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Add specific support for the fact that setting frequency to 0 does not behave as if frequency was set to 0x400 on the Sega-manufactured PSG clone chips, whereas it does on the original TI-made ones. Fixes Sega Master System 'Vigilante' music [Lord Nightmare, Enik]

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This commit is contained in:
Jonathan Gevaryahu 2011-02-24 04:53:09 +00:00
parent a123086b67
commit d14e3c7d09
1 changed files with 28 additions and 11 deletions
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39
src/emu/sound/sn76496.c
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@ -2,6 +2,7 @@
sn76496.c sn76496.c
by Nicola Salmoria by Nicola Salmoria
with contributions by others
Routines to emulate the: Routines to emulate the:
Texas Instruments SN76489, SN76489A, SN76494/SN76496 Texas Instruments SN76489, SN76489A, SN76494/SN76496
@ -25,9 +26,11 @@
** SN76494 is the same as SN76489A but lacks the /8 divider on its clock input. ** SN76494 is the same as SN76489A but lacks the /8 divider on its clock input.
** SN76496 is identical in operation to the SN76489A, but the audio input is ** SN76496 is identical in operation to the SN76489A, but the audio input is
documented. documented.
All the SN7xxxx chips have an audio input line which is mixed with the 4 channels All the TI-made PSG chips have an audio input line which is mixed with the 4 channels
of output. (It is undocumented and may not function properly on the sn76489, 76489a of output. (It is undocumented and may not function properly on the sn76489, 76489a
and 76494; the sn76489a input is mentioned in datasheets for the tms5200) and 76494; the sn76489a input is mentioned in datasheets for the tms5200)
All the TI-made PSG chips act as if the frequency was set to 0x400 if 0 is
written to the frequency register.
** Sega Master System III/MD/Genesis PSG uses a 16-bit shift register with taps ** Sega Master System III/MD/Genesis PSG uses a 16-bit shift register with taps
on bits C and F, output on F on bits C and F, output on F
It uses a 16-bit ring buffer for periodic noise/arbitrary duty cycle. It uses a 16-bit ring buffer for periodic noise/arbitrary duty cycle.
@ -39,6 +42,8 @@
for bits 7 6 5 4 3 2 1 0 for bits 7 6 5 4 3 2 1 0
L3 L2 L1 L0 R3 R2 R1 R0 L3 L2 L1 L0 R3 R2 R1 R0
Noise is an XOR function, and audio output is negated before being output. Noise is an XOR function, and audio output is negated before being output.
All the Sega-made PSG chips act as if the frequency was set to 0 if 0 is written
to the frequency register.
** NCR7496 (as used on the Tandy 1000) is similar to the SN76489 but with a ** NCR7496 (as used on the Tandy 1000) is similar to the SN76489 but with a
different noise LFSR patttern: taps on bits A and E, output on E different noise LFSR patttern: taps on bits A and E, output on E
It uses a 15-bit ring buffer for periodic noise/arbitrary duty cycle. It uses a 15-bit ring buffer for periodic noise/arbitrary duty cycle.
@ -94,12 +99,19 @@
Fix phase of noise on sn94624 and sn76489; all chips use a standard XOR, the only inversion is the output itself - LN, Plgdavid Fix phase of noise on sn94624 and sn76489; all chips use a standard XOR, the only inversion is the output itself - LN, Plgdavid
Thanks to PlgDavid and Michael Zapf for providing samples which helped immensely here. Thanks to PlgDavid and Michael Zapf for providing samples which helped immensely here.
23/02/2011: Lord Nightmare & Enik
Made it so the Sega PSG chips have a frequency of 0 if 0 is written to the
frequency register, while the others have 0x400 as before. Should fix a bug
or two on sega games, particularly Vigilante on Sega Master System. Verified
on SMS hardware.
TODO: * Implement the TMS9919 - any difference to sn94624? TODO: * Implement the TMS9919 - any difference to sn94624?
