pc9801.cpp: Eliminate bogus XTALs (nw)

src/devices/bus/cbus/pc9801_26.cpp

@@ -18,8 +18,6 @@
 #include "speaker.h"
 
 
-#define MAIN_CLOCK_X1 XTAL(1'996'800)
-
 //**************************************************************************
 //  GLOBAL VARIABLES
 //**************************************************************************
@@ -40,7 +38,7 @@ WRITE_LINE_MEMBER(pc9801_26_device::sound_irq)
 
 MACHINE_CONFIG_START(pc9801_26_device::device_add_mconfig)
 	SPEAKER(config, "mono").front_center();
-	MCFG_DEVICE_ADD("opn", YM2203, MAIN_CLOCK_X1*2) // unknown clock / divider
+	MCFG_DEVICE_ADD("opn", YM2203, 15.9744_MHz_XTAL / 4) // divider not verified
 	MCFG_YM2203_IRQ_HANDLER(WRITELINE(*this, pc9801_26_device, sound_irq))
 	MCFG_AY8910_PORT_A_READ_CB(READ8(*this, pc9801_26_device, opn_porta_r))
 	//MCFG_AY8910_PORT_B_READ_CB(READ8(*this, pc9801_state, opn_portb_r))

src/devices/bus/cbus/pc9801_amd98.cpp

@@ -32,8 +32,6 @@
 #include "speaker.h"
 
 
-#define MAIN_CLOCK_X1 XTAL(1'996'800)
-
 //**************************************************************************
 //  GLOBAL VARIABLES
 //**************************************************************************
@@ -48,17 +46,17 @@ DEFINE_DEVICE_TYPE(PC9801_AMD98, pc9801_amd98_device, "pc9801_amd98", "pc9801_am
 MACHINE_CONFIG_START(pc9801_amd98_device::device_add_mconfig)
 	SPEAKER(config, "lspeaker").front_left();
 	SPEAKER(config, "rspeaker").front_right();
-	MCFG_DEVICE_ADD("ay1", AY8910, MAIN_CLOCK_X1*2)
+	MCFG_DEVICE_ADD("ay1", AY8910, 1'996'800)
 	MCFG_AY8910_PORT_A_READ_CB(IOPORT("OPN_PA1"))
 	MCFG_AY8910_PORT_B_WRITE_CB(WRITE8(*this, pc9801_amd98_device,ay3_address_w))
 	MCFG_SOUND_ROUTE(ALL_OUTPUTS, "lspeaker", 0.50)
 
-	MCFG_DEVICE_ADD("ay2", AY8910, MAIN_CLOCK_X1*2)
+	MCFG_DEVICE_ADD("ay2", AY8910, 1'996'800)
 	MCFG_AY8910_PORT_A_READ_CB(IOPORT("OPN_PA2"))
 	MCFG_AY8910_PORT_B_WRITE_CB(WRITE8(*this, pc9801_amd98_device,ay3_data_latch_w))
 	MCFG_SOUND_ROUTE(ALL_OUTPUTS, "rspeaker", 0.50)
 
-	MCFG_DEVICE_ADD("ay3", AY8910, MAIN_CLOCK_X1*2)
+	MCFG_DEVICE_ADD("ay3", AY8910, 1'996'800)
 	MCFG_SOUND_ROUTE(ALL_OUTPUTS, "lspeaker", 0.25)
 	MCFG_SOUND_ROUTE(ALL_OUTPUTS, "rspeaker", 0.25)
 MACHINE_CONFIG_END

src/emu/xtal.cpp

@@ -75,11 +75,10 @@ const double XTAL::known_xtals[] = {
 	  1'750'000, /* 1.75_MHz_XTAL          RCA CDP1861 */
 	  1'797'100, /* 1.7971_MHz_XTAL        SWTPC 6800 (with MIKBUG) */
 	  1'843'200, /* 1.8432_MHz_XTAL        Bondwell 12/14 */
-	  1'996'800, /* 1.9968_MHz_XTAL        NEC PC-98xx */
 	  2'000'000, /* 2_MHz_XTAL             - */
 	  2'012'160, /* 2.01216_MHz_XTAL       Cidelsa Draco sound board */
 	  2'097'152, /* 2.097152_MHz_XTAL      Icatel 1995 - Brazilian public payphone */
-	  2'457'600, /* 2.4576_MHz_XTAL        Atari ST MFP, NEC PC-98xx */
+	  2'457'600, /* 2.4576_MHz_XTAL        Atari ST MFP */
 	  2'500'000, /* 2.5_MHz_XTAL           Janken Man units */
 	  2'950'000, /* 2.95_MHz_XTAL          Playmatic MPU-C, MPU-III & Sound-3 */
 	  3'000'000, /* 3_MHz_XTAL             Probably only used to drive 68705 or similar MCUs on 80's Taito PCBs */

src/mame/drivers/pc9801.cpp

@@ -1798,13 +1798,14 @@ READ8_MEMBER(pc9801_state::get_slave_ack)
 *
 ****************************************/
 
-/* basically, PC-98xx series has two xtals.
+/* These rates do NOT appear to represent actual XTALs. They are likely obtained in
-   My guess is that both are on the PCB, and they clocks the various system components.
+   different ways on different PC-98 models as divisions of extant XTAL frequencies
+   such as 14.7456 MHz, 15.9744 MHz, 19.6608 MHz and 23.9616 MHz.
    PC-9801RS needs X1 for the pit, otherwise Uchiyama Aki no Chou Bangai has sound pitch bugs
    PC-9821 definitely needs X2, otherwise there's a timer error at POST. Unless it needs a different clock anyway ...
    */
-#define MAIN_CLOCK_X1 XTAL(1'996'800)
+#define MAIN_CLOCK_X1 1'996'800
-#define MAIN_CLOCK_X2 XTAL(2'457'600)
+#define MAIN_CLOCK_X2 2'457'600
 
 /****************************************
 *