New answers tagged memory-layout
7
What was at 0x0500-0x7bff that caused this convention?
Nothing. There is no hard (-ware related) reason. And while loading an OS at top or bottom of memory is more of a philosophical question, it's one the OS to be loaded needs to decide for itself - nothing the BIOS should imply.
So lets better look at what are the requirements for a boot location adding ...
10
As the least amount of memory needed to boot from floppy was 32 kilobytes, the first sector of the floppy, the FAT volume boot record, is loaded to just before the 32 kilobyte end of memory. However, it is loaded to 1 kilobyte before the end of memory, but the sector is only 512 bytes, so it could fit two sectors, or the remaining 512 bytes can be used for ...
3
The header file that is used in your linked source code directs WLA to compile for a ROM using the LOROM map and the first 32K of ROM are mapped into bank 0 at offsets $8000-$FFFF. So your (mapped) code starts at offset $8000, not 0.
As for the VBlank label: the header expects an NMI routine at that label, so your code must define an interrupt routine for ...
1
Just to add to the other answers - a somewhat odd solution, but doable for simple (but longish) "drawing" programs such as this, is to use Wozniak's old "Integer BASIC" (aka "Apple BASIC") instead of the more common (Microsoft-BASIC derived) "Applesoft BASIC". You do that by saying "INT" at the prompt after ...
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