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◆ main openmsx / src / video / v9990 / V9990DisplayTiming.hh
3.0 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#ifndef V9990DISPLAYTIMING_HH
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#define V9990DISPLAYTIMING_HH
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namespace openmsx {
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/** A period, either horizontal or vertical, starts with a synchronisation
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  * pulse followed by a blank period. Then border, display and border are
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  * output follow. The final blank between the last border period and the
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  * following sync signal is not included -- we don't need it.
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  */
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struct V9990DisplayPeriod
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{
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	int cycle;
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	int blank;
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	int border1;
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	int display;
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	int border2;
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};
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class V9990DisplayTiming
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{
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public:
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	/** The V9990 has an internal clock (MCLK @ 14MHz) and a terminal
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	  * for an external clock (XTAL1), which can be connected to a 21
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	  * or 25 MHz crystal. The Gfx9000 provides an 21 MHz crystal.
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	  *
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	  * The emulation combines these two clocks into one unified
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	  * clock (UC) running at 42MHz - the smallest common multiple
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	  * of 14 and 21 MHz.
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	  */
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	static constexpr int UC_TICKS_PER_SECOND = 3579545 * 12; // 42.9MHz
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	/** The number of clock ticks per line is independent of the crystal
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	  * used or the display mode (NTSC/PAL)
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	  */
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	static constexpr int UC_TICKS_PER_LINE = 2736;
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	/** Horizontal (line) timing when using MCLK:
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	  * 'Normal' display modes. Timing is in UC ticks.
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	  */
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	static constexpr auto lineMCLK = V9990DisplayPeriod{
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		.cycle = V9990DisplayTiming::UC_TICKS_PER_LINE, .blank = 400, .border1 = 112, .display = 2048, .border2 = 112};
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	/** Horizontal (line) timing when using XTAL:
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	  *'Overscan' modes without border. Timing is in UC ticks.
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	  */
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	static constexpr auto lineXTAL = V9990DisplayPeriod{
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		.cycle = V9990DisplayTiming::UC_TICKS_PER_LINE, .blank = 372, .border1 = 0, .display = 2304, .border2 = 0};
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	/** NTSC display timing, when using MCLK:
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	  * Normal display mode with borders. Timing is in display lines.
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	  */
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	static constexpr auto displayNTSC_MCLK = V9990DisplayPeriod{
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		.cycle = 262, .blank = 15, .border1 = 14, .display = 212, .border2 = 14};
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	/** NTSC display timing, when using XTAL:
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	  * Overscan mode without borders. Timing is in display lines.
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	  */
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	static constexpr auto displayNTSC_XTAL = V9990DisplayPeriod{
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		.cycle = 262, .blank = 15, .border1 = 0, .display = 240, .border2 = 0};
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	/** PAL display timing, when using MCLK:
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	  * Normal display mode with borders. Timing is in display lines.
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	  */
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	static constexpr auto displayPAL_MCLK = V9990DisplayPeriod{
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		.cycle = 313, .blank = 15, .border1 = 41, .display = 212, .border2 = 37};
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	/** PAL display timing, when using XTAL:
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	  * Overscan mode without borders. Timing is in display lines.
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	  */
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	static constexpr auto displayPAL_XTAL = V9990DisplayPeriod{
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		.cycle = 313, .blank = 15, .border1 = 0, .display = 290, .border2 = 0};
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	/** Get the number of UC ticks in 1 frame.
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	  * @param  palTiming  Use PAL timing? (False = NTSC timing)
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	  * @return            The number of UC ticks in a frame
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	  */
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	[[nodiscard]] static constexpr int getUCTicksPerFrame(bool palTiming) {
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		return palTiming ? (displayPAL_MCLK.cycle  * UC_TICKS_PER_LINE)
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		                 : (displayNTSC_MCLK.cycle * UC_TICKS_PER_LINE);
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	}
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};
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} // openmsx
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#endif