Recently I tried to implement the ram expansion for the Apple II+ but failed again. The test suite didn’t recognize the additional ram or the additional memory access interfered with the disc access which lays in the sdram as well.
A little disappointed I was in need of a simple new project for my little free time. The vic20 was the obvious choice as it has low demand on memory and should be easy to port. But I was wrong.
The first difficulty was to find the right sources. Unfortunately there were no sources on the fpgaarcade site where it derives from. An Internet search revealed several places with several different implementations of the same original sources.
I started with the Papilio port but didn’t succeed. I got a screen output but only with a lot of “@”s.
Even though the sources were almost identically I got more success with the de2 sources. I used BRAM instead of SRAM and the vic20 on the MiST was alive:
But there’s still a lot do to to make it usable. The refresh rate is a little odd and needs a little tuning.
An internal test cartridge and one uploaded via the MiST osd didn’t start.
Due to this the sound output isn’t tested. The vic20 is only unexpanded and needs some memory expansions.
And finally the boot time is rather long and I dunno what’s doing there (testing ram?).
Fortunately I found some resources on the net which might help me to got those topics done:
The sources can be found here: