const (
	D0	= PD0	// RX0
	D1	= PD1	// TX1
	D2	= PD2
	D3	= PD3
	D4	= PD4
	D5	= PD5
	D6	= PD6
	D7	= PD7
	D8	= PB0
	D9	= PB1
	D10	= PB2
	D11	= PB3
	D12	= PB4
	D13	= PB5

Digital pins.

const LED Pin = D13

LED on the Arduino

const (
	ADC0	Pin	= PC0
	ADC1	Pin	= PC1
	ADC2	Pin	= PC2
	ADC3	Pin	= PC3
	ADC4	Pin	= PC4	// Used by TWI for SDA
	ADC5	Pin	= PC5	// Used by TWI for SCL

ADC on the Arduino

const (

UART pins

const (
	PB0	= portB + 0
	PB1	= portB + 1	// peripherals: Timer1 channel A
	PB2	= portB + 2	// peripherals: Timer1 channel B
	PB3	= portB + 3	// peripherals: Timer2 channel A
	PB4	= portB + 4
	PB5	= portB + 5
	PB6	= portB + 6
	PB7	= portB + 7
	PC0	= portC + 0
	PC1	= portC + 1
	PC2	= portC + 2
	PC3	= portC + 3
	PC4	= portC + 4
	PC5	= portC + 5
	PC6	= portC + 6
	PC7	= portC + 7
	PD0	= portD + 0
	PD1	= portD + 1
	PD2	= portD + 2
	PD3	= portD + 3	// peripherals: Timer2 channel B
	PD4	= portD + 4
	PD5	= portD + 5	// peripherals: Timer0 channel B
	PD6	= portD + 6	// peripherals: Timer0 channel A
	PD7	= portD + 7
const (
	TWI_FREQ_100KHZ	= 100000
	TWI_FREQ_400KHZ	= 400000

TWI_FREQ is the I2C bus speed. Normally either 100 kHz, or 400 kHz for high-speed bus.

Deprecated: use 100 * machine.KHz or 400 * machine.KHz instead.

const (
	// I2CReceive indicates target has received a message from the controller.
	I2CReceive	I2CTargetEvent	= iota

	// I2CRequest indicates the controller is expecting a message from the target.

	// I2CFinish indicates the controller has ended the transaction.
	// I2C controllers can chain multiple receive/request messages without
	// relinquishing the bus by doing 'restarts'.  I2CFinish indicates the
	// bus has been relinquished by an I2C 'stop'.
const (
	// I2CModeController represents an I2C peripheral in controller mode.
	I2CModeController	I2CMode	= iota

	// I2CModeTarget represents an I2C peripheral in target mode.
const Device = deviceName

Device is the running program’s chip name, such as “ATSAMD51J19A” or “nrf52840”. It is not the same as the CPU name.

The constant is some hardcoded default value if the program does not target a particular chip but instead runs in WebAssembly for example.

const (
	KHz	= 1000
	MHz	= 1000_000
	GHz	= 1000_000_000

Generic constants.

const NoPin = Pin(0xff)

NoPin explicitly indicates “not a pin”. Use this pin if you want to leave one of the pins in a peripheral unconfigured (if supported by the hardware).

const (
	PinRising	PinChange	= 1 << iota
	PinToggle	= PinRising | PinFalling
const (
	PinInput	PinMode	= iota
const (
	Mode0	= 0
	Mode1	= 1
	Mode2	= 2
	Mode3	= 3

SPI phase and polarity configs CPOL and CPHA

const (
	// ParityNone means to not use any parity checking. This is
	// the most common setting.
	ParityNone	UARTParity	= iota

	// ParityEven means to expect that the total number of 1 bits sent
	// should be an even number.

