I’ve just been playing with the save game option in RetroPie / RetroArch and this is what I have so far.

There are 2 methods of saving games. One is using the “in game” save files, in the same way as you would if you were using the original hardware.
The second method is to take a “snapshot” using the emulator itself, in this case RetroArch.

I have found that when playing the games (that are emulated by RetroArch), when you make an “in game” save, i.e. in Zelda on the SNES, the *.srm file will automatically save correctly in the rom folder. The folder can be specified, but the rom folder is default. This will only work correctly if the permissions are fine, which they are by defaut (the pi user must be able to write files in the relevant rom folder).

This means the next time you run the game, it will happily load the *.srm file and allow you to access your “in game” saves as normal.

In addition to the game saving the *.srm file, you can set it to keep saving this every x seconds using the retroarch.cfg file and this line:
autosave_interval =

Whilst that wont make any difference to where the save happens in the game, it just ensures that it is regularly saved to the SD card – although I’m not sure it has a lot of value as I’m not using it and its working fine (although this may in part be due to me always making sure I exit the emulator cleanly, going back to Emulation Station).

As I mention, the *.srm save works fine out the box for me, no config changes needed.
You can verify by searching for *.srm files on the SD card.

The second method of saving games is using “Save States”, the game itself doesnt have any concept of this, but the emulator (RetroArch) can use them.

This is very useful for games that dont have a built in save facility, as it allows you to store the position you were in when you stop playing. This is again controlled in the retroarch.cfg file

Here are the settings to auto save and/or auto load snapshots.

# Automatically saves a savestate at the end of RetroArch lifetime.
# The path is $SRAM_PATH.auto.
# RetroArch will automatically load any savestate with this path on startup if 
savestate_auto_load is set.
# savestate_auto_save = false
# savestate_auto_load = true

You can save and load these with the keyboard using the settings

# Saves state.
# input_save_state = f2
# Loads state.
# input_load_state = f4

or map them to your joypad (in the controller config) using hotkeys: for example
input_enable_hotkey_btn = 8
input_save_state_btn = 5
input_load_state_btn = 4

If anyone is interested I could put a video together showing how this works.