Those were changes
already in progress, but the Internet of Things (IoT) appears to be
having a major influence on how microcontroller technology develops.
In
broad terms, the IoT comprises three elements: edge devices, which
often perform one dedicated function; hubs or fusion devices, which
integrate data from edge devices; and larger processing elements. It's
the first two categories which are currently focusing the minds of MCU
developers. The reason? The IoT demands two things above all others –
minimal power consumption and the lowest possible cost. Thomas Barber,
director of marketing for wireless products with Silicon Laboratories,
explained why. "Estimates suggest there may be 30billion edge devices.
They can't all consume 1W because we don't have enough energy, so they
need to consume microWatts and they need to be inexpensive."
Andreas
Eieland, Atmel's senior product marketing manager for flash MCUs,
agreed. "Being able to have the right features at the right power
consumption will be critical. Edge devices will need to run from
harvested energy or for their full lifetime from a single battery."
Geoff
Lees, general manager of Freescale's microcontroller business, added:
"We are being directed towards more and more integration. What were low
cost devices need to have more RAM, more resources, but we can't
increase the power budget or the price. That is pushing us to move
geometries such as 40nm and 28nm more quickly than we would have
expected."
While the three companies agree on the general shape
of the IoT market, where they differ is on the technology that will be
applied at the various layers. But all agree that MCUs targeted at the
IoT will need to offer wireless connectivity.
Silicon Labs, for
example, has just released the Si106x/108x range of wireless MCUs,
designed with the IoT in mind (see fig 1). And sitting at the heart of
these parts is an 8051 core; not the 32bit device you might expect.
There's also a sub GHz RF transceiver and peripherals such as a 10bit
A/D converter, comparators, 16bit timers and serial interfaces.
Barber
said: "Every time there's an 'obit' for the 8051, it keeps going and
we're not betting on it going away. There is a large base of developers
who like it and it will continue to sell." But Silicon Labs can also
offer devices based on the ARM architecture; not only its own designs,
but also from recently acquired Energy Micro. "ARM sees the Cortex-M0 as
an 8bit killer," Barber continued, "but it will come down to customer
preference."
Eieland noted that power requirements will drive
this element. "MCUs will have to consume less than 1µA and less than
200nA in deep sleep. Whatever 'wins' will have to offer 8bit type
performance.
"Atmel makes 8051 based MCUs, but if you want to
connect to ZigBee, for example, our AVR cores are a better choice."
Atmel's offerings here include devices from its ATMega range. "But we
also have a Cortex-M0+ part that competes in that sector."
Lees
noted: "You can make the 8051 work, but what happens when you have a lot
of sensor data which is more than 8bit? We see the Cortex-M0+ as a
major platform for edge node devices, but we're already seeing more
products with what would have been thought of as an excess of
processing."
For the moment, Freescale is targeting its Kinetis-L
range of M0+ based devices at edge devices, but Lees perceives that,
even at the edge, there will be the need for more performance. "Where
there would have had one processor, we're now seeing an M0+ as sensor
hub and a Cortex-M4 as the apps processor handling communications."
What
is also generally agreed is that the standalone microcontroller will
be, to some extent, superseded by an SoC implementation. Barber said:
"We'll see devices with lots of peripherals and memory and we won't have
one chip that meets all needs." And he believes that, in the long term,
integration on die will be preferable to in package integration. "It's
always better to integrate on die; it's cheaper and a better solution."
Lees
pointed out: "As fast as you can integrate, there are more sensors –
and some we've not heard of before. So these parts will have sensors,
low power connectivity and sufficient processing."
In terms of in
package integration, Atmel has worked with Bosch Sensortec on the
development of the BNO055, said to be one of the first application
specific sensor nodes to be announced. "There are six dice in the
package," Eieland noted, "including a SAM D20 MCU. It's a good example
of how we are working with sensor manufacturers to get the most size
efficient solutions possible."
While Lees is confident that MCUs
for IoT applications will need to be made on low geometry processes,
Barber and Eieland are not so sure. Eieland thinks refinement of
existing technology may be sufficient. "We don't think we want to go to
55nm because leakage at that node will be significant. Processes in the
range from 100nm to 150nm may well be suitable, with one more product
generation needed to evolve the low power aspects."
Barber
implied that smaller geometries may not be at the top of Silicon Labs'
agenda. "We will win the process technology battle," he asserted,
"assuming we've done the right things to control leakage. Architectures
will become more important, with more efficient computation. The longer
you can keep the MCU powered down, the better off you will be, so the
device will need to come in and out of sleep modes and to feature
autonomous peripherals which don't wake the core up.
"We're still
trying to maximise battery life and energy consumption is critical. How
you have low consumption for a device with a lot of functionality? But I
think another two device generations will get us to the price and power
points we need to hit."
Lees noted: "Freescale has already moved
Kinetis to 90nm and there will be a more rapid move to smaller
geometries. We are fighting leakage in deep sub micron, but we are
putting a lot of work into developing libraries, power gating and so on.
All of this work is now becoming a fundamental part of MCU design.
"The
power budget is a continuing discussion point in all my design teams;
it limits what we can do and directs our road map towards next
generation energy efficient cores."
And that road map could be
interesting. "Although Freescale is a lead partner with ARM for its
Cortex-M cores, we are beginning to see more IoT applications suited to
low end Cortex-A processors, rather than high end Cortex-M cores," Lees
concluded. "Application processors are coming to the domestic market,
and that's something that was unexpected."