ATARI 8 bit emulator

Posted Wed Jan 16, 2013 9:50 AM

Hi folks,

a new release of Atari++, the portable atari emulator for Linux and windows has been released here in the download section - as usual, you find there the Linux sources and a compiled version for 32-bit Windows. This release is how 1.70 should have been, but wasn't due to time constraints.

 Lots of fixes left over from 1.70 are now integrated, and regressions have been fixed:

  • The ANTIC logic to roll over an instruction to the next scan was partially  broken and also rolled a "Jump on Vertical Blank" over, breaking some games that played tricks with the DMA control register.
  • The new CPU logic to fetch the wrong interrupt vector (NMI instead of IRQ) was partially broken and forgot to fetch the right high-bit, potentially breaking code.
  • The 65C02 BRK instruction was emulated incorrectly. The NMOS version worked fine, and continues to work fine.
  • 1.70 had, as indicated, a regression for late writes on Antic CHARCTL that broke at least one game ("Summer Games"). The corresponding logic has been re-done in a much cleaner way and is now part of 1.71.
  • Pokey lo-byte timer registers in a 16-bit timer pair did not underrun to 255 correctly. In fact, the timer emulation was partially re-done and should now do correctly, including the relative offset of low and high-timer on a STIMER resynchronization.
  • GTIA priority logic for player 4 on top of playfield 0/1 was broken in one priority selection, which got fixed now.
  • Player/missile retriggering was partially incorrect. This has been fixed now.
  • Player/missile resizing was, as stated, experimental in 1.70 and is now implemented correctly.
  • On-line player/missile shape changes are now experimentally supported.
  • The ANTIC/CPU WSYNC logic was partially broken as it does not block writes, only reads - the mechanism is a different one. Note that this only holds for the NMOS version. The CMOS version works correctly. This is also emulated.
  • The NMI/IRQ reaction times were short by one cycle. They are now 7 cycles as indicated.
  • GTIA mode 80 on top of a low-res screen created a wrong color for the PF3:BK pixel combination. This got fixed.
  • GTIA VDelay support was partially broken. Actually, the P/M DMA engine was redesigned for this release and should now work correctly.
  • Alsa sound support was broken on some hardware. For some Alsa drivers, audio hardware reacts allergic when trying to fill more samples into the available buffer, stalling the main program. The updated Alsa sound support rounds the samples written to the Alsa buffer to entire fragment sizes avoiding this problem. The SDL or Oss/HQOss drivers were not affected, though in general Alsa is preferably.

Anti-News: (or, what does not yet work):
  • P/M shape changes are currently supported experimentally until I get hands on real hardware.
  • P/M shift-register disable tricks with PSIZE=2 are currently not supported.
  • Writes to GTIA color or priority registers are not delayed and happen immediately. The same goes to many other registers in Pokey, Antic and PIA.
  • Antic DMACtrl in-line adjustment tricks are not supported, neither any HScroll adjustments to disable the DMA-stop.
  • Bus noise picked up by GTIA if GRACTL is enabled but DMACTL is disabled is currently not emulated correctly.
  • Bus noise picked up by ANTIC on the right side of wide playfield screens is currently not emulated at all (and neither visible if it would).
  • The POKEY soft-reset cylce is currently not emulated completely.
  • Bit-banging serial output is currently not emulated at all.

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