The RP1 is an in-house designed silicon I/O controller developed by the Raspberry Pi team specifically for the Raspberry Pi 5. This intricate piece of hardware combines both analogue interfaces and digital controllers, bringing together features such as MIPI camera input, USB support, analogue video output, Gigabit Ethernet MAC, and numerous general-purpose I/O pins. All these components are housed within a single 20mm² die, marking a significant milestone in Raspberry Pi's engineering endeavours, as it showcases their capability to produce their own tailored silicon components.

In this blog post we're going to explore different features of the RP1.

MCU

• Dual-arm Cortex-M3 microcontroller
• 64KB SRAM
• Tightly-Coupled Memory (TCM)
• BootROM for platform configuration and management

The MCU (MicroController Unit) within the RP1 boasts a dual-arm Cortex-M3 design, which provides it with dual-core processing capabilities, facilitating potentially parallel tasks or improved multitasking. Accompanying this is 64KB of SRAM, a type of rapid memory essential for the temporary storage and quick retrieval of data. Additionally, the MCU employs Tightly-Coupled Memory (TCM), a feature that offers faster data access times by virtue of its close integration with the microcontroller – an asset for real-time processing needs.

Furthermore, the presence of a BootROM for platform configuration and management ensures a reliable startup and initialisation process. Compared to other MCUs, the inclusion of dual-core architecture, combined with the benefits of TCM and an efficient BootROM, might provide the RP1's MCU with a performance edge or specific tailored functionalities. However, the true distinction would be based on the application context and how these features are utilised in conjunction with the broader RP1 system.

Host Interface

• PCIe 2.0 x4 bus

The Host Interface within the RP1 employs a PCIe 2.0 x4 bus. PCIe, which stands for Peripheral Component Interconnect Express, is a high-speed interface standard used for connecting add-on cards, like graphics cards, to a computer's motherboard. The "2.0" indicates the version of the PCIe standard, with each iteration generally bringing about enhancements in speed and efficiency. The "x4" specifies that the bus has four lanes, meaning there are four parallel data pathways allowing for data transmission. In practical terms, this ensures a faster data transfer rate compared to a bus with fewer lanes, like x1 or x2. When compared to other host interfaces, the PCIe 2.0 x4 in the RP1 offers a balanced performance level, suitable for a wide range of applications, though it might not be as fast as more recent PCIe standards with more lanes, such as PCIe 3.0 x16. Nevertheless, the chosen interface likely aligns well with the intended use and design goals of the RP1.

MIPI Camera/Display Interfaces

• 2x MIPI CSI-2 camera controllers and 2x MIPI DSI display controllers
• Connected to 2x shared 4-lane MIPI DPHY transceiver PHYs for up to 8 Gbps bandwidth.
• Each camera controller incorporates an image signal processor front-end (ISP-FE) which pre-processes incoming image data.
• Possible configurations: 2x cameras, 2x displays, or one display + one camera

The RP1 is equipped with advanced MIPI Camera/Display Interfaces, designed to cater to multimedia needs. It boasts 2x MIPI CSI-2 camera controllers and 2x MIPI DSI display controllers. MIPI CSI-2 (Camera Serial Interface) and MIPI DSI (Display Serial Interface) are standards specifically for connecting cameras and displays, respectively, to processors in devices like smartphones and tablets. These controllers are paired with 2x shared 4-lane MIPI DPHY transceiver PHYs, facilitating an impressive bandwidth of up to 8 Gbps. This configuration ensures high-speed data transmission, vital for high-definition imagery and video. Notably, each camera controller is embedded with an image signal processor front-end (ISP-FE). This ISP-FE is responsible for the initial processing of incoming image data, refining image quality before further processing. The RP1 offers versatile configurations, allowing for combinations of 2x cameras, 2x displays, or a mix of one display plus one camera. Compared to other platforms, the RP1's MIPI interfaces underline its commitment to high-quality multimedia processing, supported by robust bandwidth and integrated preprocessing capabilities.

