Taito TC0690 IRQs

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NewRisingSun
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Taito TC0690 IRQs

Post by NewRisingSun » Mon Jan 07, 2019 10:48 am

Splitting from a discussion that came up in another unrelated thread ...

Mapper 48's IRQ is stated as being generated later than on the MMC3, but there is more: It seems impossible to get the IRQs to fire at the correct scanline in both The Jetsons: Cogswell's Caper's title screen and The Flintstones: The Rescue of Dino&Hoppy's status bar, either one will be off by one. The wiki page advises to XOR the latch value with FF to get the MMC3 equivalent value, which indicates that Taito's chip counts up, not down. When counting up, there is always the question of raising the IRQ when the counter reaches $FF (similar to the Namco 163's CPU Cycle counter) or when it wraps from $FF to $00. I noticed that Flintstones works well when raising the IRQ at counter $FF, while Jetsons works well when raising the IRQ at the time that the counter wraps (plus a delay of at least six CPU cycles, not four as the wiki states). This may be a coincidence, but it is the sort of thing that one would expect from a chip revision. If this hypothesis could be tested with the chips found in cartridges of both games, and confirmed, then a submapper could be allocated to indicate the IRQ counter behavior.

lidnariq
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Re: Taito TC0690 IRQs

Post by lidnariq » Mon Jan 07, 2019 2:23 pm

The only direct evidence we have so far is the picture Overload took of "The Flintstones: The Rescue of Dino & Hoppy"-
source: talk page for mapper 33
source: talk page for mapper 33
taito-tc0690fmi-mw22745.jpg (10.29 KiB) Viewed 13346 times
On this board ("J9100300A") there is also a 74LS157 wired up to serve as a transparent latch, where it holds copies of PPU A12 and PPU A13 ... I can't see all the signals but I think it's transparent while PPU/RD is high ... and these latched copies then go to the TC0690.

Given my understanding of how the PPU fetch cadence works, I don't see how that would change anything.

NewRisingSun
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Re: Taito TC0690 IRQs

Post by NewRisingSun » Mon Jan 07, 2019 5:54 pm

That reads like a circuit to prevent clocking the scanline counter when writing to $2006 mid-frame. Unfortunately, neither Flintstones not Jetsons do that (Flintstones at least not pre-IRQ), so it is unrelated.
Last edited by NewRisingSun on Mon Jan 07, 2019 6:01 pm, edited 1 time in total.

lidnariq
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Re: Taito TC0690 IRQs

Post by lidnariq » Mon Jan 07, 2019 6:00 pm

Shouldn't that be the other way? It only holds the value (and rejects new ones) when PPU/RD is low. (I mean, assuming I'm guessing connectivity correctly)

NewRisingSun
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Re: Taito TC0690 IRQs

Post by NewRisingSun » Mon Jan 07, 2019 6:05 pm

If the passed-on value is the latched one during one state of PPU /RD and transparent during the other, either A12/A13 changes are not passed on to the chip during reads or during writes. Certainly, it will not be that only write-cycle A12/A13 are fed to the scanline counter, because that would render it inoperational.

lidnariq
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Re: Taito TC0690 IRQs

Post by lidnariq » Mon Jan 07, 2019 7:56 pm

Right, but I interpreted what you were saying to mean that it was there to keep raster effects (mid-render writes to $2006) from incorrectly clocking the counter...

If my assumption about the connectivity is correct, namely it only passes through values when it's not fetching from the PPU's bus, then any random $2006 writes would pass through and clock the counter unhelpfully.

If I'm misreading it, and it's only transparent during PPU reads, then yes that would keep writes to $2006 during blanking from incorrectly clocking the counter...

Great Hierophant
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Re: Taito TC0690 IRQs

Post by Great Hierophant » Tue Jan 08, 2019 11:23 pm

A source whom I have no reason to doubt indicates that Famicom Jetsons does not show glitches on the title screen : https://www.famicomworld.com/forum/inde ... #msg183044 So I guess that it's behavior is a variant compared to Flintstones.

NewRisingSun
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Re: Taito TC0690 IRQs

Post by NewRisingSun » Wed Jan 09, 2019 1:34 pm

lidnariq wrote:If my assumption about the connectivity is correct, namely it only passes through values when it's not fetching from the PPU's bus
I am unsuccessfully trying to wrap my head around what exactly it means when you are only passing through values when the PPU is NOT reading, and what the purpose of such a thing would be. Unless the game is writing, won't the address that is then passed on just be what the PPU was reading from earlier? So is it basically just a delay?

lidnariq
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Re: Taito TC0690 IRQs

Post by lidnariq » Wed Jan 09, 2019 2:01 pm

NewRisingSun wrote:and what the purpose of such a thing would be.
That is exactly where I'm getting stuck also.
Unless the game is writing,
Writing vs not isn't relevant here... PPU /WR definitely does not proceed from the card edge.
So is it basically just a delay?
I'm not even convinced it's a delay? Beyond the standard 74LS TTL propagation delay, anyway. Which may have been accidentally enough for whatever they needed.

