I have a question: how to get more free space in DoS?
I want to enlarge the rooms of DoS, but it shows "can't find any free space."
Than I use the "Add overlay", and open _dsvedit_freespace and add "030a5700 0001f600 /ftc/overlay9_41" in the end.
But it still "can't find any free space."
030a5700 is a address, and after this address there are all 00. I think it's a good site to put free space.
First of all, I don't know where you got the address 030a5700 from, but it's definitely not an address in main RAM. I looked it up and apparently addresses in the 03000000 range are in "Shared WRAM" - I don't know what that is but you can't use it for free space.
Second of all, the first number you put in _dsvedit_freespace is not supposed to be an address, it's supposed to be an offset within the file (/ftc/overlay9_41). For example, 00000000 if you want the free space to start at the start of the file. 00000100 if you want the free space to start 0x100 bytes into the file. If you want more details about how this works you can read the "Adding a free space overlay" section of the readme: https://github.com/LagoLunatic/DSVEdit#adding-a-free-space-overlay
If you want the entirety of overlay 41 in the USA version of DoS to be considered free space, you should put this in _dsvedit_freespace:
00000000 00016000 /ftc/overlay9_41
If you're using the JP version of DoS it would be:
00000000 00010000 /ftc/overlay9_41
But be careful, if you do that you can never apply any ASM patches that use free space, because the ASM patch would overwrite the other data that DSVEdit put there and corrupt things. (For examples out of the asm patches I've written, "dos_magical_ticket.asm", "dos_add_hole_to_map_doors.asm", "dos_prevent_multiple_cutscenes_in_first_room.asm", etc.)
In case you ever decide to use an ASM patch that uses free space, you may want to set aside some space at the start for that, like this (USA version of DoS):
00001000 00015000 /ftc/overlay9_41
In this example, I didn't mark the first 0x1000 bytes inside overlay 41 as free space. That means you have 0x1000 bytes for any ASM patches you might want to use. The amount of free space you can use for other things besides ASM (such as entities and layers) is 0x15000 bytes here, whereas it was 0x16000 bytes in the first example.