Introduction
Raspberry Pi has gained significant attention due to its low-cost single-board computers for teaching and learning environments desktop systems and others. However, there is a possibility that few people are aware of the fact that Raspberry Pi is heavily involved in silicon designing and it has its own ASIC team. On this note, this commentary shall give general information about Raspberry Pi’s ASIC design team as postulated in the article. It will comprise the experiences of the team’s design process, issues faced, and the successes achieved within a decade.
What is an ASIC team?
ASIC on the other hand is a microchip, which has been specifically designed for a specific application, and not for general use. These custom silicon chips are designed and developed by an ASIC team to serve the specific application of the device. There operates the Raspberry Pi ASIC team which was founded approximately 10 years ago to develop purpose-built ASICs for usage in the Raspberry Pi lineup of products.
The team is led by Tammy Julyan ASIC Engineering Director and Nick Francis ASIC Technical Director. They have a staff of skilled silicon engineers and work collaboratively with other teams at Raspberry Pi such as software, hardware, and management. Their role is to take ideas for new chips from initial specifications all the way through the complex design, testing, and manufacturing process to produce finished silicon.
Why does Raspberry Pi need an ASIC team?
While early Raspberry Pi boards used off-the-shelf chips, having an in-house ASIC design capability allows Raspberry Pi more flexibility and control over their hardware. Integrated circuits designed specifically for Raspberry Pi’s needs can be optimized for performance, power usage, cost, and integration into product designs.
Some examples of chips designed by the ASIC team include the RP2040 microcontroller used in the Raspberry Pi Pico and the RP1 I/O controller for the Raspberry Pi 5. These contain blocks of IP (intellectual property), which are units of circuit designs that can be reused, obtained from other sources, or designed in-house. Having an ASIC team enables Raspberry Pi to integrate specialized functions tailored to its products rather than relying entirely on commercial chips.
The design process
The article provides insight into the multi-step process the ASIC team undertakes to design each new integrated circuit. Here are the key stages:
- Specification – Gathering requirements from various sources like new product ideas, customers, and marketing. For RP1, the goal was an I/O controller chip for Raspberry Pi 5.
- Architecture – An iterative process where the whole team discusses the “shape and feel” of the design considering many factors like performance, interfaces, and software support.
- Design – Constructing the chip architecture using blocks of IP that may already exist or need to be designed. Describing the design in Verilog, a hardware description language analogous to C.
- Verification – Extensive testing through simulation and FPGAs to ensure the design functions as expected before manufacturing. This takes most of the design time.
- Physical Implementation – Synthesizing the Verilog into a physical layout, placing and routing components, adding test structures, and optimizing for timing and power constraints.
- Manufacturing – Sending the design files to a wafer foundry that grows silicon wafers, applying photolithography to etch the chip patterns, and cutting the wafers into individual dies.
Verification is key
Verification is arguably one of the most significant and elaborate stages that form a design solution with most of the time consumed. Silicon, on the other hand, cannot have the correction applied at a later date, as with many forms of software, which means that silicon designs have to be rigorously tested before production. The ASIC team uses a variety of techniques:
- Simulation tools to stimulate the design with software and check outputs
- Constrained random testing to find hard-to-predict corner cases
- FPGAs for near-real-time hardware testing prior to silicon availability
- Integrating with software teams for system-level validation
Verification takes the bulk of the design time because even well-tested software can more easily be changed, while flawed silicon requires a new design iteration. Getting the design right the first time through extensive simulation and emulation is critical.
Physical design considerations
After the design is functionally verified in Verilog, it must be implemented physically on the silicon die. This involves tasks like floorplanning, placement, and routing:
- Floorplanning positions memory blocks, analog components, and I/O around the die dimensions
- Synthesis converts Verilog into standard cell gates based on timing models
- Placement inserts the standard cells optimally in rows for timing closure
- Routing connects all the placed cells with metal interconnects
- Power and clock distribution meshes are added
- Testing structures are incorporated for the production of DFT
- Timing constraints are met through iterative optimization
The physical design translates the logical functionality into a manufacturable layout that efficiently implements the circuit at the transistor level within area, power, and speed constraints.
Manufacturing silicon chips
Once the chip designs have been developed, the chip is then given for construction by a semiconductor foundry manufacturer. Some key wafer processing steps include:
- Growing cylindrical silicon crystals and slicing wafers
- Applying and patterning photosensitive photoresist through photolithography
- Etching geometric shapes using the photoresist masks to define transistors
- Ion implantation to dope silicon with n-type or p-type impurities
- Thermal oxidation to grow silicon dioxide gates
- Depositing and patterning metal layers to form interconnects
- Cutting and packaging individual dies into encapsulated chips
- Electrical testing to weed out defective chips
While relying on foundry manufacturing allows Raspberry Pi to leverage billions in capital spent on facilities, getting designs manufactured successfully requires considering process variations and characterization.
Ongoing evolution of the ASIC team
Over the past decade, Raspberry Pi has built a multidisciplinary ASIC team from the ground up with expertise spanning electrical engineering, computer science, and chip design. They have gained valuable experience through projects like RP2040, RP1, and future undisclosed designs. Some key achievements and learnings include:
- Developing in-house EDA tool flows and best practices for design reuse
- Choosing and integrating IP blocks from external vendors
- Optimizing for advanced process technologies at partner foundries
- Streamlining simulation methodologies to efficiently validate designs
- Driving embedded software development in tandem with chip development
- Expanding multiphysics simulation capabilities (power, thermal, etc.)
As the team matures, their capabilities continue to advance, enabling more ambitious chips tailored for Raspberry Pi’s evolving portfolio of innovative computing platforms and products. They will play an important role in the company’s future technological innovations.
Conclusion
This commentary has provided an overview of Raspberry Pi’s dedicated ASIC design team, the complex chip design process they undertake, and their accomplishments over the past decade. While relatively new to chip design, they have built substantial expertise through hands-on experience delivering customized silicon like RP2040 and RP1. The ASIC team exemplifies Raspberry Pi’s pioneering spirit in open hardware innovation and will no doubt spearhead many more breakthrough integrated circuit technologies. Their work reducing barriers to silicon design will inspire future engineers for years to come.
FAQ
Q: Why did Raspberry Pi start an ASIC design team?
A: Having an in-house chip design capability allows Raspberry Pi more control over customizing silicon optimized for their products. It provides flexibility beyond using off-the-shelf chips and enables the integration of specialized functions.
Q: How long has the ASIC team been operating?
A: The ASIC design team was established around 10 years ago in 2012. They have been steadily growing their expertise and experience through multiple chip projects since then.
Q: What chips have they designed?
A: Two of their most prominent chips are the RP2040 microcontroller used in the Raspberry Pi Pico and the RP1 I/O controller for the Raspberry Pi 5 computer. They are also likely working on future undisclosed chips.
Q: How big is the ASIC team?
A: The article mentions it is led by an Engineering Director and Technical Director but does not provide an exact team size. As a small but growing part of Raspberry Pi, it likely consists of several dozen skilled silicon engineers.
Q: Can anyone design chips?
A: Chip design is complex and intricate work that entails numerous years of practice in subjects for example electrical engineering, computer science, and exclusive chip software. Although enthusiasm is renowned it takes experience and time to hone the aforementioned silicon design expertise.
