// Initialise the interrupt descriptor table.
static ZLOX_VOID zlox_init_idt()
{   
...............................................
...............................................

    // Remap the irq table.
    // ICW1: starts the initialization sequence (in cascade mode)
    zlox_outb(0x20, 0x11);
    zlox_outb(0xA0, 0x11);
    // ICW2: Master PIC vector offset
    zlox_outb(0x21, 0x20);
    // ICW2: Slave PIC vector offset
    zlox_outb(0xA1, 0x28);
    // ICW3: tell Master PIC that there is a slave PIC at IRQ2 (0000 0100)
    zlox_outb(0x21, 0x04);
    // ICW3: tell Slave PIC its cascade identity (0000 0010)
    zlox_outb(0xA1, 0x02);
    // ICW4: 8086/88 (MCS-80/85) mode
    zlox_outb(0x21, 0x01);
    // ICW4: 8086/88 (MCS-80/85) mode
    zlox_outb(0xA1, 0x01);
    // masks.
    zlox_outb(0x21, 0x0);
    // masks.
    zlox_outb(0xA1, 0x0);

...............................................
...............................................

    zlox_idt_set_gate(ZLOX_IRQ0, (ZLOX_UINT32)_zlox_irq_0, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ1, (ZLOX_UINT32)_zlox_irq_1, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ2, (ZLOX_UINT32)_zlox_irq_2, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ3, (ZLOX_UINT32)_zlox_irq_3, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ4, (ZLOX_UINT32)_zlox_irq_4, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ5, (ZLOX_UINT32)_zlox_irq_5, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ6, (ZLOX_UINT32)_zlox_irq_6, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ7, (ZLOX_UINT32)_zlox_irq_7, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ8, (ZLOX_UINT32)_zlox_irq_8, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ9, (ZLOX_UINT32)_zlox_irq_9, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ10, (ZLOX_UINT32)_zlox_irq_10, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ11, (ZLOX_UINT32)_zlox_irq_11, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ12, (ZLOX_UINT32)_zlox_irq_12, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ13, (ZLOX_UINT32)_zlox_irq_13, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ14, (ZLOX_UINT32)_zlox_irq_14, 0x08, 0x8E);
    zlox_idt_set_gate(ZLOX_IRQ15, (ZLOX_UINT32)_zlox_irq_15, 0x08, 0x8E);

...............................................
...............................................
}

................................
................................

.macro _ZLOX_INT_IRQ irqNum intNum
.global _zlox_irq_\irqNum
_zlox_irq_\irqNum:
	cli
	pushl $0
	pushl $\intNum
	jmp _zlox_irq_common_stub
.endm

................................
................................

_ZLOX_INT_IRQ	0,	32
_ZLOX_INT_IRQ	1,	33
_ZLOX_INT_IRQ	2,	34
_ZLOX_INT_IRQ	3,	35
_ZLOX_INT_IRQ	4,	36
_ZLOX_INT_IRQ	5,	37
_ZLOX_INT_IRQ	6,	38
_ZLOX_INT_IRQ	7,	39
_ZLOX_INT_IRQ	8,	40
_ZLOX_INT_IRQ	9,	41
_ZLOX_INT_IRQ	10,	42
_ZLOX_INT_IRQ	11,	43
_ZLOX_INT_IRQ	12,	44
_ZLOX_INT_IRQ	13,	45
_ZLOX_INT_IRQ	14,	46
_ZLOX_INT_IRQ	15,	47

................................
................................

# This is our common IRQ stub. It saves the processor state, sets
# up for kernel mode segments, calls the C-level fault handler,
# and finally restores the stack frame.
_zlox_irq_common_stub:
	pusha		# Pushes edi,esi,ebp,esp,ebx,edx,ecx,eax

	movw %ds,%ax	# Lower 16-bits of eax = ds.
	pushl %eax	# save the data segment descriptor

	movw $0x10,%ax	# load the kernel data segment descriptor
	movw %ax,%ds
	movw %ax,%es
	movw %ax,%fs
	movw %ax,%gs

	call zlox_irq_handler	# in zlox_isr.c

	pop %ebx		# reload the original data segment descriptor
	movw %bx,%ds
	movw %bx,%es
	movw %bx,%fs
	movw %bx,%gs

	popa		# Pops edi,esi,ebp...
	addl $8,%esp	# Cleans up the pushed error code and pushed ISR number
	sti
	iret		# pops 5 things at once: CS, EIP, EFLAGS, SS, and ESP

ZLOX_ISR_CALLBACK interrupt_callbacks[256];

..........................................
..........................................

// This gets called from our ASM interrupt handler stub.
ZLOX_VOID zlox_irq_handler(ZLOX_ISR_REGISTERS regs)
{
    // Send an EOI (end of interrupt) signal to the PICs.
    // If this interrupt involved the slave.
    if (regs.int_no >= ZLOX_IRQ8)
    {
        // Send reset signal to slave.
        zlox_outb(0xA0, 0x20);
    }
	// Send reset signal to master. (As well as slave, if necessary).
        zlox_outb(0x20, 0x20);
	
	//zlox_monitor_write("zenglox recieved irq: ");
	//zlox_monitor_write_dec(regs.int_no);
	//zlox_monitor_put('\n');

    if (interrupt_callbacks[regs.int_no] != 0)
    {
        ZLOX_ISR_CALLBACK callback = interrupt_callbacks[regs.int_no];
        callback(regs);
    }
}

Bits         Usage
 6 and 7      Select channel :
                 0 0 = Channel 0
                 0 1 = Channel 1
                 1 0 = Channel 2
                 1 1 = Read-back command (8254 only)
 4 and 5      Access mode :
                 0 0 = Latch count value command
                 0 1 = Access mode: lobyte only
                 1 0 = Access mode: hibyte only
                 1 1 = Access mode: lobyte/hibyte
 1 to 3       Operating mode :
                 0 0 0 = Mode 0 (interrupt on terminal count)
                 0 0 1 = Mode 1 (hardware re-triggerable one-shot)
                 0 1 0 = Mode 2 (rate generator)
                 0 1 1 = Mode 3 (square wave generator)
                 1 0 0 = Mode 4 (software triggered strobe)
                 1 0 1 = Mode 5 (hardware triggered strobe)
                 1 1 0 = Mode 2 (rate generator, same as 010b)
                 1 1 1 = Mode 3 (square wave generator, same as 011b)
 0            BCD/Binary mode: 0 = 16-bit binary, 1 = four-digit BCD

/*zlox_kernel.c Defines the C-code kernel entry point, calls initialisation routines.*/

#include "zlox_monitor.h"
#include "zlox_descriptor_tables.h"
#include "zlox_time.h"

//zenglOX kernel main entry
ZLOX_SINT32 zlox_kernel_main(ZLOX_VOID * mboot_ptr)
{
	// init gdt and idt
	zlox_init_descriptor_tables();	

	// Initialise the screen (by clearing it)
	zlox_monitor_clear();
	 // Write out a sample string
	zlox_monitor_write("hello world!\nwelcome to zenglOX v0.0.4!\n");

	asm volatile("int $0x3");
        asm volatile("int $0x4");
	
	asm volatile("sti");
	zlox_init_timer(50);

	return (ZLOX_SINT32)mboot_ptr;
}