No rest for the simulated
SkoolKit 8.10 has been released. To get a copy, please head over to the download page, the Python Package Index, or GitHub.
As the title suggests, this release of SkoolKit is (again) almost entirely
about Z80 instruction set simulation. And to rub salt in the wounds of those
who still have no interest in the subject, it’s specifically about Z80
instruction set simulation in the service of LOADing tapes. To my recollection,
never has a single SkoolKit command received so much attention over a sequence
of releases as tap2sna.py has since 8.7 came out in October last year. So, to
the fans of tap2sna.py that are still reading: strap in.
First up is the finish-tape simulated LOAD configuration parameter, which
(when set to 1) forces tap2sna.py to play the tape to the end before stopping
the simulation at the given start address. This is particularly useful for
custom loaders that hit the start address more than once during the loading
process, and also for stopping purely ROM-based loaders at $053F (SA/LD-RET)
after the last block on the tape has loaded.
Next is the contended-in configuration parameter, which (when set to 1) makes
tap2sna.py interpret ‘IN A,($FE)’ instructions in the address range
$4000-$7FFF (i.e. contended memory on a standard 48K Spectrum) as reading the
tape. Lest you think this couldn’t possibly be useful, it’s actually required
by such games as Fly Swatter,
Removal Deluxe and
Sapper, all of which have custom
loading routines located in the aforementioned address range.
After that, there are 32 new tape-sampling loop accelerators in this release,
brought in to accompany the original 11. And although the casual user will
rarely need to think about them, if you are curious which accelerators (if any)
a game uses, you can now set the accelerator simulated LOAD configuration
parameter to list, and tap2sna.py will do just that:
$ tap2sna.py --sim-load -c accelerator=list GYROSCP2.TZX gyroscope2.z80
Program: GYROSC.II
Fast loading data block: 23755,1250
Data (602 bytes)
Data (46414 bytes)
Tape finished
Simulation stopped (end of tape): PC=64809
Accelerators: rom: 12857; speedlock: 113290; bleepload: 632000; misses: 25/62
Writing gyroscope2.z80
The Accelerators line here shows that a rom-style tape-sampling loop was
entered 12857 times, a speedlock-style loop 113290 times, and a
bleepload-style loop 632000 times. In addition, the tape-sampling loop
detectors, which are triggered by ‘INC B’ and ‘DEC B’ instructions, counted 25
misses for ‘INC B’ (i.e. 25 instances of ‘INC B’ not inside a recognised
tape-sampling loop) and 62 misses for ‘DEC B’.
For those even more curious about custom loaders, the format of the trace log
file produced by tap2sna.py during a simulated LOAD can now be defined via
the TraceLine and TraceOperand configuration parameters. In addition to the
current address and instruction, you can log the current value of any register,
and also the current time (in T-states) as recorded by the simulator’s internal
clock. In conjunction with the new --tape-analysis option of tap2sna.py,
which provides an analysis (including timestamps) of a tape’s tones, pulse
sequences and data blocks, this enables you to figure out what’s being loaded
and where at any point in the loading routine. If that’s your kind of thing.
But if all of this so far seems like too much information, and all you want is
for --sim-load to just work for a particular tape, you could do worse than
consult the t2sfiles repository. It
contains ready-made ‘t2s’ (tap2sna.py argument) files for thousands of games,
with appropriate start addresses already figured out, and appropriate
accelerators already specified.
And on that note, I shall direct any readers who want even more information on
the goodies (simulation-related and otherwise) inside SkoolKit 8.10 to the
changelog. When you’re done
there, please download a copy of 8.10, and perhaps a copy of the
t2sfiles repository, and give
--sim-load a good workout. For real this time.
