Hi Eric/Rugxulo,

Thanks for your input!

I did read a long time ago the power.txt that Mike wrote, but had 
forgotten it since. After looking again, I saw the note about INT28h. 
After a few tests, I see that it's actually the best way, since it works 
on DOSBox, DOSemu, and VirtualBox making them all running cool (ie. not 
at 100% cpu). So I added it to Zmiy, and made the default energy-saving 

I still haven't figured out any simple way of performing time polling 
with sub-55ms precision, so I will probably leave it as is (that's not a 
very big deal anyway). I'm suprised though, that there is well-known 
microsecond-grade sleep function provided by the BIOS (int15h AH=86h), 
but no sibling function to just retrieve a timer with such precision. 
The 'reprogramming the PIT' subject is interesting, but I fear I won't 
have enough time to really figure all the implications to do it right.

About VGA: Yes indeed, Zmiy requires a VGA display for 80x50. On EGA, it 
will initialize the screen into 80x43, which will make the game hardly 
playable. I am thinking about converting Zmiy to 80x43 instead, then 
adding some VGA-detection routing to force it into 80x43. Will probably 
do this in some future release.


On 07/31/2013 12:13 AM, Rugxulo wrote:
> Hi,
> On Mon, Jul 29, 2013 at 2:36 PM, Mateusz Viste <mate...@viste-family.net> 
> wrote:
>> I had a few minutes of free time lately and felt the inexplicable need
>> to write a Nibbles clone
>> I called it 'Zmiy'. It's written in C89, compiled with Turbo C, and, as
>> usual, released under GNU GPL 3
>>    http://sourceforge.net/projects/zmiy
> Good to know.
>> ---- Boring LONG tech stuff below // you might want to ignore this -----
>> During the development, I encountered an interesting problem: timing.
>> It's probably obvious stuff to most people here, but I actually never
>> really played with game-oriented timing in DOS. I implemented inside
>> zmyi 3 different timing mechanisms (configurable via command line).
> I've not written a lot of low-level code, so my understanding of such
> things is limited to what I can glean from online forums (i.e. not
> much).
> What is the full list of environments you're trying to run under? Just
> everything you can get your hands on?  :-)
> Apparently:  native DOS, VirtualBox, DOSEMU, DOSBox, NTVDM
>> The first (best so far) is checking the time in a loop (at 18,2Hz), and
>> performing an int15h AX=5305h at every iteration to notify APM about
>> available CPU.
>> The second is about calling the BIOS function int15h AH=86h.
>> The third one is about using the Turbo C 'delay' function (supposed to
>> provide a millisecond-grade sleep).
> So you want sufficiently smooth speed but also power savings (not hog cpu)?
>> I was also wondering about issuing HLT instructions, but it doesn't look
>> like a nice solution to me, since it would require to add some asm into
>> my C project, and it wouldn't work on many platforms (Windows...), and I
>> feel it's not the application's job to issue HLT, this should be taken
>> care of by APM, or the BIOS, or whatever.. But not the application.
> DOSBox has adjustable cycles (and core and frameskip). DOSEMU, I'm not
> sure exactly what it's called, but it has some hogging threshold
> setting in some tool somewhere. Other environments may let you cap
> your cpu use too (e.g. VirtualBox: System Processor, Execution Cap or
> perhaps Windows: Task Manager, Set Priority). But usually I just leave
> things as default (since lacking much reason to delve further).
>> Any suggestion about some neat (and simple, if possible) usleep()-like
>> mechanism that I could use? My int15h AH=86h method is sleeping very
>> nicely (with high resolution), but it makes the keyboard laggy, so I
>> wonder if it's the best path.. I've read a bit about reprogramming the
>> PIT, but it sounds a bit scary, and probably not allowed by Windows
>> anyway (I'd like to keep zmyi 8086-compatible, but still playable on
>> other platforms).
> I consider Windows almost a lost cause. XP at least somewhat works
> (barely), but outside of that (Vista, 7, 8) it's probably not (IMHO!)
> worth even trying.
> int 15h, 86h is limited under modern NT-based Windows, IIRC, something
> about not updating as frequently as you'd want. You'd have to check
> DJGPP libc sources, I forget the details:
> http://www.delorie.com/bin/cvsweb.cgi/djgpp/src/libc/pc_hw/timer/uclock.c?rev=1.5
> As for just not wasting cycles, you may? wish to try the equivalent of
> __dpmi_yield, which is basically just calling int 2Fh, 1680h. N.B. You
> must call this via int 31h, 300h in order to work properly under
> WinXP. And of course check to make sure the vector of int 2Fh isn't
> zero first (before testing for DPMI before actually calling this). Not
> supported by every DPMI environment but helpful to those that do. (I
> think even mTCP uses this nowadays, see POWER.TXT.)
> https://code.google.com/p/mtcp/
> And here's some more obligatory links:
> http://www.bttr-software.de/forum/board_entry.php?id=10006#p10397
> http://www.delorie.com/djgpp/doc/rbinter/id/33/15.html
> http://www.delorie.com/djgpp/doc/libc/libc_279.html
> http://www.delorie.com/djgpp/doc/rbinter/id/47/45.html
>> BTW, if you test Zmiy on DOSBox, you will notice that the palette is
>> wrong. I have no idea why - seems that DOSBox initializes a different
>> palette on 80x50 than what a real PC do.
> Just a silly question, if this is using 80x50, doesn't that mean it
> requires VGA? Do you test for that before using it? Just saying, not
> all 8086 machines had a VGA.   ;-)

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