	// ParityOdd means to expect that the total number of 1 bits sent
	// should be an odd number.


var (
	ErrTimeoutRNG		= errors.New("machine: RNG Timeout")
	ErrClockRNG		= errors.New("machine: RNG Clock Error")
	ErrSeedRNG		= errors.New("machine: RNG Seed Error")
	ErrInvalidInputPin	= errors.New("machine: invalid input pin")
	ErrInvalidOutputPin	= errors.New("machine: invalid output pin")
	ErrInvalidClockPin	= errors.New("machine: invalid clock pin")
	ErrInvalidDataPin	= errors.New("machine: invalid data pin")
	ErrNoPinChangeChannel	= errors.New("machine: no channel available for pin interrupt")
var DefaultUART = UART0

Always use UART0 as the serial output.

var (
	// UART0 is the hardware serial port on the AVR.
	UART0	= &_UART0
		Buffer:	NewRingBuffer(),

		dataReg:	avr.UDR0,
		baudRegH:	avr.UBRR0H,
		baudRegL:	avr.UBRR0L,
		statusRegA:	avr.UCSR0A,
		statusRegB:	avr.UCSR0B,
		statusRegC:	avr.UCSR0C,


var (
	Timer0	= PWM{0}	// 8 bit timer for PD5 and PD6
	Timer1	= PWM{1}	// 16 bit timer for PB1 and PB2
	Timer2	= PWM{2}	// 8 bit timer for PB3 and PD3
var I2C0 = &I2C{
	srReg:	avr.TWSR,
	brReg:	avr.TWBR,
	crReg:	avr.TWCR,
	drReg:	avr.TWDR,
	srPS0:	avr.TWSR_TWPS0,
	srPS1:	avr.TWSR_TWPS1,
	crEN:	avr.TWCR_TWEN,
	crEA:	avr.TWCR_TWEA,

I2C0 is the only I2C interface on most AVRs.

var SPI0 = SPI{
	spcr:	avr.SPCR,
	spdr:	avr.SPDR,
	spsr:	avr.SPSR,

	spcrR0:		avr.SPCR_SPR0,
	spcrR1:		avr.SPCR_SPR1,
	spcrCPHA:	avr.SPCR_CPHA,
	spcrCPOL:	avr.SPCR_CPOL,
	spcrDORD:	avr.SPCR_DORD,
	spcrSPE:	avr.SPCR_SPE,
	spcrMSTR:	avr.SPCR_MSTR,

	spsrI2X:	avr.SPSR_SPI2X,
	spsrSPIF:	avr.SPSR_SPIF,

	sck:	PB5,
	sdo:	PB3,
	sdi:	PB4,
	cs:	PB2,

SPI configuration

var (
	ErrPWMPeriodTooLong = errors.New("pwm: period too long")
var Serial = DefaultUART

Serial is implemented via the default (usually the first) UART on the chip.

var (
	ErrTxInvalidSliceSize		= errors.New("SPI write and read slices must be same size")
	errSPIInvalidMachineConfig	= errors.New("SPI port was not configured properly by the machine")

func CPUFrequency

func CPUFrequency() uint32

Return the current CPU frequency in hertz.

func InitADC

func InitADC()

InitADC initializes the registers needed for ADC.

func InitSerial

func InitSerial()

func NewRingBuffer

func NewRingBuffer() *RingBuffer

NewRingBuffer returns a new ring buffer.

type ADC

type ADC struct {
	Pin Pin

func (ADC) Configure

func (a ADC) Configure(ADCConfig)

Configure configures a ADCPin to be able to be used to read data.

func (ADC) Get

func (a ADC) Get() uint16

Get returns the current value of a ADC pin, in the range 0..0xffff. The AVR has an ADC of 10 bits precision so the lower 6 bits will be zero.

type ADCConfig

type ADCConfig struct {
	Reference	uint32	// analog reference voltage (AREF) in millivolts
	Resolution	uint32	// number of bits for a single conversion (e.g., 8, 10, 12)
	Samples		uint32	// number of samples for a single conversion (e.g., 4, 8, 16, 32)
	SampleTime	uint32	// sample time, in microseconds (µs)

ADCConfig holds ADC configuration parameters. If left unspecified, the zero value of each parameter will use the peripheral’s default settings.

type I2C

type I2C struct {
	srReg	*volatile.Register8
	brReg	*volatile.Register8
	crReg	*volatile.Register8
	drReg	*volatile.Register8

	srPS0	byte
	srPS1	byte
	crEN	byte
	crINT	byte
	crSTO	byte
	crEA	byte
	crSTA	byte

I2C on AVR.

func (*I2C) Configure

func (i2c *I2C) Configure(config I2CConfig) error

Configure is intended to setup the I2C interface.

func (*I2C) ReadRegister

func (i2c *I2C) ReadRegister(address uint8, register uint8, data []byte) error

ReadRegister transmits the register, restarts the connection as a read operation, and reads the response.

