STM32 Journal - Digikey

STM32 Journal
Bringing 32-bit Performance
to 8- and 16-bit Applications
By Reinhard Keil, Director of MCU Tools, ARM Germany GmbH
Shawn Prestridge, Senior Field Applications Engineer, IAR Systems
Sean Newton, Field Applications Engineering Manager, STMicroelectronics
Today’s embedded applications
are being called upon to
provide an increasing number
of capabilities. More and more
devices need to be connected,
require greater precision, must
offer a graphics-based interface
with touch capabilities, utilize
sophisticated signal processing,
and support multimedia playback.
In the past, developers were
compelled by cost constraints
to base their designs on 8- and
16-bit architectures that limited
performance. Now, with the
availability of next-generation
MCUs like the STM32 F0 that
provide 32-bit performance
at 8-bit budget pricing, OEMs
can bring substantial value to
end-users without having to
compromise functionality. In
addition, powerful development
tools like Keil’s MDK-ARM and
IAR Embedded Workbench
enable developers new to 32-
bit programming to immediately
exploit the full capabilities of the
STM32 F0 architecture.
The 32-bit Advantage
There are several ways in which
the STM32 F0 lowers product
cost compared to 8- and 16-bitbased
designs. Specifically,
because these MCUs tend to be
based on legacy architectures,
they have many limitations that
slow development by forcing
designers to work around the
architecture, so to speak. For
example, to complete a 16 x 16
multiplication for a processing
algorithm, a 16-bit CPU requires
four multiplies and several
additions, depending upon the
implementation. An 8-bit CPU
would require significantly more
cycles. With the STM32 F0, this
takes a single instruction.
The result is code that makes
better utilization of MCU
resources, leading to faster
operation, more performance per
MHz, higher code density, and
greater power efficiency. Since
each instruction does more per
clock cycle, applications can be
written using less code. In addition
to accelerating development,
shorter code is easier to debug as
well. Together, all of these benefits
lead to lower system cost.
Cost, however, is only one of
the numerous advantages the
STM32 F0 has over 8- and 16-
bit architectures. The STM32
F0 is a full embedded MCU
built using the same STM32
DNA that the rest of the STM32
family has, including excellent
real-time performance, DMA,
high-resolution ADC and DAC
peripherals, motor control
timers, and connectivity
interfaces. These integrated
capabilities bring tremendous
efficiency to cost-sensitive
designs in a way that limited
8- and 16-bit MCU architectures
cannot (see Figure 1).
For example, the availability of
a 32-bit bus not only speeds
data transfers and increases
computing performance, it
improves system reliability.
Consider the challenge of reading
a 12-bit DAC using an 8-bit bus
where the CPU has to read the
DAC twice to capture the entire
sample. If an interrupt occurs
between these reads, the DAC
data may be overwritten by the
next sample before the interrupt
is completed and the second
read can be executed. To prevent
this, developers have to manually
disable interrupts for every
such “atomic” operation in an
application. If even one instance
is missed, this creates a potential
for an intermittent error that will
be extremely difficult to resolve.
DMA: Moving Data
Efficiently
The STM32 F0 is a modern
architecture integrating the
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