Improve Compatibility with Radastan Mode
Lores mode on the Next operates at 128x96x8 resolution using the two Timex display files to form a chunky picture. A radastan mode was added for compatibility with the uno. This is 128x96x4 and allows a screen to fit into one display file.
Finding information about radastan mode was quite a bit harder a few years ago than it is now so some guesswork was applied. Something that was not realized is that radastan mode automatically implies use of the ula+ palette on the uno, which makes sense as there is no other easy way to map 4-bit pixels to colours without it. On the Next, there is a bigger palette so lores mode does not need to nor should it imply ula+ in normal operation.
So as radastan is there mainly for compatibility with the uno, look into increasing compatibility with the uno. This includes:
- implementing the same register accesses to enable
- implying ula+ use
- implementing scrolling via base address offset
https://www.zxuno.com/wiki/index.php/ZX_Spectrum#Nuevos_registros_E.2FS_para_control_de_ZX-Uno
https://uto.speccy.org/zxunofaq_en.html
https://spectrumcomputing.co.uk/forums/viewtopic.php?p=77766#p77766
There are several things about radastan as implemented on the uno that might not make sense on the Next but this is still worth looking into.