[Coco] BASIC program crashing Xroar emulator?

[William Astle]

On 2025-02-27 10:51, Allen Huffman wrote:
>> On Feb 27, 2025, at 11:44 AM, William Astle via Coco <coco at maltedmedia.com> wrote:
>>
>> The only solution as far as I can tell is do no output on the 40/80 column screen or clear less string space.
> 
> Do we (you :) know what the max amount of string space you can clear is? I will check Unravelled, as I expect they discuss this somewhere.

It's not that straight forward and unravelled doesn't mention it. I only 
know because I tripped on it hard back in "the day" and it left me 
scratching my head for quite a while.

Basically, the stack has to stay above $4000 (the screen gets mapped in 
the $2000 to $3FFF range) so that would probably put the absolute limit 
somewhere just under 16K (16384). You'd want 200 bytes or so room for 
the stack so 16000 would be a nice round number. On the other hand, if 
you reserve any memory with the second parameter for CLEAR, that number 
goes down.

Perversely, if you could get the stack to be *below* $2000, it would 
also not crash, but that means a very small program with no PMODE 
graphics, probably.

The size of scalar variables, arrays, or program text doesn't actually 
matter for this calculation because the screen is not mapped in except 
when doing I/O on the screen.