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mbedded systems usually fall
into one of two categories:
those that require hard real-time
performance and those that don’t.
In the past, we had to pick our
poison-the performance of our “go
to” real-time operating system or the
rich feature set of our favorite Linux
distribution-and then struggle with its
shortcomings.
Today, embedded developers no
longer need to choose between the
two. Asymmetric multiprocessing
(AMP) offers the best of both worlds.
Several modern system-on-chip (SoC)
product offerings integrate multiple
CPUs, a broad variety of standard
I/O peripherals and programmable
logic. The Xilinx® Zynq-7000®
All Programmable SoC family, for
example, includes a dual-core ARM®
Cortex™-A9, standard peripherals
(such as Gigabit Ethernet MACs, USB,
DMA, SD/MMC, SPI and CAN) and a
large programmable logic array.
We can use these SoC products
as the basis of a Linux/RTOS AMP
system that provides considerable
flexibility. In many ways, the typical
AMP configuration is similar to a PCI-
based system, with the Linux domain
functioning as the host, the RTOS
domain functioning as an adapter, and
one or more shared memory regions
used for communication between the
two domains.
Unlike PCI, however, an AMP
configuration can more conveniently-
and dynamically-assign resources
(both the standard peripherals and
custom logic) to one domain or the
other. In addition, a Linux/RTOS AMP
system can dynamically reconfigure
programmable logic based on runtime
requirements, such as the presence or
absence of various external devices.
This level of flexibility is often coupled
with concerns about complexity and
the degree of difficulty involved in
bringing up an AMP system. Rest
assured that the Linux development
community has introduced many
features into the kernel that greatly
simplify AMP configuration and use.
LINUX MULTIPROCESSING
IN A NUTSHELL
With respect to multiprocessing, the
Linux kernel comes in two flavors:
the uniprocessor (UP) kernel and
the symmetric multiprocessor (SMP)
kernel. The UP kernel can only run
on a single core, regardless of the
number of available cores. AMP
systems can incorporate two or more
instances of the uniprocessor kernel.
The SMP kernel, however, can run on
one core or simultaneously on multiple
cores (Figure 1). An optional kernel
command line parameter controls the
number of cores used by the SMP
kernel following system initialization.
Once the kernel is running, various
command line utilities control the
number of cores assigned to the
E
AMP up Your Next SoC Project
Harness real-time performance and the rich features of Linux
Scott McNutt, Senior Software Engineer
58 l New-Tech Magazine Europe