The OnChip Open-V microcontroller is a completely free (as in freedom) and open source 32-bit microcontroller based on the RISC-V architecture. The Open-V has a host of built-in peripherals you’d expect of any modern microcontroller and was designed to compete with the capabilities of ARM M0-based microcontrollers. This crowdfunding campaign will bring the Open-V into mass production and make it widely available to anyone. If you love hacking on embedded controllers, breaking down closed-source barriers, having the freedom to learn how things work even down to the transistor level, or have dreamed of spinning your own silicon, then this campaign is for you and we need your help!

First Mass-produced RISC-V Chip

The Reduced Instruction Set Computing (RISC) paradigm has been around for decades and many processors fall into this category. RISC-V (pronounced "risk-five") is a particular implementation of RISC concepts as an open source instruction set architecture (ISA). Although the RISC-V standard has been around (and evolved) since 2010, it has never been used in a chip available on the open market. Some chips have been manufactured using RISC-V, but they have been relegated to the research lab and academia. We’re going to change that. With the OnChip Open-V, for the first time ever, you will be able to purchase a RISC-V-based chip and use it in real projects and products. This isn’t just a one-time thing - we’re planning on keeping the Open-V in production for as long as there is demand. Our initial manufacturing run will produce approximately 70,000 chips.

An Open-V bare die

Free and Open Source Silicon

We’ve open sourced all files for the entire OnChip Open-V design, including the register-transfer level (RTL) files for the CPU and all peripherals and the development and testing tools we use. These sources are available under the MIT license from our GitHub account.

We think open source integrated circuit (IC) design will give the semiconductor industry the reboot it needs to get out of the deep innovation rut dug by the entrenched players. Just like open source software ushered in the last two decades of software innovation, open source silicon will unleash a flood of hardware innovation. The Open-V microcontroller is one concrete step in that direction.

With open silicon, you can:

• completely understand how your hardware works
• build customized ICs without reinventing the wheel
• optimize performance by tuning parameters usually hidden
• teach a new generation of engineers with a real-world example
• debug and even correct errors in a chip without waiting for the vendor
• reduce costs by cutting out licensing fees

A bare Open-V die wire bonded to our OSH Park test board

Chips & Development Boards

In this campaign, you can order the Open-V chips themselves and a development board we’ve designed around the Open-V chip.

Open-V Chip Specifications

• Package
  • QFN-32
  • No other packages are planned for the first run
• Processor
  • RISC-V ISA version 2.1
  • 1.2 V operation
• Memory
  • 8 KB SRAM
• Clock
  • 32 KHz - 160 MHz
  • Two PLLs, user-tunable with muxers and frequency dividers
  • Includes all clocking and bias circuitry
• True Random Number Generator
  • 400 KiB/s
  • See announcement for details
• Analog Signals
  • Two 10-bit ADC channels, each running at up to 10 MS/s
  • Two 12-bit DAC channels
• Timers
  • One general-purpose 16-bit timer
  • One 16-bit watch dog timer (WDT)
• General Purpose Input/Ouput
  • 16 programmable GPIO pins
  • Two external interrupts
• Interfaces
  • SDIO port (e.g., microSD)
  • Two SPI ports
  • I2C
  • UART
• Programming and Testing
  • Built-in debug module for use with gdb and JTAG
  • Programmable PRBS-31/15/7 generator and checker for interconnect testing
  • Compatible with the Arduino IDE

Open-V Dev Board Specifications

The dev board comes completely assembled.

• USB 2.0 controller
• 1.2 V and 3.3 V voltage regulators
• Clock reference
• Breadboard-compatible breakout header pins
• microSD receptacle
• Micro USB connector (power and data)
• JTAG connector
• 32 KB EEPROM
• 32-pin QFN Open-V microcontroller
• Dimensions: 55 mm x 30 mm (excluding USB receptacle)

Render of the Open-V dev board

Arduino Compatibility

The Open-V core is Arduino-compatible, which means you will benefit from the abundant resources of the Arduino community. As we make progress toward manufacturing the first batch of Open-V chips, we will release demos showing how Open-V can be used with the Arduino toolchain and other resources.

Of course, the Open-V chip can be used completely independently from the Arduino ecosystem. For example, the RISC-V ecosystem is rapidly growing and immediately applicable for Open-V development.

RISC-V

Many commercial microcontrollers feature proprietary, licensed instruction sets. Licensed instruction sets and microprocessor cores restrict the process of modifying the core for different purposes such as improving performance and adapting it to specific applications.

RISC-V is a new open instruction set architecture (ISA) designed by the Berkeley Architecture Group with the aim to support architecture research and education. RISC-V is fully available to public and has advantages such as a smaller footprint size, support for highly-parallel multi-core implementations, variable-length instructions to support an optional dense instruction, ease of implementation in hardware, and energy efficiency.

Moreover, because Open-V and RISC-V are open, a curious person will be able to read and modify the register-transfer level (RTL) and propose changes to enhance the performance of Open-V. A maker would be able to understand the architecture by testing the RTL core with FPGAs or simulators. Already, researchers made some interesting RISC-V-based chips unrelated to Open-V.