* Implement the T6W28; has registers in a weird order, needs writes * Implement the T6W28; has registers in a weird order, needs writes
to be 'sanitized' first. Also is stereo, similar to game gear. to be 'sanitized' first. Also is stereo, similar to game gear.
* Test the NCR7496; Smspower says the whitenoise taps are A and E, * Test the NCR7496; Smspower says the whitenoise taps are A and E,
but this needs verification on real hardware. but this needs verification on real hardware.
* Factor out common code so that the SAA1099 can share some code. * Factor out common code so that the SAA1099 can share some code.
* Convert to modern device
***************************************************************************/ ***************************************************************************/
#include "emu.h" #include "emu.h"
@ -131,6 +143,7 @@ struct _sn76496_state
INT32 Count[4]; /* Position within the waveform */ INT32 Count[4]; /* Position within the waveform */
INT32 Output[4]; /* 1-bit output of each channel, pre-volume */ INT32 Output[4]; /* 1-bit output of each channel, pre-volume */
INT32 CyclestoREADY;/* number of cycles until the READY line goes active */ INT32 CyclestoREADY;/* number of cycles until the READY line goes active */
INT32 Freq0IsMax; /* flag for if frequency zero acts as if it is one more than max (0x3ff+1) or if it acts like 0 */
}; };
@ -200,8 +213,9 @@ WRITE8_DEVICE_HANDLER( sn76496_w )
case 2: /* tone 1 : frequency */ case 2: /* tone 1 : frequency */
case 4: /* tone 2 : frequency */ case 4: /* tone 2 : frequency */
if ((data & 0x80) == 0) R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4); if ((data & 0x80) == 0) R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);
if (R->Register[r] != 0) R->Period[c] = R->Register[r]; if ((R->Register[r] != 0) || (R->Freq0IsMax == 0)) R->Period[c] = R->Register[r];
else R->Period[c] = 0x400; else R->Period[c] = 0x400;
if (r == 4) if (r == 4)
{ {
/* update noise shift frequency */ /* update noise shift frequency */
@ -371,6 +385,7 @@ static int SN76496_init(device_t *device, sn76496_state *R, int stereo)
R->Stereo = stereo; /* depends on init */ R->Stereo = stereo; /* depends on init */
R->CyclestoREADY = 1; /* assume ready is not active immediately on init. is this correct?*/ R->CyclestoREADY = 1; /* assume ready is not active immediately on init. is this correct?*/
R->StereoMask = 0xFF; /* all channels enabled */ R->StereoMask = 0xFF; /* all channels enabled */
R->Freq0IsMax = 1; /* frequency set to 0 results in freq = 0x400 rather than 0 */
R->RNG = R->FeedbackMask; R->RNG = R->FeedbackMask;
R->Output[3] = R->RNG & 1; R->Output[3] = R->RNG & 1;
@ -379,7 +394,7 @@ static int SN76496_init(device_t *device, sn76496_state *R, int stereo)
} }
static void generic_start(device_t *device, int feedbackmask, int noisetap1, int noisetap2, int negate, int stereo, int clockdivider) static void generic_start(device_t *device, int feedbackmask, int noisetap1, int noisetap2, int negate, int stereo, int clockdivider, int freq0)
{ {
sn76496_state *chip = get_safe_token(device); sn76496_state *chip = get_safe_token(device);
@ -394,6 +409,7 @@ static void generic_start(device_t *device, int feedbackmask, int noisetap1, int
chip->Stereo = stereo; chip->Stereo = stereo;
chip->ClockDivider = clockdivider; chip->ClockDivider = clockdivider;
chip->CurrentClock = clockdivider-1; chip->CurrentClock = clockdivider-1;
chip->Freq0IsMax = freq0;
