// +build avr

package runtime

import (
	"device/avr"
)

const BOARD = "arduino"

const Microsecond = 1

var currentTime uint64

func init() {
	currentTime = 0
}

// Watchdog timer periods. These can be off by a large margin (hence the jump
// between 64ms and 125ms which is not an exact double), so don't rely on this
// for accurate time keeping.
const (
	WDT_PERIOD_16MS = iota
	WDT_PERIOD_32MS
	WDT_PERIOD_64MS
	WDT_PERIOD_125MS
	WDT_PERIOD_250MS
	WDT_PERIOD_500MS
	WDT_PERIOD_1S
	WDT_PERIOD_2S
)

func init() {
	initUART()
}

func initUART() {
	// Initialize UART at 115200 baud when running at 16MHz.
	avr.USART.UBRR0H = 0
	avr.USART.UBRR0L = 8
	avr.USART.UCSR0B = avr.UCSR0B_RXEN0 | avr.UCSR0B_TXEN0 // enable RX and TX
	avr.USART.UCSR0C = avr.UCSR0C_UCSZ0                    // 8-bits data
}

func putchar(c byte) {
	for (avr.USART.UCSR0A & avr.UCSR0A_UDRE0) == 0 {
		// Wait until previous char has been sent.
	}
	avr.USART.UDR0 = avr.RegValue(c) // send char
}

// Sleep by the given amount.
//
// TODO: not very accurate. Improve accuracy by calibrating on startup and every
// once in a while.
func sleep(d Duration) {
	currentTime += uint64(d)
	d /= 16384 // about 16ms
	for d != 0 {
		sleepWDT(WDT_PERIOD_16MS)
		d -= 1
	}
}

// Sleep for a given period. The period is defined by the WDT peripheral, and is
// on most chips (at least) 3 bits wide, in powers of two from 16ms to 2s
// (0=16ms, 1=32ms, 2=64ms...). Note that the WDT is not very accurate: it can
// be off by a large margin depending on temperature and supply voltage.
//
// TODO: disable more peripherals etc. to reduce sleep current.
func sleepWDT(period uint8) {
	// Configure WDT
	avr.Asm("cli")
	avr.Asm("wdr")
	// Start timed sequence.
	avr.WDT.WDTCSR |= avr.WDTCSR_WDCE | avr.WDTCSR_WDE
	// Enable WDT and set new timeout (0.5s)
	avr.WDT.WDTCSR = avr.WDTCSR_WDIE | avr.RegValue(period)
	avr.Asm("sei")

	// Set sleep mode to idle and enable sleep mode.
	// Note: when using something other than idle, the UART won't work
	// correctly. This needs to be fixed, though, so we can truly sleep.
	avr.CPU.SMCR = (0 << 1) | avr.SMCR_SE

	// go to sleep
	avr.Asm("sleep")

	// disable sleep
	avr.CPU.SMCR = 0
}

func monotime() uint64 {
	return currentTime
}

func abort() {
	avr.Asm("cli")
	for {
		sleepWDT(WDT_PERIOD_2S)
	}
}

// Align on a word boundary.
func align(ptr uintptr) uintptr {
	// No alignment necessary on the AVR.
	return ptr
}