Hardware Reference
In-Depth Information
he irst ile,
arm128_start.elf
, is conigured to split the memory down the middle, with
128 MB available to the BCM2835's ARM CPU and 128 MB available to the VideoCore
IV GPU.
he second and third iles gradually reduce the amount of memory available to the GPU.
arm192_start.elf
gives 192 MB to the CPU and 64 MB to the GPU, while
arm224_
start.elf
gives 224 MB to the CPU and 32 MB to the GPU. By telling the Pi to use these
iles, you can increase the amount of memory available for general-purpose computing.
Applications that do heavy graphics work, such as 3D games and high-deinition video playback
software, typically need 128 MB of memory for the GPU. Reducing this can result in a dramatic
drop in performance.
WARNING
Most general-purpose distributions work on a 192 MB/64 MB split, but you can free up
more memory for programs by forcing the Pi to use the 224 MB/32 MB split. his can
improve general-purpose performance without the risks associated with overclocking the Pi.
To change how the memory is apportioned, simply delete
start.elf
from the
/boot
directory and copy one of the three other versions in its place. Make sure you rename the ile
to
start.elf
, or the Pi won't boot. he easiest way to achieve this is to type the following
at the terminal:
sudo cp /boot/arm224_start.elf /boot/start.elf
When you next reboot the Pi, it will have more memory available to the ARM CPU. To check
the amount of memory available, type
free
at the terminal. To change to another memory
split, simply repeat the preceding command with a diferent version of
start.elf
as the
source ile:
arm_192_start.elf
or
arm128_start.elf
.
Software Settings—cmdline txt
In addition to
config.txt
, which controls various features of the Pi's hardware, there's
another important text ile in the
/boot
directory:
cmdline.txt
(see Figure 6-3). his ile
contains what is known as the
kernel mode line
—options passed to the Linux kernel as the Pi
boots up.
