December 2017: The Future of Microprocessors

Welcome to the December 2017 edition of the Embedded Artistry Newsletter!

This month I'd like to share my research on interesting innovations and research projects that will affect the future of microcontroller design and manufacturing.

The Future of Microprocessor Development and Manufacturing

In the past few months I've written to you about Intel's new FinFET transistor and "hyperscaling" chip design techniques and new DARPA electronic initiatives. I want to share my research on other innovations and programs that will affect microprocessor design and manufacturing.

Bespoke Processors

Most processors designed today are "general purpose" and meant to support a wide range of applications. By relying on general purpose processors, the manufacturing ecosystem can take advantage of economies of scale and enjoy reduced component costs. Even in situations where generic processors are too powerful for our specific application, it's cheaper to purchase an overpowered processor than it is to design an application-specific one.

Over-design is still costly, as unused features still have an impact on product size and power consumption. A research team at the University of Minnesota is investigating methods for identifying unused peripherals and logic gates in these generic processors. The team found that many of their test applications (e.g. FFT, autocorrelation, interpolation filtering) only used about 60% of the logic gates. They then created "bespoke" application-specific processors that removed completely unused circuitry. The resulting chip designs were on average 62% smaller and 50% lower-power than the starting openMSP430 microcontroller design. Since this effort is still early in its development, the solution is not yet cost-effective or manufacturable. However, it does allude to a future where we can create small, low-power, application-specific processors.

More on bespoke processors:

Embedded FPGAs

Field Programmable Gate Array (FPGA) technology allows for designers to describe a hardware/chip design using a programming language such as Verilog or VHDL. Traditionally FPGAs have been expensive, standalone components that are part of a hardware design. However, chip designers are increasingly making use of "embedded FPGAs" (eFPGA) in new microcontroller designs. In fact, you may already be using a chip with eFPGA technology without realizing it!

An embedded FPGA is an IP block that allows an FPGA to be integrated into a microcontroller design. Unlike standalone FPGA chips, eFPGAs rely on normal digital interconnects instead of supporting PHYs and I/O interfaces. eFPGA IP blocks provide the same benefits as standalone FPGAs (such as reprogrammability), but their tight coupling inside of the processor can result in higher communication speed and lower power consumption.

Embedded FPGAs provide a variety of chip design benefits:

  • Reduced impact of design changes - instead of expensive RTL changes, software can be updated
  • Reprogrammable and configurable I/O - allowing a single design to support a variety of I/O combinations (GPIO, UART, USART, I2C, I2S, SPI, etc.)
  • Offloading I/O processing from the MCU
  • Dramatically improved hardware accelerator performance (e.g. AES, SHA, FFT, JPEG encoding)
  • Creating reconfigurable hardware accelerators or implementing multiple accelerators using one mask
  • Maximizing battery life by implementing repetitive DSP/processor operations in a more efficient manner

While designers are primarily using eFPGAs to improve flexibility and reduce the impact of RTL changes, I look forward to a time when we will be able to program eFPGAs directly to maximize performance in our applications.

More on eFPGAs:

Embedded DARPA Initiatives

We covered two new DARPA efforts in October: 3DSoC, which is focused on creating design strategies for 3D circuit layouts; and FRANC, which seeks to overturn the Von Neumann architecture and create a new method for handling memory and logic operations. The other new DARPA initiatives are focused on improving the SoC design process to create a new era of innovation in electronics and application-specific designs:

  • Intelligent Design of Electronic Assets (IDEA) is focused on creating a design framework to enable non-experts to quickly design new complex electronics, including mixed-signal ICs, system-in-package modules, and PCBs
  • Posh Open Source Hardware (POSH) is focused on creating an open-source hardware design and verification framework to simplify SoC development
  • Software Defined Hardware (SDH) is exploring technology to create and improve reconfigurable software and hardware systems for use in data-intensive real-time processing applications, such as autonomous driving
  • Domain-Specific System on a Chip (DDSoC) is focused on creating a single platform to create and program SoCs for application-specific needs

More on the new DARPA initiatives:

Plastic Processors

Researchers at ARM and PragmatIC have been working on PlasticARM, a project focused on creating cheap, disposable micro-controllers printed on plastic. PlasticARM is based on the ARM Cortex-M0 32-bit SoC and currently uses a 2 micron process. The ARM team is also working with the University of Minnesota team to use the bespoke processor technique to reduce size and complexity of the resulting chips.

While not bleeding edge computationally, plastic chips will benefit from an estimated 90% lower IC cost than silicon chips. Plastic chips can also be flexible, thinner than a human hair, and have no rigid interconnection points. This could lead to interesting use cases, such as:

  • Disposable packaging displays
  • Sensors around water pipes to record average water pressure
  • Sensors around gas pipes to detect leaks
  • Sensors telling you whether your food is rancid or not
  • Pill bottle displays telling you whether you forgot to take your pills

More on plastic processors:

Lithographic Printing

Silicon chips are currently produced using the complex photolithographic printing process. Photoresist material is applied to a silicon wafer and spun at high speeds to produce a uniform layer. The photoresist is cured using UV light, and some of the photoresist is removed by a special solution. Afterward, a chemical etching process removes the uppermost substrate layer wherever the wafer is not protected by photoresist. This process is repeated to produce patterned layers of various materials that eventually result in a wafer of functional chips.

Molecular Imprints is a company working on utilizing imprint lithography (IL) to stamp out chips using a process similar to a printing press. Photoresist is applied to the silicon wafer using a method similar to inkjet printing. Then a glass stamp with the etching pattern is lowered onto the wafer, and the stamp draws the photoresist into its grooves via capillary action. Since the stamp is glass, the resist can be cured with UV light while the stamp is still on the wafer.

While there are still quality control problems to solve, the IL process is much simpler than photolithographic printing: simply spray photoresist, check alignment, stamp the wafer, and repeat. While Molecular Imprints is initially targeting hard drive production, I expect we will see printed processors soon enough.

More on Imprint Lithography:

Around the Web

Phil Koopman, of Better Embedded Software has made the course notes for his new embedded software college course publicly available. The course covers code quality, safety, and security. You can also find the course materials on the CMU course website.

Want to get started with ARM assembly? Check out this excellent 7-part series by Azeria Labs covering ARM assembly basics. took a look at how embedded software development has evolved. Using surveys collected over the past twenty years, they explore evolutions in programming languages, processor usage, OS usage, and more.

Popular Articles

These were the most popular Embedded Artistry articles in November:

  1. Circular Buffers in C/C++
  2. Installing LLVM/Clang on OSX
  3. Implementing Malloc: First-fit Free List
  4. An Overview of C++ STL Containers
  5. std::string vs C-strings
  6. A GitHub Pull Request Template for Your Projects
  7. Creating and Enforcing a Code Formatting Standard with clang-format
  8. clang-format Wrapper Script Examples
  9. Implementing an Asynchronous Dispatch Queue
  10. A GitHub Issue Template for Your Projects

Thanks for Reading!

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Happy hacking!