and it cannot be adjusted below 0.8 V (-16) or
above 1.4 V (8.)
The following settings are accessible from
config.txt
:
❍
over_voltage —Adjusts the BCM2835’s core voltage. Values are given as a whole
number (an integer) corresponding to 0.025 V above or below the default value (
0
,)
with a lower limit of
-16
and an upper limit of
8
.
❍
over_voltage_sdram —Adjusts the voltage given to the memory chip on the Pi. As with
over_voltage
, values are given as a whole number corresponding to 0.025 V above or
below the stock (
0
,) with a lower limit of
-16
and an upper limit of
8
. Additionally, you
can adjust voltages for individual memory components using the following options:
•
over_voltage_sdram_c —Adjusts the voltage given to the memory controller.
Acceptable values are the same as with
over_voltage_sdram
.
•
over_voltage_sdram_i —Adjusts the voltage given to the memory’s input/output
(I/O) system. Acceptable values are the same as with
over_voltage_sdram
.
•
over_voltage_sdram_p
—Adjusts the voltage given to the memory’s physical layer
(PHY) components. Acceptable values are the same as with
over_voltage_sdram
.