ds:si packet address int 13h ah=42h

[Mikemk]

Sorry if the answer is obvious, but how would one put the address of the ds:si packet in ds:si using nasm?

[evoex]

Read up on segmentation and real-mode on the wiki:
http://wiki.osdev.org/Segmentation
http://wiki.osdev.org/Real_Mode

Hope that helps

[Mikemk]

http://wiki.osdev.org/Segmentation

Thanks, quite helpful

[Mikemk]

Code: Select all

1  mov [si], DWORD [packet]
2  mov es:[bx], 0x500

line 1 produces "error: operation size not specified"
line 2 produces "error: invalid combination of opcode and operands"

What am I doing wrong?

[Mikemk]

nm, I figured it out

[neon]

nm, I figured it out

Im not convinced you have.... mov [es:bx], ax stores ax into the location at es:bx; it does not set es nor bx. If you want to set ds and si to contain the address of the packet, you need to know real mode addressing:

Code: Select all

mov ax, 0x7c0 ; ds:si -> 0x7c0:packet
mov ds, ax
mov si, packet