Steven Seagal's Atari ST Web Site

Steem

page 1 - page 2 - page 3 - page 4 - page 5

 

 

"Of mice and computers"

  Third screen of brags for v3.7.  
     
 

HD6301 emulation

 
 


The Atari mouse was durable if you didn't need buttons

 
     
  In 6301/ACIA mode the mouse will be quicker and move less erratically than before (especially in higher resolutions it was painful) while still being precise at lower speeds. Definitely less of a hack now and better than some other emulators.  
     
  It's not easy to get right because at hardware level the mouse movement translates to a '0011' bit sequence rotating, at the right speed. In Steem the conversion happens at VBL level (50hz generally).  
     
  This is also an indication that our 6301 and ACIA timings are not so bad after all.  
     
     
 

Arkanoid

 
  So is it enough for a game like Arkanoid? Still not sure.  
     
 

 
 

Some levels are tough, what fool designed this madness?

 
     
   
  Still beatable  
     
 

Joystick jump button

 
 

 
  A terrible shortcoming of the Atari ST was one-button only joysticks. On arcade machines, there were generally 2 buttons, so one was used for fire, another for jump, for example. On computer conversions, or on computer games in general, you needed to push the joystick forward to jump.

In v3.7, Steem allows you to map an alternative button to 'up', while also keeping the joystick movement, so now you can play a platformer any way you like.

Note: on the screenshot, axes are reversed so the buttons of the Speedlink are on the side, it's peculiar to this joystick.

 
     
     
 

High Res Overscan

 
  Preliminary support for overscan techniques in high resolution (monochrome screen).

Yes! You may abuse the GLUE when you have a monochrome screen too.
It's the same idea: changing shift mode when the GLUE is about to make
decisions.

 
  Monoscreen by Dead Braincells:  
 

 
 

First nothing in the borders

 
     
 

 
 

It's hard but see, overscan!

Very trashy effect for the moment. The problem, in Steem, is that emulation concepts may collide with the video rendering system, which was written in Intel assembly, and which I can't properly mod for now.

 
     
     
 

My Socks are Weapons

 
 

 
  Another protected demo now running in the Legacy of Steem, fans get their socks knocked off again!
The protection of this demo is rather vicious for us emulator maintainers. It sets the ST in highres, then uses the video counter in the middle of its trace decoding routine.
Other trace protection routines set the ST in highres too, and for a long time, but without reading the counter (Transbeauce 2, etc.)
 
 
     
 

Halt

 
 

 
  No more endless reset on "crash and burn" (technically: supervisor stack too small to save exception parameters), just stopping is clearer. Notice the mention in the status bar. If you press play, it stops at once. You must do a cold reset to restart Steem.

Due to improvements in Steem those cases get rarer. Here's the bad image of Fuzion 78 that should always crash anyway.

 
     
 

Relapse

 
  Alas, I relapsed into my hacking habits...  
     
  This is Grafix Sound II plasma first without then with the hack:  
 

 
     
 

 
 

What will it break? :)

 
     
 

Awesome 04 STF

 
 

 
  Being a ruthless plasma fan, I also fixed this menu in STF mode. 
In fact the fix is also a hack as this aspect of emulation looks pretty awesome to emulate: we should have an up-to-date data bus at each moment (that is, at the level of microcodes).
It looked very bad in v3.6 but it wasn't correct in previous versions either. Note, it always was fine in STE mode.
 
     
 

PRG and TOS files support

 
 

 
  In the new version of Steem, standalone Atari PRG and TOS executable files will be treated as disk images. Just launch it and it starts.  
  Please read "note.txt" in the new PRG folder for instructions, you must set something up (easy).  
  If it crashes, likeliest explanation is that other files are necessary beside the PRG or TOS, or maybe the program doesn't like the hard drive, etc.  
  So there are limitations but the feature will prove useful, for instance for all those "cracktros" available as a single PRG file.  
     
 

Disk manager

 
  Double click on nothing goes up one level in the path.  
  Right click on the icon toggles hard disk on/off (with mention in the status bar).  
     
     
 

Sound emulation

 
 

 
     
  First, all options related to sound, including drive sound and keyboard click, have been moved to the sound page. This was made possible thanks to some rearrangement of the controls, which is quite easy to do in the structure left by Steem authors (should have thought about it before).  
     
 

 
     
 

Second, the situation for sound output type (filters) has been made clearer.

The different choices are presented as various filters.

'Coaxial' and 'SCART' are the connections between the ST and respectively a
TV or a monitor. Notice the addition of a Hatari filter.

 
     
 

 
 

This is legend, not the Amiga 8bit samples!

 
     
 

Third, when option Sampled YM-2149 is checked, emulation of the P.S.G. sound chip will use the table provided by ljbk of atari-forum. This table contains real output values of "fixed volume" as measured on an Atari STF.

The table was already used in previous versions, but only when option 'Samples' was checked (so this option isn't necessary anymore) and Steem reckoned that samples are being played.

The sound is now much louder on chip tunes, even distorted, but that's correct emulation. A nice example is the B.I.G. Demo opening tune 'Ace 2'. If you don't like that screaming distortion, you may still uncheck the option (Steem "original").

 

 
  Technical notes  
     
  Hatari had it (more or less) right first this time. In Steem, you had to change somewhat the way sound is rendered before you could use the table for all emulation. Sound was directly rendered for each channel (A-C) in real time so that you had no value to use in the look-up table. Instead of that, when the option is checked, Steem now stores the volumes in digital form (4bit, 5bit) in the sound buffer and delays rendering. Then at each frame, the buffer is translated sample by sample.

When the program uses the envelope (5bit), Steem interpolates a value using the 16x16x16 table (4bit), but without pre-computing a larger 32x32x32 table.

The table is loaded in memory and removed each time you change the option.

 
     
 

SSE Options

 
 

 

 
  Other options have been moved too. ST model and wake-up state to Machine.  
     
 

 
     
  Display size to... Display. Also two new options appear, to better control window resizing.  
     
 

 
     
  And this is the new SSE option page.  
     
 

 
  Low-level emulation of the IKBD chip (keyboard, mouse, joysticks) requires improvements in ACIA emulation. Precise ACIA emulation requires improvements in the E-clock (a signal of the MC68000 CPU) emulation. They're tied together and are regrouped as "C1" on the option page. When checked, C1 also appears in the status bar. C stands for "chipset".

There's also a "C2" option, for "chipset 2", but for the moment it only concerns the MFP.

Those abbreviations were chosen to limit the length of the status info string.

Both option C2 and Fine tune CPU clock are presented on brag page 5.

 
     
 

B.I.G. Demo

 
 

 
  A mysterious glitch in emulation of the 2nd screen has finally been fixed in v3.7.
There was a bad raster in one of the bubbles.
The reason for that was that even on "-2 lines" Steem would fetch and compute and
display a 160 bytes line (instead of 158), including the last 2 bytes, that are meant
for the next line. That was fishy...
This is one of my favourite ST screens so that's a big fix.
 
 
     
 

The Teller

 
 

 
  The trace protection of this game told me that my "general theory" of exception stack frame was missing some piece.

I thought there was an error, but Motorola microcodes tell us more about the JMP instruction: the PC doesn't change before the address error exception. Why should it after all, tell me?
There are 876,079 exceptions during the decoding, the current record as seen in Steem.

 
     
     

 

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