One hint that it's really not that easy could have been the lengths tokra and I went through to expand the graphics capabilities beyond the 'standard' 160x192 pixels bitmap of MINIGRAFIK. As the VIC chip can only use $0000 .. $03FF and $1000 .. $1FFF (5K in total) of an unmodded VIC-20, all graphics data need be sent through this needle eye. That's why the 6502 has to shuffle the graphics data from expansion memory into the internal RAM, so VIC can display it - synchronous to the raster beam. This emulated DMA uses up nearly 100% of the CPU time.
Contrary to this, the VFLI mod provides the 208x256 bitmap mode (PAL) essentially for free - the MAXIGRAFIK equivalent is done with just 2 NMIs per frame. To switch the three global colour registers and the colour RAM bank on each displayed raster then again eats up 256 of the 312 rasters, but that means there's still 20% of CPU available to the main program.
BTT: a monitor with a direct assembler would also be a nice tool in the $9800 to $9FFF range. (Edit: see here
)The whole range can be written to (in some parts writes are very slow though), however the registers are strewn across all I/O 3 at $9x00 and $9x80 - one of them triggers a reset, the others change BLK5 between RAM and two different ROM chips - so surprises are guaranteed.tokra wrote:But are the full 2K theoretically available to use fully with the MegaCart as "pseudo-ROM" using tlr's injection tool?
Any program or game which requires me to do this, because it wrote all over the Mega-Cart NVRAM won't get a second chance to run on my VIC-20.Possibly the MegaCart would need to be restored through the Service Menu to its factory settings or stored preferences afterwards.