Peripherals

The OnChip Open-V is the first microcontroller featuring both an open source CPU and open source peripherals. The glue between the CPU and peripherals (i.e., the buses), is also open source, both the specification and the actual implementation. Currently, we have ADC, DAC, SPI, I2C, UART, GPIO, PWM, and timer peripherals designed and tested in real silicon. We are working on other peripherals, such as USB 2, USB3, internal NVRAM and/or EEPROM, and a convolutional neural network (CNN).

The Importance of Buses

The Open-V microcontroller uses several portions of the Advanced Microcontroller Bus Architecture (AMBA) open standard for on-chip interconnection. This makes any Open-V functional block, such as the core or any of the peripherals, easy to incorporate into existing chip designs that also use AMBA. We hope this will motivate other silicon companies to release RISC-V-based microcontrollers using the peripherals they’ve already developed and tested with ARM-based cores.

We think buses are so important, we even wrote a paper about them for IEEE LASCAS 2016.

Chip Comparison

Power and area simulations show that a RISC-V architecture like that used in the Open-V can be used to replace ARM M0+ microcontrollers with similar performance. The table below shows some comparable chipsets and how they stack up.

* Dynamic power measurement condition for Open-V: three while loops executed from SRAM, all peripheral clocks disabled, VDD = 1.2 V, Temperature = 25° C

Non-volatile Memory

Notably absent from the Open-V specifications is an internal non-volatile memory. The dev board will ship with an external 32 KB EEPROM, but the Open-V chip itself currently does not have an internal non-volatile memory. We are working to change that and hope to include non-volatile memory in the first batch of Open-V chips, but there are challenges yet to overcome.

Integration of non-volatile memory on regular CMOS technology is a challenge since the intellectual property is controlled by only a few companies and literature is lacking. Similarly, an IP license for NVRAM for pure CMOS has been difficult to find. Just a few companies control this market, their licensing offices are not friendly, and they haven’t yet responded to us as we would hope.

EEPROM will require additional masks and will increase the cost of the mask set, as well as increase the wafer cost. We have designed our own NVRAM, to be really open, and we are aiming to test it in the MPW in March 2017 (see schedule below). We are doing a design effort to get our NVRAM design to accommodate at least a bootloader capable of getting data from an external EEPROM and/or SD Card.

Our wire bonding machine at work

Changing the Semiconductor Industry

We have over 30 years of cumulative experience designing chips in the semiconductor industry and we believe the industry can do better. We aim to open the door to chip design to a larger community and in so doing drive down the cost of innovation.

The semiconductor industry is today where the operating system and compiler industry was several decades ago: knowledge is concentrated in a small number of specialists using highly inefficient tools whose configuration and parameter tweaking alone take up the vast majority of the time and effort expended. We need to move away from a world in which a team with US- and India-based engineers cost upward of $100,000 per day.

The problem is simple: the people supposedly solving problems in the semiconductor industry are not themselves users of their own solutions. For example, rarely does a chip designer know the end application of the chip they are designing or the company who commissioned the chip in the first place. Similarly, the creators of electronic design automation (EDA) tools (the software used to design new chips) aren’t in the business of designing chips.

The solution is equally simple: spread the knowledge of chip design to those people who actually need a new chip to solve a real problem. The best way to do this is by open sourcing everything from the ground up. This will spur innovation and force existing players to be more competitive.

The OnChip Open-V is a concrete step in this direction. With the Open-V, for the first time, open silicon will be widely available. We hope it will be used in ways we haven’t yet imagined.

An Open-V bare die in a tray

Manufacturing Plan

The microcontroller will be manufactured by Taiwan Semiconductor Manufacturing Company (TSMC), who has a lot of experience manufacturing integrated circuits with state-of-the-art features. The development boards will be made and assembled separately.

2017

• 03/31 MPW Design Review
• 04/24 MPW with v2 prototype tapeout
• 06/17 PCBs for v2 fabricated
• 07/18 Bare dies received
• 08/25 MPW dies completely tested
• 09/13 PCB for packaged chip tested
• 10/26 Production level final design review
• 11/22 Production level tapeout

2018

• 01/19 Wafer level testing/sorting
• 02/23 Package level testing/sorting
• 03/22 PCBs populated and tested
• 04/27 Delivery

Our testing board with a wire-bonded Open-V bare die

Risks & Challenges

An analog and digital integrated circuit design is a complex venture, involving architecture design, circuit design, verification, software design, and more. As with any major engineering project, the Open-V carries the risks associated with such complexity. Although rigorous debugging and testing has been and will continue to be exercised throughout this project, there exists the possibility of bugs creeping in. Commercial chips often have bugs, but usually their bugs have a work around that can impact performance but not be a complete showstopper. However, a single unfixable bug is enough to make a chip unusable.

We are confident we can minimize the impact of potential bugs in the following three ways:

1. Our well-defined design flow and functional project management.
2. Our 30+ years of aggregate experience taping out integrated chips.
3. Our enthusiasm for solving high-level challenges.

While the third parties associated with the project are trustworthy and have a track record of good work, it’s also clear their activities constitute a risk not in our control. Of course, we will keep everyone updated at each milesone and we will be transparent about any problems that might arise.