Warlords fix for XRGB-mini

Entry posted by SpiceWare · August 22, 2015

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In this topic about the exciting new RGB mod for the 2600, collinp reported that the XRGB-mini had problems syncing with Warlords.

I took a quick look and noticed that VSYNC was set before the WSYNC, instead of after, which resulted in the sync signal starting late in the scanline.

I did a quick hack via Stella to swap the order. The hack resulted in the kings getting shifted to the right, but was enough for collinp to confirm that moving the VSYNC after the WSYNC did indeed fix the problem.

Today I fixed the sync and king positions by modifying the source I documented back in 2006. The source can be used to compile the original ROM or an XRGB-mini compatible build by use of the constant XRGBMINI:

; set to 1 for VSYNC fix for XRGBMINI, set to 0 for original
XRGBMINI    = 1

...

StartOfFrame: 
       LDA    #$82        ; P-----V- P-paddles are dumped to ground, V-vertical Blank is started
       
   if XRGBMINI = 1
       ldx #$50           ; move left 5
       STA    VBLANK  
       STA    WSYNC       ; Wait until end of 1st V-Sync scan Line
       STA    VSYNC       ; Start Vertical Sync
       STX    HMM0
       STX    HMM1
   else
       STA    VBLANK  
       STA    VSYNC       ; Start Vertical Sync
       STA    WSYNC       ; Wait until end of 1st V-Sync scan Line
       LDA    #$20        ; Move Left 2
       STA    HMM0        ; 3 5
       STA    HMM1        ; 3 8
   endif

ROM

warlords_xrgbmini.bin

Source

warlords.asm

Defender

defender_vsync.bin

defender_vblank.bin

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