Networking

• Gigabit Ethernet MAC (RGMII)

The RP1 encompasses advanced networking capabilities through its inclusion of a Gigabit Ethernet MAC (Media Access Control) that operates via the RGMII (Reduced Gigabit Media Independent Interface) standard. Gigabit Ethernet refers to a networking standard that can handle data transmission speeds up to 1 gigabit per second (1 Gbps), which is considerably faster than older Ethernet standards. The RGMII interface is a streamlined method for connecting the MAC layer to the Ethernet PHY (physical layer), optimised for gigabit speeds while reducing the number of required pins. This ensures efficient and rapid data transfer, making it suitable for applications demanding high bandwidth. When juxtaposed with other networking interfaces, the Gigabit Ethernet MAC with RGMII in the RP1 signifies its aptitude for handling robust data traffic, aligning with contemporary networking demands and offering high-speed Ethernet connectivity.

USB

• 2x XHCI controllers each connected to a single USB 3.0 PHY and a single USB 2.0 PHY
• Up to 10 Gbps total bandwidth (5Gbps per XHCI controller)

The RP1 exhibits proficient USB capabilities through its integration of 2x XHCI controllers, each connected to both a single USB 3.0 PHY (Physical Layer) and a single USB 2.0 PHY. XHCI stands for eXtensible Host Controller Interface, which is a standard for USB host controller hardware. The presence of USB 3.0 PHY indicates that the RP1 supports USB 3.0 speeds, which can achieve data transfer rates of up to 5 Gbps. With two XHCI controllers, this culminates in a combined bandwidth of up to 10 Gbps. Additionally, the inclusion of USB 2.0 PHYs ensures backward compatibility with older USB devices. Compared to systems with only USB 2.0 support, the RP1's USB infrastructure underscores its ability to handle high-speed data transfers while maintaining versatility for a broad spectrum of USB devices. This arrangement ideally positions the RP1 to cater to modern connectivity demands without compromising on compatibility with legacy devices.

GPIOs

• 28x GPIO pins
  • 5V tolerant
  • 3.3V-failsafe (supports a voltage of up to 3.63V applied when RP1 is unpowered)
• GPIO alternate functions

The RP1 features a robust set of General-Purpose Input/Output (GPIO) capabilities with its inclusion of 28 GPIO pins. These pins are versatile and have been designed to be resilient in varied operating conditions. Notably, they are 5V tolerant, meaning they can safely handle input voltages up to 5V, catering to a wide array of interfacing peripherals. Furthermore, they possess a 3.3V-failsafe feature, which ensures that the pins can tolerate a voltage of up to 3.63V even when the RP1 itself is unpowered. This fail-safe mechanism provides added protection against potential damage or data corruption during power fluctuations or inadvertent power applications.

Additionally, the mention of "GPIO alternate functions" implies that these pins are multifunctional. This means that, aside from their primary role as general input or output channels, they can be configured to serve specialized purposes, such as UART, SPI, or I2C communication, depending on the system's requirements. Compared to more basic GPIO configurations, the RP1's GPIO infrastructure showcases its adaptability and resilience, ensuring both flexibility in application and robustness in operation.

Storage

• eMMC/SDIO bus with a 4-bit interface

The RP1 is equipped with a storage interface that supports eMMC/SDIO bus connectivity, specifically using a 4-bit interface. eMMC, which stands for embedded MultiMediaCard, is a type of flash storage commonly found in smartphones, tablets, and other embedded devices. It offers reliable performance and integrated flash memory management. On the other hand, SDIO (Secure Digital Input Output) is a standard that allows devices to interface with Secure Digital (SD) cards, often used for additional storage or specific peripheral functions. The mention of a 4-bit interface means that data can be transferred over four parallel lines, enabling faster data communication compared to a simpler 1-bit interface. When looking at storage capabilities in various devices, the RP1's support for both eMMC and SDIO with a 4-bit interface indicates its ability to interface with dependable embedded storage solutions and a variety of SD-based devices, all while ensuring decent transfer speeds and versatility in storage options.

Display

• 24-bit DPI output

The RP1 incorporates a display feature with a 24-bit DPI (Display Parallel Interface) output. The 24-bit specification denotes that the display can represent up to 16.7 million colours, offering full RGB colour depth with 8 bits for each of the red, green, and blue channels. Such depth ensures that images and graphics are rendered with high colour accuracy, resulting in vibrant and lifelike visuals. DPI is a parallel interface, meaning multiple data lines are used to transmit information simultaneously, which can offer a robust and speedy connection between the RP1 and attached display modules. Compared to displays with lesser colour depths, the RP1's 24-bit DPI output emphasises its capability to deliver superior visual quality, making it well-suited for applications that demand rich and detailed visual content.

