AikaPi

AikaPi is a C++ library for bare-metal access to Raspberry Pi peripherals. It provides direct register-level control of GPIO, SPI, DMA, PWM, system timers, interrupts, and clock management, all through a clean object-oriented interface.

Features

GPIO

• Pin function selection (input, output, alt functions 0-5)
• Pull-up/pull-down configuration
• Read/write individual pins
• Event detection (rising/falling edge, high/low level, async)

SPI

• Hardware SPI (SPI0) with configurable clock frequency
• Auxiliary SPI (SPI1 and SPI2) via the AUX peripheral
• Bit-banged SPI (SPI_BB) for arbitrary GPIO pins, supporting all four SPI modes
• Configurable bit order (MSB/LSB first), chip select polarity, and clock polarity

DMA

• 16-channel DMA controller access
• Control block management
• Start, stop, pause, and abort transfers
• Interrupt handling and status queries
• Peripheral DREQ mapping for paced transfers

PWM

• Two-channel PWM output
• Balanced and mark-space algorithms
• Configurable frequency and duty cycle
• FIFO mode support

Clock Manager

• PWM and PCM clock control
• Configurable clock source (oscillator, PLLA, PLLC, PLLD, HDMI)
• MASH noise-shaping divisor modes
• Frequency setting with automatic divisor calculation

System Timer

• Access to the free-running 64-bit microsecond counter

Interrupts

• IRQ and FIQ register access

Uncached Memory

• VideoCore mailbox-based memory allocation
• Bus/physical/virtual address translation
• Used for DMA control blocks and buffers

Supported Boards

AikaPi auto-detects the board revision at runtime and maps the correct peripheral base address:

Processor	Boards	Peripheral Base
BCM2835	Pi 1, Pi Zero, Pi Zero W	0x20000000
BCM2836	Pi 2	0x3F000000
BCM2837	Pi 3, Pi Zero 2W	0x3F000000
BCM2711	Pi 4, Pi 400, CM4	0xFE000000

Architecture

AikaPi is implemented as a lazy singleton. All peripherals are accessed through the single AikaPi instance:

AikaPi& rpi = AikaPi::get_instance();

// GPIO
rpi.gpio.set(pin, AP::GPIO::FUNC::OUTPUT, AP::GPIO::PULL::OFF);
rpi.gpio.write(pin, true);

// Hardware SPI
rpi.spi.frequency(1'000'000.0);

// Auxiliary SPI
rpi.aux.spi(0).frequency(500'000.0);
rpi.aux.spi(0).xfer(rx_buf, tx_buf, length);

// DMA
rpi.dma.start(channel, cb_bus_addr);

// PWM
rpi.pwm.frequency(0, 1000.0);
rpi.pwm.duty_cycle(0, 50.0);
rpi.pwm.start(0);

// System timer
uint32_t time_us = rpi.st.low();

Internal Structure

AikaPi (singleton)
├── gpio           - GPIO register access
├── spi            - Hardware SPI (SPI0)
├── aux            - Auxiliary peripherals
│   └── spi(0/1)   - Auxiliary SPI (SPI1/SPI2)
├── dma            - DMA controller (16 channels)
├── pwm            - PWM controller (2 channels)
├── cm             - Clock manager
│   ├── pwm        - PWM clock
│   └── pcm        - PCM clock
├── st             - System timer
└── interrupt      - Interrupt controller

Files

AikaPi.h    - Header with all class definitions, register offsets, and constants
AikaPi.cpp  - Implementation

Usage

AikaPi is a header-only dependency. Add both AikaPi.h and AikaPi.cpp to your project and compile them alongside your source files.

add_executable(my_project
  main.cpp
  path/to/AikaPi.cpp
)

The library requires access to /dev/mem and /dev/vcio, so the program must be run with root privileges:

sudo ./my_project

Reference

• BCM2835 ARM Peripherals Datasheet
• BCM2835 Datasheet Errata
• Raspberry Pi Peripheral Addresses
• VideoCore Mailbox Property Interface
• BCM2835 Audio Clocks

Disclaimer

This project is for research and educational purposes only. It is not intended for production use.

License

MIT License. See LICENSE for details.