The only signals in the area at all are PPU/RD, CIRAM A10, and CHR banking outputs A12, A15, A16.

krzysiobal
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Re: Taito TC0690 IRQs

Post by krzysiobal » Thu Aug 01, 2019 4:09 pm

I bought original Flintstones to test the TC0690 chip.

On real hardware (NTSC console) Flintstones run fine. I swapped the EPROMs for the ones with pre-programmed Jetsons ROMs and there is the scanline artifact (see attached videos).
Flintstones: https://youtu.be/fdR8Reo8xFU
Jetsons: https://youtu.be/eQ64sxrECQI

Image Image Image Image Image

---

The TC0690 pinout on this particular cartridge is following.

Code: Select all

 
                              _____ 
                      n/c -- /01 64\ -- n/c
                     n/c -- /02   63\ -- n/c
                CHR A15 <- /03 (o) 62\ -> CHR A16
               PPU /RD <- /04       61\ -> CHR A11 
              CHR A18 <- /05         60\ -- n/c
             CHR A10 <- /06           59\ -- GND
         PPU A12MUX -> /07             58\ <- CPU D3
           PPU A11 -> /08               57\ -- VCC
              VCC -- /09                 56\ <- CPU D2
         PPU A10 -> /10                   55\ <- CPU D4
            GND -- /11                     54\ <- CPU D1
       CHR A13 -> /12                       53\ <- CPU D5
   PPU A13MUX -> /13    TAITO TC0690FMI      52\ -- n/c
     CHR A14 <- /14                          51/ -- n/c 
    CHR A12 <- /15                          50/ -- n/c
 CIRAM A10 <- /16                          49/ -- n/c
  CHR A17 <- /17                          48/ <- CPU D0 
     n/c -- /18                          47/ <- CPU A1
    n/c -- /19                          46/ <- CPU D6
    n/c -- \20                         45/ <- CPU A0 
    /IRQ <- \21                       44/ <- CPU D7
  /ROMSEL -> \22                     43/ -- GND
   PRG /CE <- \23                   42/ -> CHR /CE
    CPU R/W -> \24                 41/ -- VCC
         VCC -- \25               40/ <- M2
      PRG A15 <- \26             39/ -- n/c
           GND -- \27           38/ -> PRG A17
        PRG A13 <- \28         37/ <- CPU A13
         CPU A14 -> \29       36/ -> PRG A18
          PRG A16 <- \30     35/ -> PRG A14
               n/c -- \31   34/ -- n/c
                n/c -- \32 33/ -- n/c
                        \   / 
                         \ / 
I was particulary curious about the huge amount of unconnected pins, so:
* 1, 2, 18, 19, 20, 31, 32, 33, 34, 39, 49, 50, 51, 52, 60, 63, 64 - no signs of any internal connection (multimeter diode test to GND/VCC)
* 5 - CHR A18 (because TC0690 does not ignore D0 unlike MMC3 when setting 2k CHR banks, it is possible to access 512kB CHR memory but only using 2k banks)
* 36 - PRG A18

--

IRQ seems to behave differently that in the MMC3:

Code: Select all

   048  -  MMC3
 ---------------
  $C000   $C000 irq latch 
  $C001   $C001 irq reload
  $C002   $E001 irq en
  $C003   $E000 irq dis
* Mechanism of IRQS:

Code: Select all

  if falling_edge(PPU_/RD)
    if PPU_A13 = 0 AND LAST_PPU_A12 = 1 AND PPU_A12 = 0
      if (IRQ_counter = 255)
        IRQ_pending <= 1;
      end if;
      IRQ_counter++;
    end if;
    LAST_PPU_A12 <= PPU_A12
  end if

* IRQ is asserted immediatelly if IRQ_pending flag is set AND IRQs_are_enabled
* It is impossible to tell if the IRQ_counter is reloaded instantly when writing to C001 or when falling edge of PPU /RD (but that does not matter)
* Only writing to C001 clears the IRQ_pending flag (dislabling IRQs doesn't)
* IRQ counter reacts only when there is a PPU A12 transition at $0000-$1fff and only during PPU reads (because the external 74157 mux prevents chip from seeing actual PPU A12/A13 values during PPU write cycles)
* IRQ counter does not checks for M2 when determining if two A12 transitions are too close to each other

Image

NewRisingSun
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Re: Taito TC0690 IRQs

Post by NewRisingSun » Thu Aug 01, 2019 4:41 pm

Thank-you. This means that the Japanese Jetsons cartridge will either just display the glitchy scanline, or if it does not, then the IC on the Jetsons cartridge must implement the IRQ differently. If the latter turns out to be the case, then a submapper would need to be assigned.

