video/upd7220.cpp: implement experimental partition fetch fn

nec/pc9821.cpp: add 31 kHz monitor setting

src/devices/video/upd7220.cpp

@@ -392,6 +392,11 @@ inline void upd7220_device::update_blank_timer(int state)
 //  recompute_parameters -
 //-------------------------------------------------
 
+void upd7220_device::device_clock_changed()
+{
+	recompute_parameters();
+}
+
 inline void upd7220_device::recompute_parameters()
 {
 	// microbx2 wants horizontal multiplier of x16
@@ -613,6 +618,19 @@ inline void upd7220_device::get_graphics_partition(int index, uint32_t *sad, uin
 	*wd = BIT(m_ra[(index * 4) + 3], 7);
 }
 
+/*
+ * experimental, for non-canonical stuff such as PC9821 PEGC
+ */
+std::tuple<u32, u16, u8> upd7220_device::get_area_partition_props(int line)
+{
+	uint32_t sad;
+	uint16_t len;
+	int im, wd;
+	// TODO: multiareas (pc9821:skinpan title)
+	get_graphics_partition(0, &sad, &len, &im, &wd);
+
+	return std::make_tuple(sad, m_pitch, im);
+}
 
 
 //**************************************************************************
@@ -1838,12 +1856,12 @@ void upd7220_device::update_graphics(bitmap_rgb32 &bitmap, const rectangle &clip
 		{
 			// according to documentation only areas 0-1-2 can be drawn in bitmap mode
 			// - pc98:quarth definitely needs area 2 for player section.
-            // - pc98:steamhea wants area 3 for scrolling and dialogue screens to work together,
-            //   contradicting the doc. Fixed in 7220A or applies just for mixed mode?
+			// - pc98:steamhea wants area 3 for scrolling and dialogue screens to work together,
+			//   contradicting the doc. Fixed in 7220A or applies just for mixed mode?
 			// TODO: what happens if combined area size is smaller than display height?
 			// documentation suggests that it should repeat from area 0, needs real HW verification (no known SW do it).
 			if (area >= 3 && !force_bitmap)
-                break;
+				break;
 
 			// pc98:madoum1-3 sets up ALL areas to a length of 0 after initial intro screen.
 			// madoum1: area 0 sad==0 on gameplay (PC=0x955e7), sad==0xaa0 on second intro screen (tower) then intentionally scrolls up and back to initial position.

src/devices/video/upd7220.h

@@ -87,6 +87,8 @@ public:
 	void ext_sync_w(int state);
 	void lpen_w(int state);
 
+	std::tuple<u32, u16, u8> get_area_partition_props(int line);
+
 	uint32_t screen_update(screen_device &screen, bitmap_rgb32 &bitmap, const rectangle &cliprect);
 
 protected:
@@ -100,6 +102,7 @@ protected:
 	virtual space_config_vector memory_space_config() const override;
 
 	virtual int translate_command(uint8_t data);
+	virtual void device_clock_changed() override;
 
 	TIMER_CALLBACK_MEMBER(hsync_update);
 	TIMER_CALLBACK_MEMBER(vsync_update);

src/mame/nec/pc9821.cpp

@@ -51,32 +51,35 @@ uint32_t pc9821_state::screen_update(screen_device &screen, bitmap_rgb32 &bitmap
 
 	if(m_video_ff[DISPLAY_REG] != 0)
 	{
-		// TODO: following is wrong: definitely requires GDC latches
-		// flashb (pitch=512) and skinpan (two areas on title screen)
-		// aitd sets pitch=40, which means something else inside 7220 should do the bump.
-
-		// PEGC 256 mode is linear VRAM picked from a specific VRAM buffer.
-		// It doesn't latch values from GDC, it runs on its own renderer instead.
-		// Is the DAC really merging two pixels not unlike VGA correlated Mode 13h?
-		// https://github.com/joncampbell123/dosbox-x/issues/1289#issuecomment-543025016
-		// TODO: getter cliprect from bitmap GDC
 		if (m_ex_video_ff[ANALOG_256_MODE])
 		{
 			rgb_t const *const palette = m_palette->palette()->entry_list_raw();
 			u8 *ext_gvram = (u8 *)m_ext_gvram.target();
 			int base_y = cliprect.min_y;
+			u32 base_address;
+			u16 pitch;
+			u8 im;
 
 			for (int y = cliprect.min_y; y <= cliprect.max_y; y++)
 			{
+				const int rel_y = y - base_y;
+
+				std::tie(base_address, pitch, im) = m_hgdc[1]->get_area_partition_props(rel_y);
+				// aitd sets PITCH=40 (320), guess: assume im == 0 doing the trick
+				const u8 pitch_shift = im ^ 1;
+
 				for (int x = cliprect.min_x; x <= cliprect.max_x; x += 8)
 				{
-					u32 address = (y - base_y) * (640 / 8) + (x >> 3);
+					// Mask is confirmed by flashb:
+					// does double buffering at SAD $38fc and $fffc, except when
+					// it goes single on title, drawing on current bank displayed.
+					u32 address = (((base_address << 1) + (rel_y) * (pitch << pitch_shift) + (x >> 3)) & 0xffff) << 3;
 					for(int xi = 0; xi < 8; xi ++)
 					{
 						int res_x = x + xi;
 						int res_y = y;
 
-						u16 pen = ext_gvram[(address << 3) + xi + (m_vram_disp * 0x40000)];
+						u16 pen = ext_gvram[(address + xi) + (m_vram_disp * 0x40000)];
 
 						bitmap.pix(res_y, res_x) = palette[(pen & 0xff) + 0x20];
 					}
@@ -307,20 +310,17 @@ void pc9821_state::pc9821_mode_ff_w(u8 data)
 {
 	const u8 mode_ff = data & 0xfe;
 	const u8 setting = BIT(data, 0);
-	// Monitor setting
+	// 24/31 kHz Monitor setting
 	// BA / BX / PC-H98 / PC-9821 / 98NOTE uses this f/f in place of 15/24 kHz switch
 	// TODO: better compose
+	// TODO: both frequencies needs to be verified
+	// 31 kHz from standard VGA clock (flashb)
 	if (mode_ff == 0x20)
 	{
-		if (!setting)
-		{
-			const XTAL screen_clock = XTAL(21'052'600) / 8;
+		const XTAL screen_clock = (setting ? XTAL(25'175'000) : XTAL(21'052'600)) / 8;
 
-			m_hgdc[0]->set_unscaled_clock(screen_clock);
-			m_hgdc[1]->set_unscaled_clock(screen_clock);
-		}
-		else
-			popmessage("pc9821_mode_ff_w: 31 kHz mode selected");
+		m_hgdc[0]->set_unscaled_clock(screen_clock);
+		m_hgdc[1]->set_unscaled_clock(screen_clock);
 	}
 }
 
@@ -338,7 +338,7 @@ void pc9821_state::pegc_mmio_map(address_map &map)
 	map(0x100, 0x100).lw8(
 		NAME([this] (u8 data) {
 			m_pegc.packed_mode = bool(BIT(data, 0));
-            logerror("$e0100 packed mode %02x\n", data);
+			logerror("$e0100 packed mode %02x\n", data);
 		})
 	);
 //  map(0x102, 0x102) enable pegc linear VRAM at upper addresses