tinygo/src/machine/machine_atmega.go

// +build avr,atmega

package machine

import (
	"device/avr"
	"runtime/interrupt"
	"runtime/volatile"
	"unsafe"
)

// I2C on AVR.
type I2C struct {
}

// I2C0 is the only I2C interface on most AVRs.
var I2C0 *I2C = nil

// I2CConfig is used to store config info for I2C.
type I2CConfig struct {
	Frequency uint32
}

// Configure is intended to setup the I2C interface.
func (i2c *I2C) Configure(config I2CConfig) error {
	// Default I2C bus speed is 100 kHz.
	if config.Frequency == 0 {
		config.Frequency = TWI_FREQ_100KHZ
	}

	// Activate internal pullups for twi.
	avr.PORTC.SetBits((avr.DIDR0_ADC4D | avr.DIDR0_ADC5D))

	// Initialize twi prescaler and bit rate.
	avr.TWSR.SetBits((avr.TWSR_TWPS0 | avr.TWSR_TWPS1))

	// twi bit rate formula from atmega128 manual pg. 204:
	// SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
	// NOTE: TWBR should be 10 or higher for controller mode.
	// It is 72 for a 16mhz board with 100kHz TWI
	avr.TWBR.Set(uint8(((CPUFrequency() / config.Frequency) - 16) / 2))

	// Enable twi module.
	avr.TWCR.Set(avr.TWCR_TWEN)

	return nil
}

// 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 *I2C) Tx(addr uint16, w, r []byte) error {
	if len(w) != 0 {
		i2c.start(uint8(addr), true) // start transmission for writing
		for _, b := range w {
			i2c.writeByte(b)
		}
	}
	if len(r) != 0 {
		i2c.start(uint8(addr), false) // re-start transmission for reading
		for i := range r {            // read each char
			r[i] = i2c.readByte()
		}
	}
	if len(w) != 0 || len(r) != 0 {
		// Stop the transmission after it has been started.
		i2c.stop()
	}
	return nil
}

// start starts an I2C communication session.
func (i2c *I2C) start(address uint8, write bool) {
	// Clear TWI interrupt flag, put start condition on SDA, and enable TWI.
	avr.TWCR.Set((avr.TWCR_TWINT | avr.TWCR_TWSTA | avr.TWCR_TWEN))

	// Wait till start condition is transmitted.
	for !avr.TWCR.HasBits(avr.TWCR_TWINT) {
	}

	// Write 7-bit shifted peripheral address.
	address <<= 1
	if !write {
		address |= 1 // set read flag
	}
	i2c.writeByte(address)
}

// stop ends an I2C communication session.
func (i2c *I2C) stop() {
	// Send stop condition.
	avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWSTO)

	// Wait for stop condition to be executed on bus.
	for !avr.TWCR.HasBits(avr.TWCR_TWSTO) {
	}
}

// writeByte writes a single byte to the I2C bus.
func (i2c *I2C) writeByte(data byte) {
	// Write data to register.
	avr.TWDR.Set(data)

	// Clear TWI interrupt flag and enable TWI.
	avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT)

	// Wait till data is transmitted.
	for !avr.TWCR.HasBits(avr.TWCR_TWINT) {
	}
}

// readByte reads a single byte from the I2C bus.
func (i2c *I2C) readByte() byte {
	// Clear TWI interrupt flag and enable TWI.
	avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWEA)

	// Wait till read request is transmitted.
	for !avr.TWCR.HasBits(avr.TWCR_TWINT) {
	}

	return byte(avr.TWDR.Get())
}

// UART
var (
	// UART0 is the hardware serial port on the AVR.
	UART0 = UART{Buffer: NewRingBuffer()}
)

// UART on the AVR.
type UART struct {
	Buffer *RingBuffer
}

// Configure the UART on the AVR. Defaults to 9600 baud on Arduino.
func (uart UART) Configure(config UARTConfig) {
	if config.BaudRate == 0 {
		config.BaudRate = 9600
	}

	// Register the UART interrupt.
	interrupt.New(irq_USART0_RX, func(intr interrupt.Interrupt) {
		// Read register to clear it.
		data := avr.UDR0.Get()

		// Ensure no error.
		if !avr.UCSR0A.HasBits(avr.UCSR0A_FE0 | avr.UCSR0A_DOR0 | avr.UCSR0A_UPE0) {
			// Put data from UDR register into buffer.
			UART0.Receive(byte(data))
		}
	})