Edit: The blurry togemet screenshot Great Hierophant linked to that purports to show that the scanline is not glitched on real hardware when using the real Jetsons cartridge no longer seems to be online.

lidnariq
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Re: Taito TC0690 IRQs

Post by lidnariq » Thu Aug 01, 2019 5:27 pm

krzysiobal wrote:* 5 - CHR A18 (because TC0690 does not ignore D0 unlike MMC3 when setting 2k CHR banks, it is possible to access 512kB CHR memory but only using 2k banks)
Interesting that they retained that functionality from the TC0190. Too bad there's no obvious way to change CHR A18 for the 1KB banks.
* IRQ counter reacts only when there is a PPU A12 transition at $0000-$1fff and only during PPU reads (because the external 74157 mux prevents chip from seeing actual PPU A12/A13 values during PPU write cycles)
Am I still misreading the PCB? While /PPURD is high, doesn't PPU A12 go through continuously? The value is only in the feedback path while /PPURD is low, right?
* Only writing to C001 clears the IRQ_pending flag (dislabling IRQs doesn't)
This is also weird, because in the above-linked thread, Sour said that
Sour wrote:that one time I spent hours on that Flintstones game. FYI, the game also requires that writing to $C000 acknowledges the IRQ, otherwise one specific portion of a later stage in the game is bugged

Great Hierophant
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Re: Taito TC0690 IRQs

Post by Great Hierophant » Sat May 02, 2020 5:43 pm

I was having a hard time finding copies of The Jetsons on eBay, then two popped up for sale. At first, I thought the cartridge shell was suspicious because it used a unique rounded-top cartridge I had never seen before with a Taito NES game. However, Bubble Bobble 2 and Captain Saver also use this cartridge style and apparently are the only Taito games that do.

Using a certain person's highly accurate emulator which supports IRQ timing switching between "Flintstones Correct" and "Jetsons Friendly", I found that neither Captain Saver nor Bubble Bobble 2 show different behavior when the timing is switched. So if all three games are using a unique shell, is it beyond the realm of possibility that they are using a new board with possibly different hardware on it? Of course, all three games are very expensive like Flintstones. Flintstones, Don Doko Don 2 or Bakushou!! Jinsei Gekijou 3 all share the same cartridge style with the bottom right corner cut from the label, which other Taito games use as well. I suppose no one has ever seen the picture of the insides of Bubble Bobble 2 or Captain Saver?

Great Hierophant
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Re: Taito TC0690 IRQs

Post by Great Hierophant » Fri May 22, 2020 9:53 am

After reviewing all the evidence, I am firmly convinced that the behavior in The Jetsons (Japan) as is currently produced by almost every emulator, is incorrect.

Everyone agrees that the MMC3 and the Taito TC0690's IRQ counters operate very similarly. The chief differences between them is that the latch reload values are opposite to each other and the timing is different by 4-6 cycles. In Flintstones, simulating the MMC3 timing will cause the first line of the status bar to scroll. We have opened a Flintstones cartridge and confirmed the correct behavior on original hardware. In Jetsons, simulating the TC0690's IRQ timing causes junk pixels underneath the title on the title screen and the split in the entering level screen to be partway across the screen.

Consider the release dates of Mapper 48 games :

The Flintstones Japan - 08/07/1991
The Flintstones USA - 12/1991
Bakushou!! Jinsei Gekijou 3 - 12/10/1991
Don Doko Don 2 - 01/31/1992
Captain Saver - 09/29/1992
Power Blade II - 10/1992
The Jetsons USA - 12/1992
Bubble Bobble 2 Japan - 03/05/1993
The Jetsons Japan - 04/23/1993
Bubble Bobble Part 2 USA - 08/1993

Flintstones, Bakushou!! Jinsei Gekijou 3 and Don Doko Don 2 all were released well before Taito updated their cartridge shell design for Captain Saver. In those months, Taito could have revised their TC0690 mask to adjust the timing. The programmers may have complained that the timing differences between MMC3 and the Taito chip were a nuisance and they were developing at least one game, Jetsons, primarily for U.S. audiences and had to use the MMC3 chip for that game's USA release.

I decided to try to see if it would be possible to get Jetsons (Japan) to display like Jetsons (USA) on the TC0690 using the standard TC0690 timing. After much education and blundering I succeeded.

Jetson's scanline IRQ handler appears to be called in three separate locations in the code. The first handles the scanline IRQ on the title screen, the second handles the scanline IRQ on the entering level screen and the third handles the scanline IRQ on the main gameplay screen. With a tweak of the IRQ reload counter values by one or two the junk on the title screen was gone and the split on the entering level screen occurred in the sample place as it does on Jetsons (USA). Here are the changes :

056F6 - D2 to D1
1C48D - C3 to BF
1C8F6 - AA to A8

So with three bytes, you can see Jetsons (Japan) as I believe it was intended to look on a Famicom and my Famicom World source indicated it did look on his Famicom (his post and picture are now deleted). Incidentally, if you XOR the latch value with FF to get the MMC3 equivalent value for the untouched Jetsons (Japan), those values match the values that Jetsons (USA) used in the same places. Given the relative simplicity of this adjustment, I doubt the programmers would have permitted such sloppiness to have made its way out the door and there is no visual evidence that they did. Nor has anyone pointed to unusual behavior in Jetsons which might select slightly different timing in the TC0690 for this game.

No one has ever opened a Jetsons, Captain Saver or Bubble Bobble 2 cartridge because they are quite expensive, going for $250-400 on eBay. Even without this I believe that the reasoning I have outlined above makes a compelling case that at least Jetsons needs a submapper 48.1 designating "TC0690 with MMC3 IRQ Counter timing."

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