introduce SHADOW_RAM2
add support for SHADOW_RAM2 segment
introduce SHADOW_RAM2
remove __RESERVED_MEMORY__: not supported on atarixl
Default atatixl.cfg file now leaves the character generator at $E000.
This reduces the potential to flicker, but creates two separate
memory areas in the high memory.
For applications which require a large continuous memory space in
high memory, atarixl-largehimem.cfg is provided. With high IRQ
activity or DL interrupt there might be flicker.
Get rid of SAVEAREA segment: fold it into LOWDATA.