	// Set baud rate based on prescale formula from
	// https://www.microchip.com/webdoc/AVRLibcReferenceManual/FAQ_1faq_wrong_baud_rate.html
	// ((F_CPU + UART_BAUD_RATE * 8L) / (UART_BAUD_RATE * 16L) - 1)
	ps := ((CPUFrequency()+config.BaudRate*8)/(config.BaudRate*16) - 1)
	avr.UBRR0H.Set(uint8(ps >> 8))
	avr.UBRR0L.Set(uint8(ps & 0xff))

	// enable RX, TX and RX interrupt
	avr.UCSR0B.Set(avr.UCSR0B_RXEN0 | avr.UCSR0B_TXEN0 | avr.UCSR0B_RXCIE0)

	// 8-bits data
	avr.UCSR0C.Set(avr.UCSR0C_UCSZ01 | avr.UCSR0C_UCSZ00)
}

// WriteByte writes a byte of data to the UART.
func (uart UART) WriteByte(c byte) error {
	// Wait until UART buffer is not busy.
	for !avr.UCSR0A.HasBits(avr.UCSR0A_UDRE0) {
	}
	avr.UDR0.Set(c) // send char
	return nil
}

// SPIConfig is used to store config info for SPI.
type SPIConfig struct {
	Frequency uint32
	LSBFirst  bool
	Mode      uint8
}

// SPI is for the Serial Peripheral Interface
// Data is taken from http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf page 169 and following
type SPI struct {
	// The registers for the SPIx port set by the chip
	spcr *volatile.Register8
	spdr *volatile.Register8
	spsr *volatile.Register8

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

// Configure is intended to setup the SPI interface.
func (s SPI) Configure(config SPIConfig) error {

	// This is only here to help catch a bug with the configuration
	// where a machine missed a value.
	if s.spcr == (*volatile.Register8)(unsafe.Pointer(uintptr(0))) ||
		s.spsr == (*volatile.Register8)(unsafe.Pointer(uintptr(0))) ||
		s.spdr == (*volatile.Register8)(unsafe.Pointer(uintptr(0))) ||
		s.sck == 0 || s.sdi == 0 || s.sdo == 0 || s.cs == 0 {
		return errSPIInvalidMachineConfig
	}

	// Make the defaults meaningful
	if config.Frequency == 0 {
		config.Frequency = 4000000
	}

	// Default all port configuration bits to 0 for simplicity
	s.spcr.Set(0)
	s.spsr.Set(0)

	// Setup pins output configuration
	s.sck.Configure(PinConfig{Mode: PinOutput})
	s.sdi.Configure(PinConfig{Mode: PinInput})
	s.sdo.Configure(PinConfig{Mode: PinOutput})

	// Prevent CS glitches if the pin is enabled Low (0, default)
	s.cs.High()
	// If the CS pin is not configured as output the SPI port operates in
	// slave mode.
	s.cs.Configure(PinConfig{Mode: PinOutput})

	frequencyDivider := CPUFrequency() / config.Frequency

	switch {
	case frequencyDivider >= 128:
		s.spcr.SetBits(avr.SPCR_SPR0 | avr.SPCR_SPR1)
	case frequencyDivider >= 64:
		s.spcr.SetBits(avr.SPCR_SPR1)
	case frequencyDivider >= 32:
		s.spcr.SetBits(avr.SPCR_SPR1)
		s.spsr.SetBits(avr.SPSR_SPI2X)
	case frequencyDivider >= 16:
		s.spcr.SetBits(avr.SPCR_SPR0)
	case frequencyDivider >= 8:
		s.spcr.SetBits(avr.SPCR_SPR0)
		s.spsr.SetBits(avr.SPSR_SPI2X)
	case frequencyDivider >= 4:
		// The clock is already set to all 0's.
	default: // defaults to fastest which is /2
		s.spsr.SetBits(avr.SPSR_SPI2X)
	}

	switch config.Mode {
	case Mode1:
		s.spcr.SetBits(avr.SPCR_CPHA)
	case Mode2:
		s.spcr.SetBits(avr.SPCR_CPOL)
	case Mode3:
		s.spcr.SetBits(avr.SPCR_CPHA | avr.SPCR_CPOL)
	default: // default is mode 0
	}

	if config.LSBFirst {
		s.spcr.SetBits(avr.SPCR_DORD)
	}

	// enable SPI, set controller, set clock rate
	s.spcr.SetBits(avr.SPCR_SPE | avr.SPCR_MSTR)

	return nil
}

// Transfer writes the byte into the register and returns the read content
func (s SPI) Transfer(b byte) (byte, error) {
	s.spdr.Set(uint8(b))

	for !s.spsr.HasBits(avr.SPSR_SPIF) {
	}

	return byte(s.spdr.Get()), nil
}