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add SN chip ported from MAME

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tildearrow 2021-05-14 03:23:12 -05:00
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// license:BSD-3-Clause
// copyright-holders:Nicola Salmoria
/***************************************************************************
sn76496.c
by Nicola Salmoria
with contributions by others
Routines to emulate the:
Texas Instruments SN76489, SN76489A, SN76494/SN76496
( Also known as, or at least compatible with, the TMS9919 and SN94624.)
and the Sega 'PSG' used on the Master System, Game Gear, and Megadrive/Genesis
This chip is known as the Programmable Sound Generator, or PSG, and is a 4
channel sound generator, with three squarewave channels and a noise/arbitrary
duty cycle channel.
Noise emulation for all verified chips should be accurate:
** SN76489 uses a 15-bit shift register with taps on bits D and E, output on E,
XOR function.
It uses a 15-bit ring buffer for periodic noise/arbitrary duty cycle.
Its output is inverted.
** SN94624 is the same as SN76489 but lacks the /8 divider on its clock input.
** SN76489A uses a 15-bit shift register with taps on bits D and E, output on F,
XOR function.
It uses a 15-bit ring buffer for periodic noise/arbitrary duty cycle.
Its output is not inverted.
** 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 on pin 9 is
documented.
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
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
on bits C and F, output on F
It uses a 16-bit ring buffer for periodic noise/arbitrary duty cycle.
(whether it uses an XOR or XNOR needs to be verified, assumed XOR)
(whether output is inverted or not needs to be verified, assumed to be inverted)
** Sega Game Gear PSG is identical to the SMS3/MD/Genesis one except it has an
extra register for mapping which channels go to which speaker.
The register, connected to a z80 port, means:
for bits 7 6 5 4 3 2 1 0
L3 L2 L1 L0 R3 R2 R1 R0
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.
** NCR8496 (as used on the Tandy 1000TX) is similar to the SN76489 but with a
different noise LFSR pattern: taps on bits A and E, output on E, XNOR function
It uses a 15-bit ring buffer for periodic noise/arbitrary duty cycle.
Its output is inverted.
** PSSJ-3 (as used on the later Tandy 1000 series computers) is the same as the
NCR8496 with the exception that its output is not inverted.
28/03/2005 : Sebastien Chevalier
Update th SN76496Write func, according to SN76489 doc found on SMSPower.
- On write with 0x80 set to 0, when LastRegister is other then TONE,
the function is similar than update with 0x80 set to 1
23/04/2007 : Lord Nightmare
Major update, implement all three different noise generation algorithms and a
set_variant call to discern among them.
28/04/2009 : Lord Nightmare
Add READY line readback; cleaned up struct a bit. Cleaned up comments.
Add more TODOs. Fixed some unsaved savestate related stuff.
04/11/2009 : Lord Nightmare
Changed the way that the invert works (it now selects between XOR and XNOR
for the taps), and added R->OldNoise to simulate the extra 0 that is always
output before the noise LFSR contents are after an LFSR reset.
This fixes SN76489/A to match chips. Added SN94624.
14/11/2009 : Lord Nightmare
Removed STEP mess, vastly simplifying the code. Made output bipolar rather
than always above the 0 line, but disabled that code due to pending issues.
16/11/2009 : Lord Nightmare
Fix screeching in regulus: When summing together four equal channels, the
size of the max amplitude per channel should be 1/4 of the max range, not
1/3. Added NCR8496.
18/11/2009 : Lord Nightmare
Modify Init functions to support negating the audio output. The gamegear
psg does this. Change gamegear and sega psgs to use XOR rather than XNOR
based on testing. Got rid of R->OldNoise and fixed taps accordingly.
Added stereo support for game gear.
15/01/2010 : Lord Nightmare
Fix an issue with SN76489 and SN76489A having the wrong periodic noise periods.
Note that properly emulating the noise cycle bit timing accurately may require
extensive rewriting.
24/01/2010: Lord Nightmare
Implement periodic noise as forcing one of the XNOR or XOR taps to 1 or 0 respectively.
Thanks to PlgDavid for providing samples which helped immensely here.
Added true clock divider emulation, so sn94624 and sn76494 run 8x faster than
the others, as in real life.
15/02/2010: Lord Nightmare & Michael Zapf (additional testing by PlgDavid)
Fix noise period when set to mirror channel 3 and channel 3 period is set to 0 (tested on hardware for noise, wave needs tests) - MZ
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.
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.
27/06/2012: Michael Zapf
Converted to modern device, legacy devices were gradually removed afterwards.
16/09/2015: Lord Nightmare
Fix PSG chips to have volume reg inited on reset to 0x0 based on tests by
ValleyBell. Made Sega PSG chips start up with register 0x3 selected (volume
for channel 2) based on hardware tests by Nemesis.
