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(MESS) maria.c: improved DMA accuracy. [Mike Saarna, Robert Tuccitto]

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- Last Line DMA value corrected to 6. GCC and Atari docs both show a 
    difference between Other Line and Last Line as +6 at the lowest part 
    of the range.
  - Blank scanlines are drawn when DMA is off, like real hardware.
  - If MARIA hits the DMA limit, the CPU doesn't run until the next 
    scanline.
This commit is contained in:
Fabio Priuli 2014-10-10 05:03:12 +00:00
parent 0ed3636613
commit 9f7b18a05c
1 changed files with 104 additions and 83 deletions
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35
src/mess/video/maria.c
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@ -4,7 +4,16 @@
- some history:
2014-10-03 Mike Saarna, Robert Tuccitto reorganized DMA penalties to
2014-10-05 Mike Saarna, Robert Tuccitto Last Line DMA value corrected
to 6. GCC and Atari docs both show a difference between
Other Line and Last Line as +6 at the lowest part of the
range.
Blank scanlines are drawn when DMA is off, like real
hardware.
If MARIA hits the DMA limit, the CPU doesn't run until
the next scanline.
2014-09-03 Mike Saarna, Robert Tuccitto reorganized DMA penalties to
support new rendering timeout code.
2014-08-29 Mike Saarna Timeout rendering added.
@ -165,18 +174,22 @@ void atari_maria_device::draw_scanline()
int d, c, pixel_cell, cells;
int maria_cycles;
cells = 0;
if(m_dmaon)
{
// All lines in a zone have the same initial DMA startup time. We'll adjust
// cycles for the special last zone line later, as those penalties happen after
// MARIA is done rendering, or after its hit the maximum rendering time.
maria_cycles = 16;
cells = 0;
/* Process this DLL entry */
dl = m_dl;
/* DMA */
/* Step through DL's while we're within maximum rendering time. max render time = ( scanline length - DMA start ) */
/* Step through DL's while we're within maximum rendering time. */
/* max render time = ( scanline length - DMA start ) */
/* 426 = ( 454 - 28 ) */
while (((READ_MEM(dl + 1) & 0x5f) != 0) && (maria_cycles<426))
@ -251,9 +264,16 @@ void atari_maria_device::draw_scanline()
// Last Line post-render DMA cycle penalties...
if (m_offset == 0)
{
maria_cycles += 3; // extra shutdown time
maria_cycles += 6; // extra shutdown time
if (READ_MEM(m_dll + 3) & 0x80)
maria_cycles += 21; // interrupt overhead
maria_cycles += 17; // interrupt overhead
}
// If MARIA used up all of the DMA time then the CPU can't run until next line...
if (maria_cycles>=426)
{
m_cpu->spin_until_trigger(TRIGGER_HSYNC);
m_wsync = 1;
}
// Spin the CPU for Maria DMA, if it's not already spinning for WSYNC.
@ -262,6 +282,7 @@ void atari_maria_device::draw_scanline()
// To spin until an even divisor, we just round-up any would-be truncations by adding 3.
if (!m_wsync)
m_cpu->spin_until_time(m_cpu->cycles_to_attotime((maria_cycles+3)/4));
}
// draw line buffer to screen
m_active_buffer = !m_active_buffer; // switch buffers
@ -335,13 +356,13 @@ void atari_maria_device::startdma(int lines)
m_holey = (READ_MEM(m_dll) & 0x60) >> 5;
m_nmi = READ_MEM(m_dll) & 0x80;
/* logerror("DLL=%x\n",m_dll); */
draw_scanline();
}
if ((frame_scanline > 15) && (frame_scanline < (lines - 5)))
draw_scanline();
if ((frame_scanline > 16) && (frame_scanline < (lines - 5)) && m_dmaon)
{
draw_scanline();
if (m_offset == 0)
{
m_dll += 3;