Implement PIO-mode IDE driver that scans primary and secondary channels
for ATA hard drives and ATAPI CD/DVD drives using IDENTIFY commands.
Features:
- Scans 4 possible devices (2 channels x 2 drives each)
- ATA IDENTIFY DEVICE for hard drives
- ATAPI IDENTIFY PACKET DEVICE for CD/DVD drives
- PIO-mode 28-bit LBA sector read/write for ATA drives
- Model string extraction and sector count parsing
- Registers as kernel driver via REGISTER_DRIVER macro
- Registers devices with devicefs: ATA → hdd class, ATAPI → cd class
- Added inw/outw to port_io.h for 16-bit I/O
Tested: QEMU detects hdd1 (QEMU HARDDISK) and cd1 (QEMU DVD-ROM).
- Reworked IDT initialization to register all 32 CPU exception handlers (ISR 0-31)
and 16 hardware interrupt handlers (IRQ 0-15, mapped to IDT entries 32-47).
- Created assembly stubs in interrupts.S using macros for ISRs with and without
error codes, plus IRQ stubs. All route through a common stub that saves
registers, loads kernel data segment, and calls the C handler.
- Added isr.c with a unified interrupt dispatcher that handles both exceptions
(halts on fault) and hardware IRQs (sends EOI via PIC).
- Implemented PIC (8259) driver in pic.c with full initialization sequence that
remaps IRQ 0-7 to IDT 32-39 and IRQ 8-15 to IDT 40-47. Includes mask/unmask
and EOI support.
- Extracted port I/O primitives (inb, outb, io_wait) into port_io.h header for
reuse across drivers.
- Kernel now initializes PIC after IDT and enables interrupts with STI.
