OneBus

HAPI bus protocol components — SPI, I2C/TWI, UART, 1-Wire, and I2C GPIO expander. Parameterized on chip from OneChip; zero dynamic allocation, pure-static dispatch.

Part of the InternetOfPins project family.

SPI

#include <oneBus/spiMaster.h>
using namespace oneBus;

// AVR hardware SPI — clock = F_CPU / speed_divisor
using MySpi = SpiMaster<SPI_CLOCK_DIV4>;
MySpi::begin();
MySpi::select();             // assert CS (your OutPin)
uint8_t b = MySpi::transfer(0xFF);
MySpi::deselect();

For ESP32: Esp32SpiMaster<> in OneChip, which also provides transfer(buf, len).

I2C / TWI

#include <oneBus/twiMaster.h>

// AVR hardware TWI — 100 kHz at 16 MHz
using MyI2c = hw::avr::AvrTwiMaster<100000UL, F_CPU>;
MyI2c::begin();
MyI2c::begin_write(0x3C);
MyI2c::write_byte(0x00);
MyI2c::write_byte(data);
MyI2c::end_write();

UART

#include <oneBus/uart.h>

Chip-family Serial aliases live in OneBus/uart.h. Chip definitions (baud rates, register addresses) come from OneChip.

1-Wire

Two cores are provided:

OneWire<PinN> — Arduino bit-bang (any target)

#include <oneBus/oneWire.h>

using Bus = oneBus::OneWire<4>;  // Arduino pin 4
Bus::begin();
bool present = Bus::reset();
Bus::skip();                      // 0xCC — address single device
Bus::writeByte(0x44);             // Convert T (DS18B20)

AvrOneWire<Port, Bit> — direct register, cycle-accurate (AVR only)

#include <oneBus/oneWire.h>
#include <chips/avr/avrPort.h>

// PC4 = Arduino A4 on ATmega328P
using Bus = oneBus::AvrOneWire<hw::avr::chip::PortC, 4>;

AvrOneWire uses direct DDR/PORT/PIN register access and _delay_us() (cycle-counted at F_CPU). cli()/sei() guard only the critical edges of each bit slot; the 480 µs reset pulse runs with interrupts enabled.

Both cores expose the same protocol API: begin(), reset(), writeByte(), readByte(), skip().

I2C GPIO expander — PCF8574

#include <oneBus/i2cGpio.h>

// InitShadow = 0x08 → bit 3 high (backlight on for LCD backpacks)
using Port = oneBus::I2cGpio<MyI2c, 0x27, 0x08>;
using RS   = typename Port::Pin<0>;
using EN   = typename Port::Pin<2>;

Port::begin();
RS::on();
EN::off();

I2cGpio<> manages a shadow register for read-modify-write; pin changes are batched into a single I2C write per flush() (or immediately if you prefer).

Dependencies

• HAPI
• OneChip

License

MIT — see LICENSE.

Author: Rui Azevedo (neu-rah) · Azores, Portugal