Added cartridge emulation to C64

[tcdev]

Targets with flash memory now support cartridge emulation for C64.

More details to follow whn I check in to SVN...

[tcdev]

I've updated the repository with DE1 & DE2 builds of C64.

The switches have the following functions:

9..4 flash (16KB) cartridge bank == A(19..14) of the flash.
3 exrom (0=de-asserted)
2 game (0=de-asserted)
1..0 C1541 device address (00=8)

EDIT: to explain a little better...

You can load up to 32x 8/16KB cartridges into flash and select which image is active via the dipswitches.
Cartridges, whether 8KB or 16KB, must be programmed on 16KB boundaries in flash.
Note: I've found that sometimes changing cartridges requires re-programming the FPGA! A reset (KEY0) is not sufficient!?!

I've tested Lode Runner, Pacman, Donkey Kong, Galaxian and Moon Patrol cartridges. They all seem to work OK. v0.27 also appears to have fixed the graphics glitches.

However, there may be a problem with the SID output. I need to look into this a little more closely...