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Hardware Drivers Reference

This document provides a technical overview of the hardware drivers implemented in TilekarOS.

1. VGA & TTY Driver

Source Files: tty.c, vga.h

The VGA driver manages the text-mode buffer at 0xB8000.

Features:

  • Scrolling: Moves the entire screen up when the bottom is reached.
  • Color Support: Supports 16 foreground and 16 background colors.
  • Hardware Cursor: Updates the blinking underscore using VGA I/O ports.
  • Serial Logging: Mirrors all output to the COM1 Serial Port (0x3F8) for easy debugging.

2. PS/2 Keyboard Driver

Source Files: keyboard.c, keyboard.h

The keyboard driver handles input from a standard PS/2 keyboard using IRQ 1.

Features:

  • Scancode Mapping: Translates raw PS/2 Set 1 scancodes into ASCII characters.
  • Modifier Tracking: Tracks the state of Shift, Ctrl, Alt, and Caps Lock.
  • Buffer API: Provides keyboard_getchar() which yields until a key is pressed.

3. Programmable Interval Timer (PIT)

Source Files: timer.c, timer.h

The PIT generates periodic interrupts at a fixed frequency (default: 1000Hz).

The Trigger System:

TilekarOS features a "Trigger" system that allows functions to be scheduled to run every X ticks. - Preemption: The scheduler uses a trigger to preempt tasks every 100ms. - Timekeeping: Global ticks counter since boot.

4. PCI Bus Driver

Source Files: pci.c, pci.h

The PCI driver enumerates devices on the PCI bus using I/O ports 0xCF8 (Address) and 0xCFC (Data).

Features:

  • Device Enumeration: Scans all 32 devices on each of the 256 buses.
  • Vendor/Device ID: Identifies hardware manufacturers and models.
  • Class/Subclass: Determines device types (e.g., Storage Controller, Display Adapter).

5. ATA (IDE) Disk Driver

Source Files: ata.c, ata.h

The ATA driver provides access to IDE hard drives using both PIO (Programmed I/O) and DMA (Direct Memory Access) modes.

Features:

  • LBA28 Support: Supports disks up to 128GB.
  • Bus Master DMA: Uses the PCI Bus Master IDE (BMIDE) interface for high-speed transfers.
  • PRDT Management: Automatically manages Physical Region Descriptor Tables for DMA transfers.
  • Interrupt Driven: Uses IRQ 14 (Primary) and IRQ 15 (Secondary) for asynchronous completion.
  • Fallback Mechanism: Automatically falls back to PIO mode if DMA is unavailable.

DMA Implementation:

  1. PCI Configuration: The kernel enables "Bus Mastering" in the PCI Command register for the IDE controller.
  2. PRDT Setup: A Physical Region Descriptor Table is prepared, pointing to a physically contiguous DMA buffer.
  3. BMIDE Control: The BMIDE Command register is used to start/stop the transfer, while the Status register reports completion or errors.

References