Syscall interface (INT 30h)

Programs loaded from the filesystem can use INT 30h for OS services. Syscall numbers are defined symbolically as SYS_* constants in src/include/constants.asm — programs reference the names, not the numbers.

AH	Name	Description
00h	fs_chmod	Set file flags, SI = filename, AL = flags, CF on err
01h	fs_mkdir	Create subdirectory, SI = name, AX = start sector, CF on err
02h	fs_rename	Rename or move file, SI = old name, DI = new name, CF on err
03h	fs_rmdir	Remove an empty directory, SI = name, CF on err
04h	fs_unlink	Delete a file, SI = filename, CF on err
10h	io_close	Close fd, BX = fd, CF on error
11h	io_fstat	Get file status, BX = fd; AL = mode, CX:DX = size
12h	io_ioctl	Device control, BX = fd, AL = cmd, args in other regs per (fd_type, cmd); CF on err
13h	io_open	Open file, SI = filename, AL = flags, DL = mode; AX = fd, CF on err
14h	io_read	Read from fd, BX = fd, DI = buf, CX = count; AX = bytes, CF on err
15h	io_write	Write to fd, BX = fd, SI = buf, CX = count; AX = bytes, CF on err
20h	net_mac	Read cached MAC, DI = 6-byte buffer, CF if no NIC
21h	net_open	Open socket, AL = type (SOCK_RAW=0, SOCK_DGRAM=1), DL = protocol (IPPROTO_UDP=17, IPPROTO_ICMP=1; 0 for raw); AX = fd, CF if no NIC or table full
22h	net_recvfrom	Recv datagram via fd (UDP or ICMP): BX=fd, DI=buf, CX=len, DX=port (UDP) or ignored (ICMP); AX=bytes (0=none), CF err
23h	net_sendto	Send datagram via fd: BX=fd, SI=buf, CX=len, DI=IP; UDP also uses DX=src port, BP=dst port (ignored for ICMP); AX=bytes, CF err
30h	rtc_datetime	Get wall-clock time, DX:AX = unsigned seconds since 1970-01-01 UTC
31h	rtc_millis	Get milliseconds since boot, DX:AX = ms
32h	rtc_sleep	Busy-wait for CX milliseconds
33h	rtc_uptime	Get uptime in seconds, AX = elapsed seconds
F0h	sys_exec	Execute program, SI = filename, CF on error
F1h	sys_exit	Reload and return to shell
F2h	sys_reboot	Reboot
F3h	sys_shutdown	Shutdown