Atari 5200 PAL Prototypes

[Tempest]

I want to take a closer look at the two 5200 prototypes I dumped years ago that were labeled PAL.  However since I'm not really familiar with PAL timings and colors and whatnot being from an NTSC country, I need some help in this regard.  I found that I can put the Atari800 emulator into PAL more for the 5200 and do some quick testing, but I'm not really sure what to look for.  As far as I can tell the Missile Command PAL proto plays with its screen somewhat compressed in PAL mode vs the released version when put into PAL mode (the colors look the same) but Star Raiders looks the same (I think it is the same as the released version).  It's hard to do a binary compare because all 5200 carts seem to be overdumped to 32K for some reason.

 

Can someone please take a look at these roms and see if there's anything I'm missing, especially with the Missile Command one?

 

 

Missile Command 4-4-82 (PAL).bin Star Raiders 2-23-83 (PAL).bin

[Kr0tki]

On 7/11/2021 at 3:30 PM, Tempest said:

It's hard to do a binary compare because all 5200 carts seem to be overdumped to 32K for some reason.

I would recommend you to download the No-Intro Atari 5200 ROM set - it contains the ROMS in their pristine, non-overdumped form (except for Zaxxon, which should be 16KB, but the two 16KB copies within the existing 32KB ROM dump differ on two bytes, indicating that it might be a bad dump; and several 12KB, 20KB and 24KB ROMs that need to be padded to 16KB/32KB anyway because emulators do not support these ROM sizes).

 

Investigating PAL vs. NTSC differences requires proper setting up of the emulator - some "modern" features such as accurate emulation of colour palette and aspect ratio correction need to be disabled, as they tend to hide whatever the differences are implemented in software. I'm gonna help you out on this later today.

Edited July 13, 2021 by Kr0tki

[Tempest]

39 minutes ago, Kr0tki said:

Investigating PAL vs. NTSC differences requires proper setting up of the emulator - some "modern" features such as accurate emulation of colour palette and aspect ratio correction need to be disabled, as they tend to hide whatever the differences are implemented in software. I'm gonna help you out on this later today.

I'd appreciate that

[Kr0tki]

Oookay, I think I've skewed the definition of "later today" far enough.

 

So, modern emulators (talking about Altirra and Atari800 here) accurately emulate NTSC/PAL palette differences and NTSC/PAL aspect ratio differences. But that means, when a game implements its own palette- or aspect ratio adjustment, it tends to be difficult to notice because of these emulator features! So for the purpose of investigating differences in a game's behaviour it's best to disable these features.

 

As an example, GATO title screen in NTSC and PAL. GATO is known to not make any system-specific adjustments by software, so the differences in colours and aspect ratio are purely the result of the emulator being accurate.

 

In Atari800, to disable NTSC/PAL aspect ratio correction:

1. Go to "Display settings -> Video mode settings".

2. Ensure that "Host display aspect ratio" is set to your monitor's aspect ratio (typically 16:9).

3. Ensure that "Hardware acceleration" is set to "yes".

4. Ensure that "Stretch image" is set to "fit screen - full" and "Fit screen method" is set to "fit both".

5. Set "Image aspect ratio" to "square pixels".

6. Set "Vertical view area" to "full overscan".

 

In Atari800 we also need to disable artifacting, because it interferes with aspect ratio settings.

1. In "System settings" switch "Video system" to NTSC.

2. In "Display settings" set "Video artifacts" to "off".

3. In "System settings" switch "Video system" to PAL.

4. In "Display settings" set "Video artifacts" to "off".

 

To disable NTSC/PAL palette correction, we will apply the NTSC palette to the PAL TV system. In Atari800:

1. In "System settings" switch "Video system" to NTSC.

2. In "Display settings" select "Save current palette". (The option in on the "2nd page" of the menu, just go all the way down in "Display settings" and then down once more.)

3. Enter path to file of your choice, e.g. "C:\atari\ntsc-palette" - the palette will be saved to a file.

4. In "System settings" switch "Video system" to PAL.

5. In "Display settings" select "External palette".

6. Navigate to the palette file created in step 3 and select it - the colours should immediately change.

 

Now it is way more convenient to notice if a game adjusts screen or colours between PAL and NTSC. As an example, the retail version of 5200 Missile Command in NTSC and PAL. It is immediately visible that when run in PAL, the game uses more screen vertically.