Many I2C-compatible devices are organized in terms of registers. This method is a shortcut to easily read such registers. Also, it only works for devices with 7-bit addresses, which is the vast majority.

func (*I2C) SetBaudRate

func (i2c *I2C) SetBaudRate(br uint32) error

SetBaudRate sets the communication speed for I2C.

func (*I2C) Tx

func (i2c *I2C) Tx(addr uint16, w, r []byte) error

Tx does a single I2C transaction at the specified address. It clocks out the given address, writes the bytes in w, reads back len(r) bytes and stores them in r, and generates a stop condition on the bus.

func (*I2C) WriteRegister

func (i2c *I2C) WriteRegister(address uint8, register uint8, data []byte) error

WriteRegister transmits first the register and then the data to the peripheral device.

Many I2C-compatible devices are organized in terms of registers. This method is a shortcut to easily write to such registers. Also, it only works for devices with 7-bit addresses, which is the vast majority.

type I2CConfig

type I2CConfig struct {
	Frequency uint32

I2CConfig is used to store config info for I2C.

type I2CMode

type I2CMode int

I2CMode determines if an I2C peripheral is in Controller or Target mode.

type I2CTargetEvent

type I2CTargetEvent uint8

I2CTargetEvent reflects events on the I2C bus

type NullSerial

type NullSerial struct {

NullSerial is a serial version of /dev/null (or null router): it drops everything that is written to it.

func (NullSerial) Buffered

func (ns NullSerial) Buffered() int

Buffered returns how many bytes are buffered in the UART. It always returns 0 as there are no bytes to read.

func (NullSerial) Configure

func (ns NullSerial) Configure(config UARTConfig) error

Configure does nothing: the null serial has no configuration.

func (NullSerial) ReadByte

func (ns NullSerial) ReadByte() (byte, error)

ReadByte always returns an error because there aren’t any bytes to read.

func (NullSerial) Write

func (ns NullSerial) Write(p []byte) (n int, err error)

Write is a no-op: none of the data is being written and it will not return an error.

func (NullSerial) WriteByte

func (ns NullSerial) WriteByte(b byte) error

WriteByte is a no-op: the null serial doesn’t write bytes.

type PDMConfig

type PDMConfig struct {
	Stereo	bool
	DIN	Pin
	CLK	Pin

type PWM

type PWM struct {
	num uint8

PWM is one PWM peripheral, which consists of a counter and two output channels (that can be connected to two fixed pins). You can set the frequency using SetPeriod, but only for all the channels in this PWM peripheral at once.

func (PWM) Channel

func (pwm PWM) Channel(pin Pin) (uint8, error)

Channel returns a PWM channel for the given pin.

func (PWM) Configure

func (pwm PWM) Configure(config PWMConfig) error

Configure enables and configures this PWM.

For the two 8 bit timers, there is only a limited number of periods available, namely the CPU frequency divided by 256 and again divided by 1, 8, 64, 256, or 1024. For a MCU running at 16MHz, this would be a period of 16µs, 128µs, 1024µs, 4096µs, or 16384µs.

func (PWM) Counter

func (pwm PWM) Counter() uint32

Counter returns the current counter value of the timer in this PWM peripheral. It may be useful for debugging.

func (PWM) Period

func (pwm PWM) Period() uint64

Period returns the used PWM period in nanoseconds. It might deviate slightly from the configured period due to rounding.

func (PWM) Set

func (pwm PWM) Set(channel uint8, value uint32)

Set updates the channel value. This is used to control the channel duty cycle, in other words the fraction of time the channel output is high (or low when inverted). For example, to set it to a 25% duty cycle, use:

pwm.Set(channel, pwm.Top() / 4)

pwm.Set(channel, 0) will set the output to low and pwm.Set(channel, pwm.Top()) will set the output to high, assuming the output isn’t inverted.

func (PWM) SetInverting

func (pwm PWM) SetInverting(channel uint8, inverting bool)

SetInverting sets whether to invert the output of this channel. Without inverting, a 25% duty cycle would mean the output is high for 25% of the time and low for the rest. Inverting flips the output as if a NOT gate was placed at the output, meaning that the output would be 25% low and 75% high with a duty cycle of 25%.