03/09/2018: Lord Nightmare, Qbix, ValleyBell, NewRisingSun
* renamed the NCR8496 to its correct name, based on chip pictures on VGMPF
* fixed NCR8496's noise LFSR behavior so it is only reset if the mode bit in
register 6 is changed.
* NCR8496's LFSR feedback function is an XNOR, which is now supported.
* add PSSJ-3 support for the later Tandy 1000 series computers.
* NCR8496's output is inverted, PSSJ-3's output is not.
10/12/2019: Michael Zapf
* READY line handling by own emu_timer, not depending on sound_stream_update
TODO: * Implement the TMS9919 - any difference to sn94624?
* Implement the T6W28; has registers in a weird order, needs writes
to be 'sanitized' first. Also is stereo, similar to game gear.
* Factor out common code so that the SAA1099 can share some code.
* verify NCR8496/PSSJ-3 behavior on write to mirrored registers; unlike the
other variants, the NCR-derived variants are implied to ignore writes to
regs 1,3,5,6,7 if 0x80 is not set. This needs to be verified on real hardware.
***************************************************************************/
#include "sn76496.h"
#include <stdio.h>
#define MAX_OUTPUT 0x7fff
sn76496_base_device::sn76496_base_device(
const char *tag,
int feedbackmask,
int noisetap1,
int noisetap2,
bool negate,
int clockdivider,
bool ncr,
bool sega,
uint32_t clock)
: m_feedback_mask(feedbackmask)
, m_whitenoise_tap1(noisetap1)
, m_whitenoise_tap2(noisetap2)
, m_clock_divider(clockdivider)
, m_ncr_style_psg(ncr)
, m_sega_style_psg(sega)
{
}
sn76496_device::sn76496_device(const char *tag, uint32_t clock)
: sn76496_base_device(tag, 0x10000, 0x04, 0x08, false, 8, false, true, clock)
{
}
void sn76496_base_device::device_start()
{
int i;
double out;
int gain;
for (i = 0; i < 4; i++) m_volume[i] = 0;
m_last_register = m_sega_style_psg?3:0; // Sega VDP PSG defaults to selected period reg for 2nd channel
for (i = 0; i < 8; i+=2)
{
m_register[i] = 0;
m_register[i + 1] = 0x0; // volume = 0x0 (max volume) on reset; this needs testing on chips other than SN76489A and Sega VDP PSG
}
for (i = 0; i < 4; i++)
{
m_output[i] = 0;
m_period[i] = 0;
m_count[i] = 0;
}
m_RNG = m_feedback_mask;
m_output[3] = m_RNG & 1;
m_current_clock = m_clock_divider-1;
// set gain
gain = 0;
gain &= 0xff;
// increase max output basing on gain (0.2 dB per step)
out = MAX_OUTPUT / 4; // four channels, each gets 1/4 of the total range
while (gain-- > 0)
out *= 1.023292992; // = (10 ^ (0.2/20))
// build volume table (2dB per step)
for (i = 0; i < 15; i++)
{
// limit volume to avoid clipping
if (out > MAX_OUTPUT / 4) m_vol_table[i] = MAX_OUTPUT / 4;
else m_vol_table[i] = out;
out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */
}
m_vol_table[15] = 0;
m_ready_state = true;
}
void sn76496_base_device::write(u8 data)
{
int n, r, c;
if (data & 0x80)
{
r = (data & 0x70) >> 4;
m_last_register = r;
if (((m_ncr_style_psg) && (r == 6)) && ((data&0x04) != (m_register[6]&0x04))) m_RNG = m_feedback_mask; // NCR-style PSG resets the LFSR only on a mode write which actually changes the state of bit 2 of register 6
m_register[r] = (m_register[r] & 0x3f0) | (data & 0x0f);
}
else
{
r = m_last_register;
//if ((m_ncr_style_psg) && ((r & 1) || (r == 6))) return; // NCR-style PSG ignores writes to regs 1, 3, 5, 6 and 7 with bit 7 clear; this behavior is not verified on hardware yet, uncomment it once verified.