Audio

• 2x I2S
• Stereo PWM audio output (AUDIO_OUT)

The RP1 boasts a sound audio configuration, featuring 2x I2S interfaces and a Stereo PWM audio output labelled as AUDIO_OUT. I2S, or Inter-IC Sound, is a standard used for transmitting digital audio between devices. Having 2x I2S suggests the RP1 can manage multiple digital audio streams concurrently, making it suitable for applications with complex audio requirements. On the other hand, the Stereo PWM (Pulse Width Modulation) audio output facilitates the generation of analogue audio signals. Using PWM for audio involves varying the duty cycle of a digital signal to create an analogue waveform, producing sound when connected to a speaker or audio device. The stereo designation implies that the RP1 can deliver audio on two channels, typically left and right, providing a fuller, more immersive sound experience. When compared to devices with only basic audio capabilities, the RP1's audio features highlight its potential to handle both digital and analogue audio formats, catering to a diverse range of audio needs and ensuring a high-quality sound output.

Additional Interfaces

• 5x UART
• 6x SPI
• 4x I2C
• 4-channel PWM output
• Interrupt generation from pin level or edge transitions

The RP1 comes packed with a variety of additional interfaces to ensure versatility in its applications.

• It features 5x UART (Universal Asynchronous Receiver-Transmitter) interfaces, which are fundamental for asynchronous serial communication between devices, frequently used in debugging and interfacing with various peripherals.

• With 6x SPI (Serial Peripheral Interface) channels, the RP1 can communicate with multiple devices simultaneously using a master-slave configuration, ideal for fast data transfers between the main processor and peripheral devices like SD cards or sensors.

• The 4x I2C (Inter-Integrated Circuit) interfaces allow for bidirectional communication between integrated circuits over short distances, commonly utilised for connecting sensors, displays, and other modules.

• A 4-channel PWM (Pulse Width Modulation) output is present, which can be employed for a range of applications, from controlling motor speed to adjusting the brightness of LEDs.

• Furthermore, the RP1 has the capability for interrupt generation based on pin level or edge transitions. This feature enables the device to respond promptly to specific changes in input, such as a button press or a sensor triggering, without constantly polling the state of the input, leading to efficient and responsive operations.

When juxtaposed with platforms having limited interface capabilities, the RP1 stands out due to its extensive array of communication interfaces, underlining its adaptability to connect with a diverse range of peripherals and handle a variety of tasks simultaneously.

Clocks

• 1x Clock Producer instance
• 1x Clock Consumer instance
• General-purpose clock input and output (GPCLK)

The RP1 incorporates a specific arrangement of clocks to manage the timing and synchronisation of its operations.

• It features a "Clock Producer instance," which is likely responsible for generating the primary clock signals. These clock signals drive the timing of operations and data transfers within the RP1, ensuring that tasks are executed in sync and data is communicated reliably.

• Complementing the producer, there's a "Clock Consumer instance." This component probably takes the clock signals produced by the Clock Producer and utilises them for specific modules or peripherals, ensuring that they operate in harmony with the main system.

• Additionally, the RP1 offers a General-purpose clock input and output, referred to as GPCLK. This feature provides flexibility as it allows the RP1 to receive external clock signals (input) or transmit its internal clock signals to other devices (output). Such capability can be crucial when interfacing with peripherals that require precise timing or synchronising multiple devices to a common clock source.

When compared to systems with a more rudimentary clock setup, the RP1's clock architecture indicates a sophisticated approach to timing and synchronisation, ensuring optimal performance and seamless interactions with various connected devices.

RIO

• Registered IO interface to allow the host processor to manipulate GPIOs

The RP1 incorporates an RIO feature, which stands for Registered IO. This interface is specially designed to empower the host processor with the ability to directly manipulate GPIOs (General-Purpose Input/Output pins).

