Re: RND function on B series vs C64/C128

Am Sonntag, 19. Februar 2023, 16:39:11 CET schrieb Micah Bly:
> I’m working on a documentation project for the CBM II series.
> 
> In comparing the descriptions of RND() for C64, C128, and B series, and in
> some light testing, I think the function may behave differently. Before I
> write that down, I wanted to check if that made sense. I could just be
> misinterpreting what I’m seeing.
> 
> C128 system guide says X in RND(X) can be 0 for clock-based number, negative
> to pick a new see, and positive to use a random number from the RNG (not
> from clock).  Page 325. C64 wiki describes the same behavior as C128 system
> guide, in more detail, with a sample program to show difference between
> RND(0) and RND(pos). https://www.c64-wiki.com/wiki/RND
> “CBM 700 Reference Guide” (the thing CBM UK wrote that Protecto distributed)
> says only this: =====
> 
> expression < 0
> 
> The algorithm uses the expression number to calculate the random number
> ("seed").
> 
> expression >= 0
> 
> The algorithm uses the last previously formed random number to calculate the
> new random number ("series").
> 
> =====
> 
> I ran the test program from the 64 wiki on the B128 (vice), and I can’t see
> a difference really. Certainly not the pattern you see in the pic on c64
> wiki. Timer is very different on B series… is it possible they just decided
> not to offer that option?

you could look up where the jiffy counter is, and put a breakpoint on read on 
it, like

watch load $123

perhaps do the same for CIA timers and some other possible sources, then do a 
?RND(0) and see if it triggers.

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