Having problem setting up my timer ISR

[cfowler]

I'm trying to learn the internals of an OS so I thought I woudl write a kernel.  This has proven to be a difficult project.  I'm using bootmaker to boot my elf kernel but am having difficuly setting up my Timer isr.

The first thing I do is intialize the PIC
init_pic() {
    cli();
    /* Initialize Master 8259 PIC */
    outportb(0x20, 0x11);   /* ICW1 - Edge Triggered Mode, Cascaded PIC,   */
                            /*        ICW4 required to define uPM          */
    outportb(0x21, 0x08);   /* ICW2 - Set PIC offset to 08h, the PC's      */
                            /*        Master PIC IVT base address          */
    outportb(0x21, 0x04);   /* ICW3 - Slave PIC attached to IR2 Input      */
    outportb(0x21, 0x01);   /* ICW4 - Set PIC operation to 8086/8088 Mode  */
    outportb(0x21, 0xFe);   /* OCW1 - Disable interrupts for all IRQs    */

    /* Intialize Slave 8259 PIC */
    outportb(0xa0, 0x11);   /* ICW1 - Edge Triggered Mode, Cascaded PIC,   */
                            /*        ICW4 required to define uPM          */
    outportb(0xa1, 0x70);   /* ICW2 - Set PIC offset to 70h, the PC's      */
                            /*        Slave PIC IVT base address           */
    outportb(0xa1, 0x02);   /* ICW3 - Slave PIC ID = 2, the IRx level it   */
                            /*        occupies on the Master PIC           */
    outportb(0xa1, 0x01);   /* ICW4 - Set PIC operation to 8086/8088 Mode  */
    outportb(0xa1, 0xFF);   /* OCW1 - Disable interrupts for all IRQs     */

    // Debugging info
    printf("Interrutps enabled on PIC1: 0x%x\n", inb(0x21));
    printf("Interrutps enabled on PIC2: 0x%x\n", inb(0xA1));
    sti();
}


I'm getting error handlers to work but whenever I try to setup the timer isr, I get a boud exception
Im the remap_pics example aove I set the offset to 0x08 but I'm not sure if I have anythnig there.  Is there somthing I'm totally missing here?  I started out with the DemoOS.

Thanks,
Chris

[Adek336]

I'm also new to this stuff. Correct me if I'm wrong, but I think that the PIC should usually not overlap first 32 ints, which are exceptions.

Instead of
outportb(0x21, 0x08);   /* ICW2 - Set PIC offset to 08h, the PC's      */
                            /*        Master PIC IVT base address          */

try outportb(0x21, 0x20);

Hope this helps,
Adrian.