Game Development Reference
In-Depth Information
5. Then, the kernel image reads
config.txt
,
cmdline.txt
, and
bcm2835.dtb
.
6. If the
.dtb
file exists, it is loaded at 0 × 100 and the kernel is loaded at
0 × 8000 in memory.
7. The kernel image is the first binary that runs on the ARM CPU, and it can be
compiled with the custom support for a specific hardware.
8.
The operating system starts to load.
All the source code in Stages 1 to 3 are closed source and protected by Broadcom.
These closed source files are compiled and released by Broadcom only. You can
update them on your SD card by running a firmware upgrade in Raspbian, which
is covered later.
The
kernel.img
file connects the application to the hardware. Any computer with
an operating system has a kernel of some sort. It is possible to compile your own
kernel in Linux, and it might be the first file that you might want to amend yourself.
This allows you to change the boot screen, load custom drivers, or perform other
tasks that you might need. This is an advanced task and is not covered in this topic.
Other capabilities
The BCM2835 processor also has dedicated audio hardware together with audio
and video encoding/decoding. This allows the Pi to playback HD (MPEG-4) content
such as videos or games. You can buy additional encoder/decoder licenses for extra
functionality like MPEG-2 used in DVD video encoding and VC-1 that is used by
Microsoft's WMV formats. The SD card is also directly interfaced by the Broadcom
chip using the dedicated hardware inputs/outputs and interrupts.
All that dedicated hardware means that while some sections of the chip are fully
utilized, the ARM CPU will be idle or hardly used. This will allow you to compute
other transactions synchronously, and this is what makes the Raspberry Pi truly a
unique, single board, credit-card-sized computer!
Hardware limitations
All this hardware crammed into one tiny space has its drawbacks. Some are
deliberate and others are not. You should consider that these are theoretical
calculations and that the real-world performance may vary. Usually, it is
slower than the theoretical estimation.