 

Another example, the retail version of 5200 Star Raiders with shields enabled, in NTSC and PAL. It is immediately visible that the game in PAL mode uses a different colour for the shields. It was done because the colour from the NTSC version would look green on real PAL machines. (And it would also look green in emulation, if you were to re-enable proper NTSC/PAL colour emulation in Display settings.)

 

As for the specific differences in the PAL prototypes of MC and SR: As you may know, most 2-port 5200s contain the newer version of the BIOS - and the only change introduced in that BIOS is regional locking for PAL cartridges. If a 2-port 5200 console was a PAL version, the BIOS would check if the inserted cartridge was a PAL version, and halt if it isn't. Specifically, the BIOS checks:

1. if the cartridge is diagnostic, i.e. contains $FF in $BFFD -> if it is, runs it.

2. if the cartridge contains a specific value in $BFE7 -> if it equals $15 or $30 or if its bit 1 is set, then the BIOS runs the cartridge; otherwise it halts.

 

Apparently Atari's intent was to lock US cartridges from being used in PAL 5200s. If you use the 2-port BIOS in the emulator, switch to PAL, and try to run any of the ROMs made by Atari, in most cases they won't run.

 

Now when it comes to PAL Missile Command and Star Raiders ROMs, they both have the value in $BFE7 set to $02 (MC) and #03 (SR) in order to pass this regional check. In fact, in the case of SR, the only difference between the NTSC and PAL versions is in the three bytes between $BFE5..$BFE7 - so we should not expect any differences in gameplay.

 

With PAL MC the ROM is different overall. The only gameplay difference I noticed is that the PAL proto does not adjust the screen area differently between NTSC and PAL - it uses the "NTSC height" in both TV systems, which is, to be frank, inexplicable.

Edited July 16, 2021 by Kr0tki

[Tempest]

So the PAL Star Raiders prototype has the value set so it passed the PAL/NSTC check in the 2 Port BIOS but the retail version doesn't?  And this would only happen on a PAL 5200 which doesn't exist?

 

As for the PAL MC proto, the reason the screen looks squashed on an NTSC display is because it's not setting the PAL height correctly?

[Kr0tki]

3 minutes ago, Tempest said:

So the PAL Star Raiders prototype has the value set so it passed the PAL/NSTC check in the 2 Port BIOS but the retail version doesn't?  And this would only happen on a PAL 5200 which doesn't exist?

Exactly.

3 minutes ago, Tempest said:

As for the PAL MC proto, the reason the screen looks squashed on an NTSC display is because it's not setting the PAL height correctly?

No - when you run either the retail MC or the PAL MC on an NTSC 5200, both will look the same. But if you run both on a non-existing PAL 5200, then the retail version will cover more vertical screen estate, while the PAL proto will look squashed.

Edited July 16, 2021 by Kr0tki

[Tempest]

5 minutes ago, Kr0tki said:

Exactly.

No - when you run either the retail MC or the PAL MC on an NTSC 5200, both will look the same. But if you run both on a non-existing PAL 5200, then the retail version will cover more vertical screen estate, while the PAL proto will look squashed.

Ah ok I've got it now.  I'll update my page.  Thanks for all these findings.

[Tempest]

BTW did you notice if MC played any slower than the NTSC version or was that just my imagination?

[Kr0tki]

You are right!

 

Typically, games run on PAL are slower that in NTSC, because the gameplay is synchronized with the screen refresh rate. This is not the case with the retail MC - it seems to be running roughly at the same speed in both NTSC and PAL. But the PAL proto seems to be synchronized with screen refresh rate! On an NTSC 5200 it will run at the same speed as the retail version, but on a PAL 5200 it is noticeably slower!

 

That just does not make sense. The retail version seems to be better-suited for PAL systems (both in the screen size and speed) than the PAL-specific one!

Edited July 16, 2021 by Kr0tki

[Tempest]

I'm also curious as to why the splash screen says copyright 1981

[Kr0tki]

Well, the 8-bit version was copyrighted 1981, and this one is based on the former, so that's one possible reason.

 

In any case,  I have binary-compared the PAL proto to both the 5200 and 8-bit retail versions, to see if the PAL proto is "close" to either of them, to determine "lineage", to no avail - there is a lot of changes in the layout between all three versions.

 

The 5200 shipped in October 1982, with MC as a launch title. The PAL proto is from April 4, presumably 1982. It seems that the PAL 5200 was being worked on way before the NTSC version shipped. So my presumption is that this PAL proto was created while MC was still in development, only for the purpose of testing region locking. That would explain why the PAL proto has less features than the retail version.