Hardware Reference
In-Depth Information
have a separate Raspberry-Pi-specific Linux kernel source tree, and it is
possible that the Raspberry Pi Foundation will stop providing new prebuilt
kernel images as a result.
This is just speculation, though, because while the Raspberry Pi Foundation
has indicated a desire for merging its patches into the upstream Linux ker-
nel tree, and there are various kernel hackers working toward this goal, it
has not yet happened. To date, the Foundation has not given any indication
that it will stop making prebuilt kernel images. This should not be too big of
a problem if it does happen, because the Linux distributions will easily be
able to produce prebuilt Raspberry-Pi-specific Linux kernel images that
they maintain from the upstream “Linus” source tree.
We point this out only so that if you are reading this topic at a future time
when this has indeed occurred and you are not seeing recently updated
prebuilt kernel images in their GitHub firmware repository, you might have
an idea why.
Split Memory Between the GPU and
Linux Userspace
HACK 24
The performance that you get from your Raspberry Pi is tightly coupled
to the amount of memory that you allocate to its core components. Be-
cause this isn't a system you can just drop more RAM into, you should
consider the needs of your project and the best way to split the available
memory.
In the embedded hardware universe, memory is almost always a precious and scant
commodity. The performance of the system is usually tightly coupled to the amount
of present (and accessible) memory. Additionally, most embedded systems do not
have any user-serviceable method to increase the amount of physical memory, and
the Raspberry Pi is no different.
When the Raspberry Pi Model B was first released, it came with 256 MiB of memory
(either Hynix MobileDDR2 or Samsung Mobile DRAM, depending on when it was pro-
duced). The memory rests physically on top of the Broadcom media processor in the
BCM2835 system-on-chip. This is known as
package on package
(PoP). PoP allows
for an embedded system to combine multiple ball grid array (BGA) packages in a
vertical stack.
The Raspberry Pi system-on-chip uses a mixed logic-memory stack, which is useful
to save space and allows the hardware vendor to choose from a wide range of com-
patible options (and helps them to keep costs down). This design decision allowed
