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[Core/VDP] improved FIFO emulation accuracy

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EkeEke 2017-06-05 23:52:03 +02:00
parent ee0fd881f6
commit 38ffc317cb
5 changed files with 16 additions and 11 deletions
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25
core/vdp_ctrl.c
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@ -5,7 +5,7 @@
* Support for SG-1000 (TMS99xx & 315-5066), Master System (315-5124 & 315-5246), Game Gear & Mega Drive VDP
*
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2016 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2007-2017 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met:
@ -2039,7 +2039,7 @@ static void vdp_reg_w(unsigned int r, unsigned int d, unsigned int cycles)
static void vdp_fifo_update(unsigned int cycles)
{
int slots, count = 0;
int num, slots, count = 0;
const int *fifo_timing;
@ -2075,13 +2075,13 @@ static void vdp_fifo_update(unsigned int cycles)
count++;
}
/* number of processed FIFO entries since last access */
slots = (slots + count - fifo_slots) >> fifo_byte_access;
/* number of processed FIFO entries since last access (byte access needs two slots to process one FIFO word) */
num = (slots + count - fifo_slots) >> fifo_byte_access;
if (slots > 0)
if (num > 0)
{
/* process FIFO entries */
fifo_write_cnt -= slots;
fifo_write_cnt -= num;
/* Clear FIFO full flag */
status &= 0xFEFF;
@ -2093,14 +2093,19 @@ static void vdp_fifo_update(unsigned int cycles)
/* Set FIFO empty flag */
status |= 0x200;
}
/* Update FIFO access slot counter */
fifo_slots += (slots << fifo_byte_access);
/* Reinitialize FIFO access slot counter */
fifo_slots = slots + count;
}
else
{
/* Update FIFO access slot counter */
fifo_slots += (num << fifo_byte_access);
}
}
/* next FIFO update cycle */
fifo_cycles = mcycles_vdp + fifo_timing[count | fifo_byte_access];
fifo_cycles = mcycles_vdp + fifo_timing[fifo_slots - slots + fifo_byte_access];
}

2
core/vdp_ctrl.h
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@ -5,7 +5,7 @@
* Support for SG-1000 (TMS99xx & 315-5066), Master System (315-5124 & 315-5246), Game Gear & Mega Drive VDP
*
* Copyright (C) 1998-2003 Charles Mac Donald (original code)
* Copyright (C) 2007-2016 Eke-Eke (Genesis Plus GX)
* Copyright (C) 2007-2017 Eke-Eke (Genesis Plus GX)
*
* Redistribution and use of this code or any derivative works are permitted
* provided that the following conditions are met: