157 строки
4,2 КиБ
Go
157 строки
4,2 КиБ
Go
// +build avr,atmega
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package machine
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import (
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"device/avr"
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"runtime/interrupt"
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)
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// I2CConfig is used to store config info for I2C.
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type I2CConfig struct {
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Frequency uint32
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}
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// Configure is intended to setup the I2C interface.
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func (i2c I2C) Configure(config I2CConfig) {
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// Default I2C bus speed is 100 kHz.
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if config.Frequency == 0 {
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config.Frequency = TWI_FREQ_100KHZ
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}
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// Activate internal pullups for twi.
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avr.PORTC.SetBits((avr.DIDR0_ADC4D | avr.DIDR0_ADC5D))
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// Initialize twi prescaler and bit rate.
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avr.TWSR.SetBits((avr.TWSR_TWPS0 | avr.TWSR_TWPS1))
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// twi bit rate formula from atmega128 manual pg. 204:
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// SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
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// NOTE: TWBR should be 10 or higher for controller mode.
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// It is 72 for a 16mhz board with 100kHz TWI
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avr.TWBR.Set(uint8(((CPUFrequency() / config.Frequency) - 16) / 2))
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// Enable twi module.
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avr.TWCR.Set(avr.TWCR_TWEN)
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}
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// Tx does a single I2C transaction at the specified address.
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// It clocks out the given address, writes the bytes in w, reads back len(r)
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// bytes and stores them in r, and generates a stop condition on the bus.
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func (i2c I2C) Tx(addr uint16, w, r []byte) error {
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if len(w) != 0 {
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i2c.start(uint8(addr), true) // start transmission for writing
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for _, b := range w {
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i2c.writeByte(b)
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}
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}
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if len(r) != 0 {
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i2c.start(uint8(addr), false) // re-start transmission for reading
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for i := range r { // read each char
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r[i] = i2c.readByte()
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}
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}
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if len(w) != 0 || len(r) != 0 {
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// Stop the transmission after it has been started.
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i2c.stop()
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}
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return nil
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}
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// start starts an I2C communication session.
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func (i2c I2C) start(address uint8, write bool) {
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// Clear TWI interrupt flag, put start condition on SDA, and enable TWI.
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avr.TWCR.Set((avr.TWCR_TWINT | avr.TWCR_TWSTA | avr.TWCR_TWEN))
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// Wait till start condition is transmitted.
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for !avr.TWCR.HasBits(avr.TWCR_TWINT) {
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}
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// Write 7-bit shifted peripheral address.
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address <<= 1
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if !write {
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address |= 1 // set read flag
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}
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i2c.writeByte(address)
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}
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// stop ends an I2C communication session.
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func (i2c I2C) stop() {
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// Send stop condition.
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avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWSTO)
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// Wait for stop condition to be executed on bus.
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for !avr.TWCR.HasBits(avr.TWCR_TWSTO) {
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}
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}
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// writeByte writes a single byte to the I2C bus.
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func (i2c I2C) writeByte(data byte) {
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// Write data to register.
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avr.TWDR.Set(data)
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// Clear TWI interrupt flag and enable TWI.
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avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT)
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// Wait till data is transmitted.
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for !avr.TWCR.HasBits(avr.TWCR_TWINT) {
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}
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}
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// readByte reads a single byte from the I2C bus.
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func (i2c I2C) readByte() byte {
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// Clear TWI interrupt flag and enable TWI.
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avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWEA)
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// Wait till read request is transmitted.
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for !avr.TWCR.HasBits(avr.TWCR_TWINT) {
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}
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return byte(avr.TWDR.Get())
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}
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// UART on the AVR.
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type UART struct {
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Buffer *RingBuffer
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}
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// Configure the UART on the AVR. Defaults to 9600 baud on Arduino.
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func (uart UART) Configure(config UARTConfig) {
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if config.BaudRate == 0 {
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config.BaudRate = 9600
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}
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// Register the UART interrupt.
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interrupt.New(irq_USART0_RX, func(intr interrupt.Interrupt) {
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// Read register to clear it.
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data := avr.UDR0.Get()
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// Ensure no error.
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if !avr.UCSR0A.HasBits(avr.UCSR0A_FE0 | avr.UCSR0A_DOR0 | avr.UCSR0A_UPE0) {
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// Put data from UDR register into buffer.
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UART0.Receive(byte(data))
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}
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})
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// Set baud rate based on prescale formula from
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// https://www.microchip.com/webdoc/AVRLibcReferenceManual/FAQ_1faq_wrong_baud_rate.html
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// ((F_CPU + UART_BAUD_RATE * 8L) / (UART_BAUD_RATE * 16L) - 1)
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ps := ((CPUFrequency()+config.BaudRate*8)/(config.BaudRate*16) - 1)
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avr.UBRR0H.Set(uint8(ps >> 8))
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avr.UBRR0L.Set(uint8(ps & 0xff))
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// enable RX, TX and RX interrupt
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avr.UCSR0B.Set(avr.UCSR0B_RXEN0 | avr.UCSR0B_TXEN0 | avr.UCSR0B_RXCIE0)
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// 8-bits data
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avr.UCSR0C.Set(avr.UCSR0C_UCSZ01 | avr.UCSR0C_UCSZ00)
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}
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// WriteByte writes a byte of data to the UART.
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func (uart UART) WriteByte(c byte) error {
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// Wait until UART buffer is not busy.
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for !avr.UCSR0A.HasBits(avr.UCSR0A_UDRE0) {
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}
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avr.UDR0.Set(c) // send char
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return nil
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}
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