diff options
Diffstat (limited to 'src/zx81.c')
| -rw-r--r-- | src/zx81.c | 27 |
1 files changed, 17 insertions, 10 deletions
@@ -78,6 +78,7 @@ static Z80Word RAMLEN=0; */ static int nmigen=FALSE; static int hsync=FALSE; +static int vsync=FALSE; /* The ULA */ @@ -390,9 +391,6 @@ static void ULA_Video_Shifter(Z80 *z80, Z80Byte val) } ULA.x=(ULA.x+1)&0x1f; - - if (ULA.x==0) - Z80Interrupt(z80,0xff); } @@ -410,6 +408,7 @@ static int CheckTimers(Z80 *z80, Z80Val val) else if (hsync) { Debug("HSYNC\n"); + Z80Interrupt(z80,0xff); if (ULA.release) { /* ULA.release=FALSE; */ @@ -608,13 +607,11 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port) break; } - /* Turn off HSYNC if NMI generator is OFF and redraw screen to - match output ULA has since sent out. + /* Turn on VSYNC if not on */ - if (!nmigen && hsync) + if (!vsync) { - Debug("HSYNC OFF\n"); - hsync=FALSE; + Debug("VSYNC\n"); GFXEndFrame(TRUE); GFXClear(white); @@ -625,6 +622,7 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port) ULA.release=FALSE; GFXStartFrame(); + vsync=TRUE; } else { @@ -633,6 +631,14 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port) ULA.c=0; ULA.release=FALSE; } + + /* If NMI on, turn off the HSYNC generator + */ + if (!nmigen) + { + Debug("HSYNC OFF\n"); + hsync=FALSE; + } break; default: @@ -645,7 +651,7 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port) void ZX81WritePort(Z80 *z80, Z80Word port, Z80Byte val) { - Debug("OUT %4.4x\n",port); + Debug("OUT %4.4x,%2.2X\n",port,val); /* Any port write releases the ULA line counter */ @@ -659,8 +665,9 @@ void ZX81WritePort(Z80 *z80, Z80Word port, Z80Byte val) break; case 0xfe: /* NMI generator ON */ - Debug("NMIGEN ON\n"); + Debug("NMIGEN ON/VSYNC OFF\n"); nmigen=TRUE; + vsync=FALSE; break; case 0xff: /* HSYNC generator ON */ |