126 строки
2,7 КиБ
Go
126 строки
2,7 КиБ
Go
// +build avr
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package runtime
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import (
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"device/avr"
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"unsafe"
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)
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const BOARD = "arduino"
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type timeUnit uint32
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var currentTime timeUnit
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const tickMicros = 1024 * 16384
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// Watchdog timer periods. These can be off by a large margin (hence the jump
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// between 64ms and 125ms which is not an exact double), so don't rely on this
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// for accurate time keeping.
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const (
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WDT_PERIOD_16MS = iota
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WDT_PERIOD_32MS
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WDT_PERIOD_64MS
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WDT_PERIOD_125MS
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WDT_PERIOD_250MS
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WDT_PERIOD_500MS
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WDT_PERIOD_1S
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WDT_PERIOD_2S
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)
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//go:extern _sbss
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var _sbss unsafe.Pointer
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//go:extern _ebss
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var _ebss unsafe.Pointer
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func preinit() {
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// Initialize .bss: zero-initialized global variables.
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ptr := uintptr(unsafe.Pointer(&_sbss))
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for ptr != uintptr(unsafe.Pointer(&_ebss)) {
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*(*uint8)(unsafe.Pointer(ptr)) = 0
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ptr += 1
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}
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}
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func postinit() {
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// Enable interrupts after initialization.
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avr.Asm("sei")
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}
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func init() {
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initUART()
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}
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func initUART() {
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// Initialize UART at 115200 baud when running at 16MHz.
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*avr.UBRR0H = 0
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*avr.UBRR0L = 8
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*avr.UCSR0B = avr.UCSR0B_RXEN0 | avr.UCSR0B_TXEN0 // enable RX and TX
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*avr.UCSR0C = avr.UCSR0C_UCSZ01 | avr.UCSR0C_UCSZ00 // 8-bits data
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}
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func putchar(c byte) {
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for (*avr.UCSR0A & avr.UCSR0A_UDRE0) == 0 {
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// Wait until previous char has been sent.
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}
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*avr.UDR0 = avr.RegValue(c) // send char
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}
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// Sleep this number of ticks of 16ms.
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//
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// TODO: not very accurate. Improve accuracy by calibrating on startup and every
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// once in a while.
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func sleepTicks(d timeUnit) {
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currentTime += d
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for d != 0 {
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sleepWDT(WDT_PERIOD_16MS)
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d -= 1
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}
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}
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// Sleep for a given period. The period is defined by the WDT peripheral, and is
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// on most chips (at least) 3 bits wide, in powers of two from 16ms to 2s
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// (0=16ms, 1=32ms, 2=64ms...). Note that the WDT is not very accurate: it can
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// be off by a large margin depending on temperature and supply voltage.
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//
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// TODO: disable more peripherals etc. to reduce sleep current.
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func sleepWDT(period uint8) {
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// Configure WDT
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avr.Asm("cli")
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avr.Asm("wdr")
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// Start timed sequence.
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*avr.WDTCSR |= avr.WDTCSR_WDCE | avr.WDTCSR_WDE
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// Enable WDT and set new timeout (0.5s)
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*avr.WDTCSR = avr.WDTCSR_WDIE | avr.RegValue(period)
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avr.Asm("sei")
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// Set sleep mode to idle and enable sleep mode.
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// Note: when using something other than idle, the UART won't work
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// correctly. This needs to be fixed, though, so we can truly sleep.
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*avr.SMCR = (0 << 1) | avr.SMCR_SE
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// go to sleep
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avr.Asm("sleep")
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// disable sleep
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*avr.SMCR = 0
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}
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func ticks() timeUnit {
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return currentTime
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}
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func abort() {
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avr.Asm("cli")
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for {
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sleepWDT(WDT_PERIOD_2S)
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}
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}
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// Align on a word boundary.
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func align(ptr uintptr) uintptr {
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// No alignment necessary on the AVR.
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return ptr
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}
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