How to make 8Mbit game work on 32Mbit eprom

I have trouble with getting my 8Mbit game burned on a 32Mbit eprom to work when placing it inside my donor cart (SHVC-1A3M-30).

Im using a 32Mbit eprom (MBM29F033C) mounted on a type-III adapter (TSOP40 to Dip36) from buyicnow.com, and the rom that is burned to the eprom is an 8Mbit rom. The rest of the eprom is empty, i.e. no padding/mirroring have been used, although I now have realised that I should have done so.

Since I don't have any programmer or such, I wonder if there is any way of fixing my issue? I have read that the higher adress lines can be grounded, but I don fully understand that concept. Which of the pins should be grounded in my case?

You can only ground A21 and A20 IF (big emphasis on IF) they are not connected to the snes buss. IF A20 and A21 are not connected to the cart lines, then pulling those 2 lines to ground will hard-enable the first 8mbits. But I have burned 8mbit games before on big roms and it wasn't a problem. It depends on the game I think. Super Bonk was this way -- even though Super Bonk is 1.5mbytes, I had to mirror it to get it to work. What game are you trying to make?

ROM images that aren't power of two (.75 MB, 1.25 MB, 1.5 MB, 2.5 MB, 3 MB) will need to be mirrored up to a power of two. Mega Man X is another game that depends on this. But after it's mirrored up to a power of two, you can get away with tying unused high address lines to ground.

Thank you for your input! The first thing that comes to my mind is that the rom should always be mirrored until it fills out the whole eprom. Would that be a way to totally avoid the situation I am currently facing?

Mirroring to a power of 2 and then mirroring to the whole EPROM should also work. It can just be slower at times, especially with a slow EPROM programmer.

How should this mirroring be done? For example with a 3MB rom to a 4MB chip, how should it be done?

BR

3 MiB is the sum of two powers of 2. So cut at the next smaller power of 2, then double up the smaller one until it's the larger one. This means cut at 2 MiB, then double the 1 MiB part to 2 MiB.