device->save_item(NAME(chip->VolTable)); device->save_item(NAME(chip->VolTable));
device->save_item(NAME(chip->Register)); device->save_item(NAME(chip->Register));
@ -412,6 +428,7 @@ static void generic_start(device_t *device, int feedbackmask, int noisetap1, int
device->save_item(NAME(chip->Count)); device->save_item(NAME(chip->Count));
device->save_item(NAME(chip->Output)); device->save_item(NAME(chip->Output));
device->save_item(NAME(chip->CyclestoREADY)); device->save_item(NAME(chip->CyclestoREADY));
device->save_item(NAME(chip->Freq0IsMax));
} }
// function parameters: device, feedback destination tap, feedback source taps, // function parameters: device, feedback destination tap, feedback source taps,
@ -419,42 +436,42 @@ static void generic_start(device_t *device, int feedbackmask, int noisetap1, int
static DEVICE_START( sn76489 ) static DEVICE_START( sn76489 )
{ {
generic_start(device, 0x4000, 0x01, 0x02, TRUE, FALSE, 8); // SN76489 not verified yet. todo: verify; generic_start(device, 0x4000, 0x01, 0x02, TRUE, FALSE, 8, TRUE); // SN76489 not verified yet. todo: verify;
} }
static DEVICE_START( sn76489a ) static DEVICE_START( sn76489a )
{ {
generic_start(device, 0x10000, 0x04, 0x08, FALSE, FALSE, 8); // SN76489A: whitenoise verified, phase verified, periodic verified (by plgdavid) generic_start(device, 0x10000, 0x04, 0x08, FALSE, FALSE, 8, TRUE); // SN76489A: whitenoise verified, phase verified, periodic verified (by plgdavid)
} }
static DEVICE_START( sn76494 ) static DEVICE_START( sn76494 )
{ {
generic_start(device, 0x10000, 0x04, 0x08, FALSE, FALSE, 1); // SN76494 not verified, (according to datasheet: same as sn76489a but without the /8 divider) generic_start(device, 0x10000, 0x04, 0x08, FALSE, FALSE, 1, TRUE); // SN76494 not verified, (according to datasheet: same as sn76489a but without the /8 divider)
} }
static DEVICE_START( sn76496 ) static DEVICE_START( sn76496 )
{ {
generic_start(device, 0x10000, 0x04, 0x08, FALSE, FALSE, 8); // SN76496: Whitenoise verified, phase verified, periodic verified (by Michael Zapf) generic_start(device, 0x10000, 0x04, 0x08, FALSE, FALSE, 8, TRUE); // SN76496: Whitenoise verified, phase verified, periodic verified (by Michael Zapf)
} }
static DEVICE_START( sn94624 ) static DEVICE_START( sn94624 )
{ {
generic_start(device, 0x4000, 0x01, 0x02, TRUE, FALSE, 1); // SN94624 whitenoise verified, phase verified, period verified; verified by PlgDavid generic_start(device, 0x4000, 0x01, 0x02, TRUE, FALSE, 1, TRUE); // SN94624 whitenoise verified, phase verified, period verified; verified by PlgDavid
} }
static DEVICE_START( ncr7496 ) static DEVICE_START( ncr7496 )
{ {
generic_start(device, 0x8000, 0x02, 0x20, FALSE, FALSE, 8); // NCR7496 not verified; info from smspower wiki generic_start(device, 0x8000, 0x02, 0x20, FALSE, FALSE, 8, TRUE); // NCR7496 not verified; info from smspower wiki
} }
static DEVICE_START( gamegear ) static DEVICE_START( gamegear )
{ {
generic_start(device, 0x8000, 0x01, 0x08, TRUE, TRUE, 8); // Verified by Justin Kerk generic_start(device, 0x8000, 0x01, 0x08, TRUE, TRUE, 8, FALSE); // Verified by Justin Kerk
} }
static DEVICE_START( smsiii ) static DEVICE_START( smsiii )
{ {
generic_start(device, 0x8000, 0x01, 0x08, TRUE, FALSE, 8); // todo: verify; from smspower wiki, assumed to have same invert as gamegear generic_start(device, 0x8000, 0x01, 0x08, TRUE, FALSE, 8, FALSE); // todo: verify; from smspower wiki, assumed to have same invert as gamegear
} }