In essence, the RIO interface acts as a bridge between the main processing unit and the GPIO pins. By employing a "registered" system, each interaction or change on the GPIOs is logged or registered, enabling more controlled and potentially faster GPIO operations. This setup provides a systematic approach to handle GPIO manipulations, allowing for precise control, monitoring, and potentially more efficient interactions with peripherals or other connected devices.

Compared to systems that might directly access GPIOs without such an interface, the RP1's RIO feature underscores a more structured and potentially more reliable way of handling GPIO operations, ensuring that the host processor can swiftly and accurately interact with these pins as needed.

Misc

• 8-channel DMA Controller (DMAC) for servicing low-speed peripherals.
• 3x integrated PLLs
  • 2 fractional-N PLLs for independent video and audio clocks
  • 1x integer PLL for system clocks
• A five-input successive-approximation analog-to-digital (ADC) converter
  • 12-bit resolution at 500kSPS
  • 9.5 ENOB (Effective number of bits)
  • 4 external inputs
  • One internal temperature sensor

The RP1 incorporates several miscellaneous features to support its multifaceted operations:

• 8-channel DMA Controller (DMAC): This controller is responsible for direct memory access, which allows certain hardware subsystems within the device to access system memory for reading and writing. The RP1's DMAC is particularly designed to service low-speed peripherals, ensuring efficient data transfers without involving the central processor for each transaction, thus optimising performance.

• 3x integrated PLLs (Phase-Locked Loops): PLLs are used in electronics to generate a stable frequency output from a variable input. In the context of the RP1:

  • 2 fractional-N PLLs are dedicated to managing independent video and audio clocks. This ensures that both audio and video operations are synchronised and executed without jitter or lag.
  • 1 integer PLL is assigned for system clocks, ensuring the overall stability and synchronisation of the system's operations.

• Analog-to-digital (ADC) converter: This is an essential component that converts analog signals, like those from sensors or other external sources, into digital data that the processor can understand.

  • It offers a 12-bit resolution, allowing for precise readings, at a speed of 500kSPS (kilo-samples per second).
  • With a 9.5 ENOB (Effective Number of Bits), the ADC ensures that the converted digital data is of high fidelity, closely representing the original analog signal.
  • The ADC supports 4 external inputs, which means it can simultaneously or sequentially read from four different sources.
  • Additionally, it includes an internal temperature sensor, which might be used for monitoring the chip's temperature, ensuring safe and efficient operations.

Compared to simpler configurations, the RP1's miscellaneous features showcase its comprehensive design. The inclusion of such diverse components suggests a platform built for performance, flexibility, and precision, ensuring it can efficiently handle a wide range of tasks and interfaces.

Dimensions

• 20mm² die

The RP1 is characterized by its compactness, featuring a 20mm² die for its dimensions. The term "die" in semiconductor manufacturing refers to a block or piece of semiconductor material from which the integrated circuits are constructed. The given measurement indicates the physical area the RP1 occupies on the silicon wafer. At 20mm², the RP1 signifies a condensed and efficient design, aiming to fit a significant number of transistors and components within this space. Such a compact dimension often points to advanced semiconductor manufacturing processes and design methodologies. When compared to larger dies, the RP1's dimension might suggest a balance between performance and size, potentially resulting in reduced power consumption and increased efficiency while ensuring the device's capabilities aren't compromised.

Process

• TSMC’s 40LP (Note: the BCM2712 is manufactured with a 16nm process)

The RP1 is manufactured using TSMC’s 40LP process. TSMC, or Taiwan Semiconductor Manufacturing Company, is a renowned semiconductor foundry that produces chips for various electronics companies. The "40LP" denotes a 40-nanometre Low Power process, indicating the size of the transistors and the technology's focus on energy efficiency. A smaller nanometre number usually signifies a more advanced process with denser and more efficient transistors, leading to improved performance and reduced power consumption.

For context, the main system on a chip (the BCM2712), is manufactured with a 16nm process. This means that the BCM2712 uses even smaller, 16-nanometre transistors, making it a more advanced and denser semiconductor process compared to the 40LP used for the RP1.

In comparison, while the 40LP process of the RP1 is more mature and potentially less expensive to produce, the 16nm process of the BCM2712 suggests higher performance and efficiency, albeit possibly at a higher production cost. The choice of process technology is often a balance between performance, power consumption, and cost, tailored to the intended application and design goals of the chip.