pic.go

package main

const (
	PIC_PRINT_DEBUG = ENABLE_DEBUG

	PIC1Port uint16 = 0x20
	PIC1Data uint16 = PIC1Port + 1
	PIC2Port uint16 = 0xA0
	PIC2Data uint16 = PIC2Port + 1

	PIC1Offset byte = 0x20
	PIC2Offset byte = 0x28

	PIC_ICW1_ICW4 byte = 0x01 // ICW4 will be sent
	PIC_ICW1_Init byte = 0x10
	PIC_ICW4_8086 byte = 0x01 // Set 8086/88 mode. unset MCS-80/85 mode

	PIC_EOI     byte = 0x20 // End of interrupt
	PIC_ReadIRR byte = 0xa
	PIC_ReadISR byte = 0xb
)

var picHandlers [16]func()

func PICInterruptHandler() {
	info := &currentThread.info
	if currentThread.isKernelInterrupt {
		info = &currentThread.kernelInfo
	}
	irq := info.InterruptNumber - uint32(PIC1Offset)
	if irq == 7 {
		Outb(PIC1Port, PIC_ReadISR)
		res := Inb(PIC1Port)
		if res&(1<<7) == 0 {
			// Spurious IRQ
			return
		}
	}
	if irq == 15 {
		Outb(PIC1Port, PIC_ReadISR)
		res := Inb(PIC1Port)
		if res&(1<<7) == 0 {
			// Spurious IRQ
			// PIC1 does not know it is spurious
			Outb(PIC1Port, PIC_EOI)
			return
		}
	}

	if PIC_PRINT_DEBUG && irq != 0 {
		kdebugln("[PIC] Handler nr ", irq)
	}
	picHandlers[irq]()

	if irq >= 8 {
		Outb(PIC2Port, PIC_EOI)
	}
	Outb(PIC1Port, PIC_EOI)
}

func defaultPicHandler() {
	kerrorln("Unhandled IRQ")
}

func InitPIC() {

	Outb(PIC1Port, PIC_ICW1_Init|PIC_ICW1_ICW4)
	Outb(PIC2Port, PIC_ICW1_Init|PIC_ICW1_ICW4)

	Outb(PIC1Data, PIC1Offset)
	Outb(PIC2Data, PIC2Offset)

	Outb(PIC1Data, 0b0100) // Tells PIC1 that there is slave PIC at IRQ2
	Outb(PIC2Data, 2)      // Tells slave PIC what IRQ it is on master PIC (binary form)
	Outb(PIC1Data, PIC_ICW4_8086)
	Outb(PIC2Data, PIC_ICW4_8086)

	Outb(PIC1Data, 0xff)
	Outb(PIC2Data, 0xff)

	for i := 0; i < 8; i++ {
		SetInterruptHandler(PIC1Offset+byte(i), PICInterruptHandler, KCS_SELECTOR, PRIV_USER)
	}
	for i := 0; i < 8; i++ {
		SetInterruptHandler(PIC2Offset+byte(i), PICInterruptHandler, KCS_SELECTOR, PRIV_USER)
	}
	for i := range picHandlers {
		RegisterPICHandler(uint8(i), defaultPicHandler)
	}
}

func DisableIRQ(irq uint8) {
	port := PIC1Data
	if irq > 7 {
		port = PIC2Data
		irq -= 8
	}
	value := Inb(port) | (1 << irq)
	Outb(port, value)
}

func EnableIRQ(irq uint8) {
	port := PIC1Data
	if irq > 7 {
		port = PIC2Data
		irq -= 8
	}
	value := Inb(port) &^ (1 << irq)
	Outb(port, value)
}

func RegisterPICHandler(irq uint8, f func()) {
	if irq > 15 {
		kernelPanic("[PIC] The requested irq does not exist")
	}
	picHandlers[irq] = f
}