Precompiled Overlays???
Christof Eb.
Posts: 1,589
Hi,
as we are all running short of RAM sooner or later, I wanted to start some discussion about precompiled overlays. Idea is instead of holding everything in RAM all the time, have the machine quickly load a chunk of stuff from SD card. For example an editor or an assembler does not need to be in RAM all the time.
So far I have found one resource about this: https://www.forth.org/fd/FD-V05N1.pdf
Do you know other implementations? Ideas, comments, suggestions?
Christof
Comments
A RAM expansion is even faster than SD card for such a use. SD card can still be the file store but loading everything into extended RAM at power up will allow for much smoother runtime operation.
I presume Ada's game emulators are done alone these lines. She has mentioned it only functions as a ROM replacement - Which is similar nature to overlaying. This will be because when the content is read-only it can be reliably fetched in contiguous bursts and it doesn't really matter if only one byte is needed. The remainder can hang around or be tossed.
Writes are difficult because optimising for tiny writes is way different to contiguous bursts. So then that leads to having to do checks, which are always cumbersome.
Catalina supports overlays for both the Propeller 1 and Propeller 2. See the section Using Catapult with Overlay Files in the document Getting Started with Catapult and the examples in demos/catapult/over_p1.c (Propeller 1) or demos/catapult/over_p2.c (Propeller 2).
However, this seems to be broken the current release!
I'll find out why and fix.
Ross.