Note: the invert state may not be applied on the AVR until the next call to ch.Set().

func (PWM) SetPeriod

func (pwm PWM) SetPeriod(period uint64) error

SetPeriod updates the period of this PWM peripheral. To set a particular frequency, use the following formula:

period = 1e9 / frequency

If you use a period of 0, a period that works well for LEDs will be picked.

SetPeriod will not change the prescaler, but also won’t change the current value in any of the channels. This means that you may need to update the value for the particular channel.

Note that you cannot pick any arbitrary period after the PWM peripheral has been configured. If you want to switch between frequencies, pick the lowest frequency (longest period) once when calling Configure and adjust the frequency here as needed.

func (PWM) Top

func (pwm PWM) Top() uint32

Top returns the current counter top, for use in duty cycle calculation. It will only change with a call to Configure or SetPeriod, otherwise it is constant.

The value returned here is hardware dependent. In general, it’s best to treat it as an opaque value that can be divided by some number and passed to Set (see Set documentation for more information).

type PWMConfig

type PWMConfig struct {
	// PWM period in nanosecond. Leaving this zero will pick a reasonable period
	// value for use with LEDs.
	// If you want to configure a frequency instead of a period, you can use the
	// following formula to calculate a period from a frequency:
	//     period = 1e9 / frequency
	Period uint64

PWMConfig allows setting some configuration while configuring a PWM peripheral. A zero PWMConfig is ready to use for simple applications such as dimming LEDs.

type Pin

type Pin uint8

Pin is a single pin on a chip, which may be connected to other hardware devices. It can either be used directly as GPIO pin or it can be used in other peripherals like ADC, I2C, etc.

func (Pin) Configure

func (p Pin) Configure(config PinConfig)

Configure sets the pin to input or output.

func (Pin) Get

func (p Pin) Get() bool

Get returns the current value of a GPIO pin when the pin is configured as an input or as an output.

func (Pin) High

func (p Pin) High()

High sets this GPIO pin to high, assuming it has been configured as an output pin. It is hardware dependent (and often undefined) what happens if you set a pin to high that is not configured as an output pin.

func (Pin) Low

func (p Pin) Low()

Low sets this GPIO pin to low, assuming it has been configured as an output pin. It is hardware dependent (and often undefined) what happens if you set a pin to low that is not configured as an output pin.

func (Pin) PortMaskClear

func (p Pin) PortMaskClear() (*volatile.Register8, uint8)

Return the register and mask to disable a given port. This can be used to implement bit-banged drivers.

Warning: there are no separate pin set/clear registers on the AVR. The returned mask is only valid as long as no other pin in the same port has been changed.

func (Pin) PortMaskSet

func (p Pin) PortMaskSet() (*volatile.Register8, uint8)

Return the register and mask to enable a given GPIO pin. This can be used to implement bit-banged drivers.

Warning: there are no separate pin set/clear registers on the AVR. The returned mask is only valid as long as no other pin in the same port has been changed.

func (Pin) Set

func (p Pin) Set(value bool)

Set changes the value of the GPIO pin. The pin must be configured as output.

func (Pin) SetInterrupt

func (pin Pin) SetInterrupt(pinChange PinChange, callback func(Pin)) (err error)

type PinChange

type PinChange uint8

Pin Change Interrupts

type PinConfig

type PinConfig struct {
	Mode PinMode

type PinMode

type PinMode uint8

PinMode sets the direction and pull mode of the pin. For example, PinOutput sets the pin as an output and PinInputPullup sets the pin as an input with a pull-up.

type RingBuffer

type RingBuffer struct {
	rxbuffer	[bufferSize]volatile.Register8
	head		volatile.Register8
	tail		volatile.Register8

RingBuffer is ring buffer implementation inspired by post at

func (*RingBuffer) Clear

func (rb *RingBuffer) Clear()

