asm part calls _kmain. kmain() starts execution now.
(bootloader setups GDT with null ,linear code & data descriptors.
es=fs=gs=ds = ss = 0x10 i.e. linear data seg.desc. by bootloader.)
do i need to setup a TSS first? is it because of no TSS.
Please let me know what goes wrong.
here is the code ....
// kernel.c
#include "global.h" // prototype declaration & data structure defn.
static INT_DESCRIPTOR idt[0x31];
static IDT_REG idtr;
kmain()
{
setup_IDT();
setup_PIC();
enable_IRQ(1); // enable keyboard interrupt.
asm("sti"): // restarts now.....
}
// if asm("hlt"); is placed between enable_IRQ(1); & asm("sti"), it hangs.
// I changed the sequence of sti & enable_IRQ. (no asm("hlt"); in between)
// now it restarts on enable_IRQ(1). I tested this again by plasing "hlt "
//between them.
void serup_IDT()
{
dword i;
memset (&idt, 0, sizeof(idt)); //... ok
// Int 0Dh - General Protection Fault Handler
idt[0x0D].offs0_15 = ((dword)(&gpf_isr))&0xFFFF;
idt[0x0D].offs16_31 = ((dword)(&gpf_isr)) >> 16;
idt[0x0D].sel = 8;
idt[0x0D].paramcnt = 0;
idt[0x0D].attrs = ACS_INT_GATE;
// IRQ0...0Fh
for (i=0;i<16;i++)
{
idt[0x20+i].sel = 8;
idt[0x20+i].paramcnt = 0;
idt[0x20+i].attrs = ACS_INT_GATE;
idt[0x20+i].offs0_15 = ((dword)(&demo_isr))&0xFFFF;
idt[0x20+i].offs16_31 = ((dword)(&demo_isr))>> 16;
}
idt[0x20].offs0_15 = ((dword)(&timer_isr))&0xFFFF;
idt[0x20].offs16_31 = ((dword)(&timer_isr)) >> 16;
idt[0x21].offs0_15 = ((dword)(&kb_isr))&0xFFFF;
idt[0x21].offs16_31 = ((dword)(&kb_isr)) >> 16;
idtr.base = (dword) &idt;
idtr.limit = sizeof(idt)-1;
LIDT (&idtr); // asm routine ,works correctly.
}
void setup_pic()
{
remap_pic(0x20,0x28);
set_IRQ_mask(0xff);
}
void remap_pic(byte master_vector, byte slave_vector)
{
outportb (PORT_8259_M, 0x11); /* start 8259 initialization */
outportb (PORT_8259_S, 0x11);
outportb (PORT_8259_M+1, master_vector); /* master base interrupt vector */
outportb (PORT_8259_S+1, slave_vector); /* slave base interrupt vector */
outportb (PORT_8259_M+1, 1<<2); /* bitmask for cascade on IRQ2 */
outportb (PORT_8259_S+1, 2); /* cascade on IRQ2 */
outportb (PORT_8259_M+1, 1); /* finish 8259 initialization */
outportb (PORT_8259_S+1, 1);
}
void set_IRQ_mask (dword IRQ_mask)
{
outportb (PORT_INT_MASK_M, IRQ_mask & 0xFF);
outportb (PORT_INT_MASK_S, IRQ_mask >>
;}
// here is asm part :
GLOBAL _kb_isr,_demo_isr,_timer_isr
EXTERN _kb_handler,_demo_handler,_timer_handler
_kb_isr:
pushad
call _kb_handler
popad
iret
_demo_isr:
pushad
call _demo_handler
popad
iret
_timer_isr:
pushad
call _timer_handler
popad
iret
Thanks in advance.