Raspberry Pi A, Руководство пользователя, Страница: 131 / 314

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
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The BCM2835 multimedia processor at the heart of the Pi is a system-on-chip (SoC) design
split into two main parts: the graphics processor (GPU) and the central processor (CPU).
Simply put, the CPU handles all the day-to-day processing tasks while the GPU handles
drawing things on the screen, in both 2D and 3D.
Using
config.txt
, you can overclock one or both parts of the BCM2835. You can also
increase the speed at which the memory module—located on top of the chip in a package-
on-package (PoP) mounting format—operates.
Boosting the operating frequency of these components results in a small increase in the Pi’s
performance: an increase to the GPU’s clock frequency means that 3D graphics (such as
game graphics) will render at a faster pace, and video will be decoded quicker for smoother
playback; and increasing the CPU’s clock frequency will boost overall performance of the
device, as will increasing the memory’s frequency.
The reason the Pi isn’t provided with higher operating speeds in the first place is related to
the chip’s lifespan. The BCM2835 is rated by its manufacturer, Broadcom, to operate at a
speed of 700 MHz. Increasing the speed above this officially rated level may work, but it will
also have a deleterious effect on the lifespan of the chip. Unlike a desktop processor, SoC
designs rarely have much headroom for overclocking.
Overclocking Settings
If you’re willing to take the risk of breaking the Pi—a process known as bricking in embedded
device circles—for the sake of a small performance gain, there are settings in
config.txt
that can help. The following settings control performance of the Pi’s SoC:
❍
arm_freq
—Sets the core clock frequency of the CPU portion of the BCM2835, for a
boost in general-purpose performance. The default speed is 700 MHz.
❍
gpu_freq —Sets the clock frequency of the GPU portion of the BCM2835, for a boost
in graphics performance across all operations. The default speed is 250 MHz.
Additionally, you can adjust individual portions of the GPU’s hardware using the fol-
lowing options:
•
core_freq
—Sets the core clock frequency of the GPU, leaving the other frequen-
cies alone, to improve overall GPU performance. The default speed is 250 MHz.
•
h264_freq —Sets the clock frequency of the GPU’s hardware video decoder to
improve playback of H.264 video data. The default speed is 250 MHz.