https://github.com/AleffCorrea/DiscMakerI just did a batch file that merges all the binary data you want (ie tile graphics, audio samples, etc.) into a single ISO file which is CDROM compliant (it automatically pads the file to 150 frames).
Not only it pads the whole file, but also individual binaries so they are 2048 byte (frame) aligned. This, of course, is done to not overcomplicate loading data from the disc to VRAM/SYSCARD RAM and to make the padding process for your data automatic. This also spits out an .asm file containing constant defines for what the sector index of your inputted data files are, and how many bytes and sectors it occupies on the disc.
The only downside to this batch file is that you need to run this first before compiling your game (because of the index asm file), and then to copy it manually with copy /b (or with this tool itself if you don't mind to see the index asm file getting overwritten with nonsense, but since you won't need it after compiling your overlays it might not be an issue for you). Also,
this doesn't add the sector 0 IPL file to the ISO, you're expected to add it yourself, just like the game overlays. The first parameter of the batch file is a sector offset so you have the indexes from the asm file properly aligned.
Anyway, no one will use this since everyone uses HuC and the isolink thingy, but I thought I'd share anyway. Hope it's going to be useful to someone aside from myself.