Although it’s not easy to pin down, I have read evidence that the Vice core should support the Vic-20 in addition to the C64. The problem? Getting the emulator in its Vic-20 mode. It defaults to C64, and loading a Vic-20-intended tape file doesn’t change that, because the tape format was 100% cross-compatible between the Vic-20 and the C64.
Since I’m trying to accomplish this from the command line, that’s what I’m after: The working syntax. So, quick and dumb question. Thanks in advance.
For be short, you cannot in the actual state .
Vice core ( x64/X64SC/X64DTV/X64SCPU/X128/XCBM2/XCM5X0/XPET/XPLUS4/XVIC…) need an makefile to be abble to be built .
this was done with the earlier implementation (look at makefile.CORE for 2.4 here https://github.com/r-type/vice-libretro )
But for now , in vice 3.0 , we only have done X64/X64SC/X128 makefile , and we have only recipe for X64/X128 ( i think). As no one asked for it , I never gone further.
I will look at to add VIC20 makefile at my own and if everything is fine push it on github.
@r-type I Had a quick look at “porting” the xpet and xplus4 but since I’m no real programmer, but I’m failing spectacular 
Any pointers?
You can look at here https://github.com/libretro/vice-libretro/blob/master/Makefile.xvic
basically you have to add files needed for the core to the makefile (and remove the unneeded that cause issue). build the official vice can help for this task. then find the good value for the screen size… add/hide option for the core …
I think I’ll leave transposing the make file to “professionals”
BTW someone need to do a recipe on libretro super.