Low-level routines in computer architecture refer to operations that interact directly with the hardware. These routines are typically written in assembly language and are crucial for managing hardware resources efficiently.
#Key Concepts:
BIOS Services:
- BIOS is firmware that initializes and manages data flow between the computer’s operating system and attached devices like hard disks, video cards, and keyboards.
- It provides a set of low-level routines that software can use to perform hardware-related tasks without needing to interact directly with the hardware.
Interrupts:
- BIOS functions are often accessed via software Interrupts (e.g.,
INT 0x10for video services).
Registers:
- Assembly instructions use CPU registers to pass parameters to BIOS functions. For example,
AHandALare registers used to specify function numbers and parameters.
Video Functions:
- Examples include setting up the cursor, getting cursor position, displaying characters, and getting video mode. These are accessed via
INT 0x10.
Hardware Detection:
- Functions like
INT 0x11are used for detecting hardware components.
Memory Functions:
- These routines help in determining memory size and configuration, accessed via interrupts like
INT 0x12andINT 0x15.
Other Functions:
- Include tasks like reading keyboard input, which can be done through
INT 0x16.
#Example Explained:
The assembly code snippet on the slide:
mov ah, 0x0e ; function number = 0Eh : Display Character mov al, '!' ; AL = code of character to display int 0x10 ; call INT 10h, BIOS video service
mov ah, 0x0e: Sets theAHregister to0x0E, specifying the function to display a character.mov al, '!': Loads theALregister with the ASCII code for the character!.int 0x10: Triggers the BIOS video service interrupt to execute the display character function. These low-level routines are essential for bootstrapping the system and providing basic input/output operations before the operating system takes over.
Interrupt