Syscalls

OpenDOS Syscalls Documentation (not implemented yet)

Overview

System calls (syscalls) in OpenDOS provide a controlled interface for user-space programs to request services from the kernel. They allow interaction with standard devices and system functions without giving direct access to kernel memory or hardware.

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Syscall Numbers

Number	Name	Description
0	SYS_INPUT	Read input from standard input (keyboard).
1	SYS_PRINT	Write a string to standard output (screen).
2	SYS_PRINTERR	Write a string to standard error (screen, red text).
5	SYS_EXIT	Terminate the current program.

⚠️ Note: Numbers are fixed and must be used by programs to request the correct service.

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Usage

General Structure

#include "syscalls.h"
uint32_t handle_syscall(uint32_t number, uint32_t arg1);

• number — syscall number.

• arg1 — argument, usually a pointer to a string or buffer, or a return code.

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Example: Printing Text

handle_syscall(SYS_PRINT, (uint32_t)"Hello, OpenDOS!\n");
handle_syscall(SYS_PRINTERR, (uint32_t)"Error message!\n");

• SYS_PRINT prints normally.

• SYS_PRINTERR prints in red using ANSI escape codes.

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Example: Reading Input

uint32_t c = handle_syscall(SYS_INPUT, 0);
// c contains the ASCII code of the pressed key

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Example: Exiting a Program

handle_syscall(SYS_EXIT, 0);

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Implementation Notes

1. All syscalls are handled by handle_syscall() in syscall.c.

2. Strings are printed using k_printf(), which supports ANSI escape codes for colored output.

3. SYS_PRINTERR outputs text in red by wrapping the string with \x1b[31m ... \x1b[0m.

4. Future syscalls can be added by extending the switch statement in handle_syscall() and assigning a new number.