From: Ullrich von Bassewitz (uz_at_musoftware.de)
Date: 2002-12-08 11:06:40
Hi!
On Sun, Dec 08, 2002 at 01:10:30AM +0100, Maciej Witkowiak wrote:
> In fact, I already did. It just needs testing and maybe tuning. Perhaps you
> will help me to decide how to deal with VDC. Due to memory layout of VDC
> there are only 16 free pages on a 16k VDC because I don't want to make memory
> driver and VDC screen usage exclusive things. However VDC is also accessible
> in C64 but needs initialization from user, not the system. This is why I think
> that in C64 mode whole memory should be always available because the user
> would have to decide where to put screen map, colors etc. anyway.
With the other drivers, I've decided against automatic resource allocation,
because it is too much overhead, and often error prone. The c64-ram.emd driver
collides with the c64-hi.tgi tgi driver, because both use the memory below the
kernal RAM and I/O area. This is something, a user has to know. Similar, the
REU driver just checks the SIZE bit and does no tests for the size of the
installed memory, because I think the overhead is not worth it, and the test
may destroy existing data. It is easier to ask the user if his REU has more
than 256KB and use page numbers beyond what em_pagecount() returns if this is
true. The GeoRAM drivers do not test for the hardware, if the user wants
automatic detection, he is on his own. The reason for all this is to keep the
driver design simple, which is a big advantage.
So with the VDC driver, I think it would be best if the decision can be left
up to the user/programmer. An example would be: If the 80 column mode is in
effect, the programmer cannot use the last xxx (or first xxx) memory pages,
regardless of what em_pagecount returns. Things like this have to go into the
documentation, of course. Letting the user decide does also mean that people
not using any advanced features will not have to pay for it.
Regards
Uz
--
Ullrich von Bassewitz uz_at_musoftware.de
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