Wearables is one key domain with lot of space and opportunity for innovative product designs ranging from fitness t rackers, health monitors, lifestyle support for elderly, personal trackers for kids etc all the way up to full blown smart watches. Considering the wide range of products within a single domain and each one of them exhibiting polar power and performance requirements It would be quite interesting to explore various choices that a system designer has to go through when it comes to micro-processor/micro controller selection.! In this write up, we will be exploring several fundamental factors and challenges affecting wearable product design and discuss how ARM® IP based silicon products address each one them in a basic way. ! Cost of development as a factor is not discussed deliberately as it might be highly subjective and beyond the scope of this writeup.

1. Wearable Product Design & ARM® Cortex® M Core !
Raahul Raghavan(raahul@glytonsolutions.com), Lead Systems Architect, Glyton Solutions !
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Wearables is one key domain with
lot of space and opportunity for
innovative product designs ranging
from fitness trackers, health
monitors, lifestyle support for
elderly, personal trackers for kids
etc all the way up to full blown
smart watches. Considering the
wide range of products within a
single domain and each one of
them exhibiting polar power and
performance requirements It would
be quite interesting to explore
various choices that a system
designer has to go through when it
comes to micro-processor/micro-
controller selection.!
In this write up, we will be exploring
several fundamental factors and
challenges affecting wearable
product design and discuss how
ARM® IP based silicon products
address each one them in a basic
way. !
Cost of development as a factor is
not discussed deliberately as it
might be highly subjective and
beyond the scope of this write up.!
!
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Key Challenges!
!
Following are few characteristic
challenges when it comes to
wearable products development
where processor selection might
have a direct impact!
!
• Energy Efficiency!
• Effective On-Chip peripheral
Interface!
• Time to Market & Development
ecosystem
!
1. Energy Efficiency!
!
A wearable product must be highly
energy efficient as typical usage
scenarios might pan across
several days between battery re-
charge cycle. !
Consider a wearable patient
monitor which reports a patients
v i t a l s i g n s i n c l u d i n g b o d y
temperature, heart rate etc. If there
is a need to get the product
removed from the patient to get the
battery recharged say for every 8
hours, might prove to be extremely
in-effective design rendering critical
care almost impossible. At the
time,in a wearable product , it might
not be mechanically feasible to
integrate a high capacity battery

2. which might eventually cater to
multi day operational requirement
without having the need to
recharge. !
In such cases the product design
must include a highly energy
efficient processor with a variety of
low power modes and battery smart
features which eventually delivers
extended battery life and at the
same time does not compromise
both accuracy and time bound
operations for the the life of the
product. Such an energy efficient
processor might also help in
efficient and cost effective battery
design which can get recharged to
full potential within relatively shorter
duration thereby reducing the
i n d i r e c t c o s t o f p h y s i c a l l y
monitoring the vital signs of a
patient.!
There are several ARM® IP
powered products which enable a
host of battery smart and energy
efficient features leveraging ARM ®
Cortex® M architecture without
compromising attributes like
multiple peripheral support, multiple
interrupt support, low active power
consumption etc. !
WFI (Wake from Interrupt), WFE
(Wake from Event) etc are few
samples to several different
a r c h i t e c t u r a l l y d e fi n e d
characteristics in ARM® IP based
silicon products.!
!
2. Effective On-Chip Peripheral
Interface!
!
Mechanical design of any wearable
product would be quite challenging
as several different functionalities
might need to be packed within
incredibly compact form factors.
Consider the same wearable
patient monitor discussed above, it
might pack several bio-sensors
ranging from pulse oximeters, heart
rate and temperature sensors. The
sensor array which packs all the
required sensors might need to be
packed and interfaced to the
processor in such a way that the
complete product comes out as a
really wearable one so that the
patient feels comfortable. !
More over the sensor array will
have couple of limitations when it
comes to contact patch with the
patients skin. In most cases, the
accuracy of readings reported back
might be directly affected by any
variation when it comes to sensor
array placement. So, the processor
in a wearable product such as this
might need to support several
peripherals with different interface
capabilities including I2C, I2S and
SPI on chip without the need to
h a v e s e p a r a t e i n t e r f a c e
controllers,pin expanders and glue
logic on board. !
Every other on board expansion for
peripheral support as opposed to

3. on chip logic will pose significant
challenges during mechanical
design phase.!
ARM® IP based products offer
several options when it comes to
interfacing peripherals. Most of the
silicon products based on ARM®
Cortex® M come with a variety of
on-chip solutions including I2C, SPI
etc and most of them are highly
optimized for performance through
s p e c i a l i z e d b u s i n t e r f a c e s
architecturally defined by ARM® !
!
3. T i m e t o M a r k e t &
Development Ecosystem!
!
Following board design, firmware /
software development is another
key milestone which might have
either significant positive or
negative impact when it comes to
time to market. During this phase
the innate on-chip debugging
capabilities of the processor might
be a key consideration. !
Given the variety of tasks a
wearable product such as patient
monitors might have to support, the
d e v e l o p e r m i g h t b e f u l l y
empowered to implement and test
the required algorithms only if the
processor implements highly
effective debug channels ranging
from comparators, watch points to
performance monitoring units and
dedicated channels which can be
used to debug as well as collect
trace data on various run time
performance attributes.!
ARM® and several silicon partners,
provide a host of both hardware
and software debugging solutions
ranging from DS-5 to several
customized tools from individual
silicon vendors. These tools
typically pack various functionalities
in a single IDE so that the
developer will have easy access to
all the debug capabilities exposed
by the ARM® Cortex® processor.
F P B ( F l a s h P a t c h a n d
Breakpoint),DWT (Data Watchpoint
& Trace), TPIU / Serial Wire
interface, ETM & ITM interface etc
are the several different ARM®
Coresight debug functionalities
which are architecturally defined by
ARM® and implemented by several
silicon vendors.!
!
Further Reading!
!
As indicated, this write up just
touches upon few challenges
involved across various phases in
wearable products development.
For further information related,
please do refer to either ARM®
architecture specific documentation
or technical reference manuals
provided by the specific silicon
vendor.!
ARM® , Cortex® M are registered
trademarks of ARM Holdings Plc!
!

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