Clear resets the head and tail pointer to zero.

func (*RingBuffer) Get

func (rb *RingBuffer) Get() (byte, bool)

Get returns a byte from the buffer. If the buffer is empty, the method will return a false as the second value.

func (*RingBuffer) Put

func (rb *RingBuffer) Put(val byte) bool

Put stores a byte in the buffer. If the buffer is already full, the method will return false.

func (*RingBuffer) Used

func (rb *RingBuffer) Used() uint8

Used returns how many bytes in buffer have been used.

type SPI

type SPI struct {
	// The registers for the SPIx port set by the chip
	spcr	*volatile.Register8
	spdr	*volatile.Register8
	spsr	*volatile.Register8

	spcrR0		byte
	spcrR1		byte
	spcrCPHA	byte
	spcrCPOL	byte
	spcrDORD	byte
	spcrSPE		byte
	spcrMSTR	byte

	spsrI2X		byte
	spsrSPIF	byte

	// The io pins for the SPIx port set by the chip
	sck	Pin
	sdi	Pin
	sdo	Pin
	cs	Pin

SPI is for the Serial Peripheral Interface Data is taken from page 169 and following

func (SPI) Configure

func (s SPI) Configure(config SPIConfig) error

Configure is intended to setup the SPI interface.

func (SPI) Transfer

func (s SPI) Transfer(b byte) (byte, error)

Transfer writes the byte into the register and returns the read content

func (SPI) Tx

func (spi SPI) Tx(w, r []byte) error

Tx handles read/write operation for SPI interface. Since SPI is a syncronous write/read interface, there must always be the same number of bytes written as bytes read. The Tx method knows about this, and offers a few different ways of calling it.

This form sends the bytes in tx buffer, putting the resulting bytes read into the rx buffer. Note that the tx and rx buffers must be the same size:

spi.Tx(tx, rx)

This form sends the tx buffer, ignoring the result. Useful for sending “commands” that return zeros until all the bytes in the command packet have been received:

spi.Tx(tx, nil)

This form sends zeros, putting the result into the rx buffer. Good for reading a “result packet”:

spi.Tx(nil, rx)

type SPIConfig

type SPIConfig struct {
	Frequency	uint32
	LSBFirst	bool
	Mode		uint8

SPIConfig is used to store config info for SPI.

type UART

type UART struct {
	Buffer	*RingBuffer

	dataReg		*volatile.Register8
	baudRegH	*volatile.Register8
	baudRegL	*volatile.Register8

	statusRegA	*volatile.Register8
	statusRegB	*volatile.Register8
	statusRegC	*volatile.Register8

UART on the AVR.

func (*UART) Buffered

func (uart *UART) Buffered() int

Buffered returns the number of bytes currently stored in the RX buffer.

func (*UART) Configure

func (uart *UART) Configure(config UARTConfig)

Configure the UART on the AVR. Defaults to 9600 baud on Arduino.

func (*UART) Read

func (uart *UART) Read(data []byte) (n int, err error)

Read from the RX buffer.

func (*UART) ReadByte

func (uart *UART) ReadByte() (byte, error)

ReadByte reads a single byte from the RX buffer. If there is no data in the buffer, returns an error.

func (*UART) Receive

func (uart *UART) Receive(data byte)

Receive handles adding data to the UART’s data buffer. Usually called by the IRQ handler for a machine.

func (*UART) Write

func (uart *UART) Write(data []byte) (n int, err error)

Write data over the UART’s Tx. This function blocks until the data is finished being sent.

func (*UART) WriteByte

func (uart *UART) WriteByte(c byte) error

WriteByte writes a byte of data over the UART’s Tx. This function blocks until the data is finished being sent.

type UARTConfig

type UARTConfig struct {
	BaudRate	uint32
	TX		Pin
	RX		Pin
	RTS		Pin
	CTS		Pin

UARTConfig is a struct with which a UART (or similar object) can be configured. The baud rate is usually respected, but TX and RX may be ignored depending on the chip and the type of object.

type UARTParity

type UARTParity uint8

UARTParity is the parity setting to be used for UART communication.

Last modified April 17, 2024: Fix doc-gen and update docs (8a74a2b)