// +build stm32,stm32f103xx

package runtime

import (
	"device/arm"
	"device/stm32"
	"machine"
	"runtime/interrupt"
	"runtime/volatile"
)

func init() {
	initCLK()
	initRTC()
	initTIM()
	machine.UART0.Configure(machine.UARTConfig{})
}

func putchar(c byte) {
	machine.UART0.WriteByte(c)
}

// initCLK sets clock to 72MHz using HSE 8MHz crystal w/ PLL X 9 (8MHz x 9 = 72MHz).
func initCLK() {
	stm32.FLASH.ACR.SetBits(stm32.FLASH_ACR_LATENCY_2)    // Two wait states, per datasheet
	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PPRE1_DIV_2)    // prescale PCLK1 = HCLK/2
	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PPRE2_DIV_NONE) // prescale PCLK2 = HCLK/1
	stm32.RCC.CR.SetBits(stm32.RCC_CR_HSEON)              // enable HSE clock

	// wait for the HSEREADY flag
	for !stm32.RCC.CR.HasBits(stm32.RCC_CR_HSERDY) {
	}

	stm32.RCC.CR.SetBits(stm32.RCC_CR_HSION) // enable HSI clock

	// wait for the HSIREADY flag
	for !stm32.RCC.CR.HasBits(stm32.RCC_CR_HSIRDY) {
	}

	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PLLSRC)   // set PLL source to HSE
	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_PLLMUL_9) // multiply by 9
	stm32.RCC.CR.SetBits(stm32.RCC_CR_PLLON)        // enable the PLL

	// wait for the PLLRDY flag
	for !stm32.RCC.CR.HasBits(stm32.RCC_CR_PLLRDY) {
	}

	stm32.RCC.CFGR.SetBits(stm32.RCC_CFGR_SW_PLL) // set clock source to pll

	// wait for PLL to be CLK
	for !stm32.RCC.CFGR.HasBits(stm32.RCC_CFGR_SWS_PLL) {
	}
}

const tickMicros = 1000

var (
	timestamp        timeUnit // microseconds since boottime
	timerLastCounter uint64
)

var timerWakeup volatile.Register8

func initRTC() {
	// Enable the PWR and BKP.
	stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_PWREN | stm32.RCC_APB1ENR_BKPEN)

	// access to backup register
	stm32.PWR.CR.SetBits(stm32.PWR_CR_DBP)

	// Enable LSE
	stm32.RCC.BDCR.SetBits(stm32.RCC_BDCR_LSEON)

	// wait until LSE is ready
	for !stm32.RCC.BDCR.HasBits(stm32.RCC_BDCR_LSERDY) {
	}

	// Select LSE
	stm32.RCC.BDCR.SetBits(stm32.RCC_RTCCLKSource_LSE)

	// set prescaler to "max" per datasheet
	stm32.RTC.PRLH.Set(stm32.RTC_PRLH_PRLH_Msk)
	stm32.RTC.PRLL.Set(stm32.RTC_PRLL_PRLL_Msk)

	// set count to zero
	stm32.RTC.CNTH.Set(0x0)
	stm32.RTC.CNTL.Set(0x0)

	// Enable RTC
	stm32.RCC.BDCR.SetBits(stm32.RCC_BDCR_RTCEN)

	// Clear RSF
	stm32.RTC.CRL.ClearBits(stm32.RTC_CRL_RSF)

	// Wait till flag is set
	for !stm32.RTC.CRL.HasBits(stm32.RTC_CRL_RSF) {
	}
}

// Enable the TIM3 clock.
func initTIM() {
	stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_TIM3EN)

	intr := interrupt.New(stm32.IRQ_TIM3, handleTIM3)
	intr.SetPriority(0xc3)
	intr.Enable()
}

const asyncScheduler = false

// sleepTicks should sleep for specific number of microseconds.
func sleepTicks(d timeUnit) {
	for d != 0 {
		ticks()            // update timestamp
		ticks := uint32(d) // current scaling only supports 100 usec to 6553 msec
		timerSleep(ticks)
		d -= timeUnit(ticks)
	}
}

// number of ticks (microseconds) since start.
func ticks() timeUnit {
	// convert RTC counter from seconds to microseconds
	timerCounter := uint64(stm32.RTC.CNTH.Get()<<16|stm32.RTC.CNTL.Get()) * 1000 * 1000

	// add the fractional part of current time using DIV register
	timerCounter += uint64(0x8000-stm32.RTC.DIVL.Get()) * 31

	// change since last measurement
	offset := (timerCounter - timerLastCounter)
	timerLastCounter = timerCounter
	timestamp += timeUnit(offset)
	return timestamp
}

// ticks are in microseconds
func timerSleep(ticks uint32) {
	timerWakeup.Set(0)

	// STM32 timer update event period is calculated as follows:
	//
	// 			Update_event = TIM_CLK/((PSC + 1)*(ARR + 1)*(RCR + 1))
	//
	// Where:
	//
	//			TIM_CLK = timer clock input
	// 			PSC = 16-bit prescaler register
	// 			ARR = 16/32-bit Autoreload register
	// 			RCR = 16-bit repetition counter
	//
	// Example:
	//
	//			TIM_CLK = 72 MHz
	// 			Prescaler = 1
	// 			Auto reload = 65535
	// 			No repetition counter RCR = 0
	// 			Update_event = 72*(10^6)/((1 + 1)*(65535 + 1)*(1))
	// 			Update_event = 549.3 Hz
	//
	// Set the timer prescaler/autoreload timing registers.

	// TODO: support smaller or larger scales (autoscaling) based
	// on the length of sleep time requested.
	// The current scaling only supports a range of 200 usec to 6553 msec.

	// prescale counter down from 72mhz to 10khz aka 0.1 ms frequency.
	stm32.TIM3.PSC.Set(machine.CPUFrequency()/10000 - 1) // 7199

	// Set duty aka duration.
	// STM32 dividers use n-1, i.e. n counts from 0 to n-1.
	// As a result, with these prescaler settings,
	// the minimum allowed duration is 200 microseconds.
	if ticks < 200 {
		ticks = 200
	}
	stm32.TIM3.ARR.Set(ticks/100 - 1) // convert from microseconds to 0.1 ms

	// Enable the hardware interrupt.
	stm32.TIM3.DIER.SetBits(stm32.TIM_DIER_UIE)

	// Enable the timer.
	stm32.TIM3.CR1.SetBits(stm32.TIM_CR1_CEN)

	// wait till timer wakes up
	for timerWakeup.Get() == 0 {
		arm.Asm("wfi")
	}
}

func handleTIM3(interrupt.Interrupt) {
	if stm32.TIM3.SR.HasBits(stm32.TIM_SR_UIF) {
		// Disable the timer.
		stm32.TIM3.CR1.ClearBits(stm32.TIM_CR1_CEN)

		// clear the update flag
		stm32.TIM3.SR.ClearBits(stm32.TIM_SR_UIF)

		// timer was triggered
		timerWakeup.Set(1)
	}
}