}
c = r >> 1;
switch (r)
{
case 0: // tone 0: frequency
case 2: // tone 1: frequency
case 4: // tone 2: frequency
if ((data & 0x80) == 0) m_register[r] = (m_register[r] & 0x0f) | ((data & 0x3f) << 4);
if ((m_register[r] != 0) || (!m_sega_style_psg)) m_period[c] = m_register[r];
else m_period[c] = 0x400;
if (r == 4)
{
// update noise shift frequency
if ((m_register[6] & 0x03) == 0x03) m_period[3] = m_period[2]<<1;
}
break;
case 1: // tone 0: volume
case 3: // tone 1: volume
case 5: // tone 2: volume
case 7: // noise: volume
m_volume[c] = m_vol_table[data & 0x0f];
if ((data & 0x80) == 0) m_register[r] = (m_register[r] & 0x3f0) | (data & 0x0f);
break;
case 6: // noise: frequency, mode
{
if ((data & 0x80) == 0) printf("sn76496_base_device: write to reg 6 with bit 7 clear; data was %03x, new write is %02x! report this to LN!\n", m_register[6], data);
if ((data & 0x80) == 0) m_register[r] = (m_register[r] & 0x3f0) | (data & 0x0f);
n = m_register[6];
// N/512,N/1024,N/2048,Tone #3 output
m_period[3] = ((n&3) == 3)? (m_period[2]<<1) : (1 << (5+(n&3)));
if (!(m_ncr_style_psg)) m_RNG = m_feedback_mask;
}
break;
}
//m_ready_state = false;
}
inline bool sn76496_base_device::in_noise_mode()
{
return ((m_register[6] & 4)!=0);
}
void sn76496_base_device::sound_stream_update(short* outputs, int outLen)
{
int i;
int16_t out;
int16_t out2 = 0;
for (int sampindex = 0; sampindex < outLen; sampindex++)
{
// clock chip once
if (m_current_clock > 0) // not ready for new divided clock
{
m_current_clock--;
}
else // ready for new divided clock, make a new sample
{
m_current_clock = m_clock_divider-1;
// handle channels 0,1,2
for (i = 0; i < 3; i++)
{
m_count[i]--;
if (m_count[i] <= 0)
{
m_output[i] ^= 1;
m_count[i] = m_period[i];
}
}
// handle channel 3
m_count[3]--;
if (m_count[3] <= 0)
{
// if noisemode is 1, both taps are enabled
// if noisemode is 0, the lower tap, whitenoisetap2, is held at 0
// The != was a bit-XOR (^) before
if (((m_RNG & m_whitenoise_tap1)!=0) != (((int32_t)(m_RNG & m_whitenoise_tap2)!=(m_ncr_style_psg?m_whitenoise_tap2:0)) && in_noise_mode()))
{
m_RNG >>= 1;
m_RNG |= m_feedback_mask;
}
else
{
m_RNG >>= 1;
}
m_output[3] = m_RNG & 1;
m_count[3] = m_period[3];
}
}
out= ((m_output[0]!=0)? m_volume[0]:0)
+((m_output[1]!=0)? m_volume[1]:0)
+((m_output[2]!=0)? m_volume[2]:0)
+((m_output[3]!=0)? m_volume[3]:0);
if (m_negate) { out = -out; out2 = -out2; }
outputs[sampindex]=out;
}
}

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// license:BSD-3-Clause
// copyright-holders:Nicola Salmoria
// additional modifications by tildearrow to a
#ifndef MAME_SOUND_SN76496_H
#define MAME_SOUND_SN76496_H
#include <stdlib.h>
#include <stdint.h>
typedef unsigned char u8;
class sn76496_base_device {
public:
void stereo_w(u8 data);
void write(u8 data);
void device_start();
void sound_stream_update(short* outputs, int outLen);
//DECLARE_READ_LINE_MEMBER( ready_r ) { return m_ready_state ? 1 : 0; }
protected:
sn76496_base_device(
const char *tag,
int feedbackmask,
int noisetap1,
int noisetap2,
bool negate,
int clockdivider,
bool ncr,
bool sega,
uint32_t clock);
private:
inline bool in_noise_mode();
bool m_ready_state;
const int32_t m_feedback_mask; // mask for feedback
const int32_t m_whitenoise_tap1; // mask for white noise tap 1 (higher one, usually bit 14)
const int32_t m_whitenoise_tap2; // mask for white noise tap 2 (lower one, usually bit 13)
bool m_negate; // output negate flag
const int32_t m_clock_divider; // clock divider
const bool m_ncr_style_psg; // flag to ignore writes to regs 1,3,5,6,7 with bit 7 low
const bool m_sega_style_psg; // flag to make frequency zero acts as if it is one more than max (0x3ff+1) or if it acts like 0; the initial register is pointing to 0x3 instead of 0x0; the volume reg is preloaded with 0xF instead of 0x0
int32_t m_clock;
int32_t m_vol_table[16]; // volume table (for 4-bit to db conversion)
int32_t m_register[8]; // registers
int32_t m_last_register; // last register written
int32_t m_volume[4]; // db volume of voice 0-2 and noise
uint32_t m_RNG; // noise generator LFSR
int32_t m_current_clock;
int32_t m_period[4]; // Length of 1/2 of waveform
int32_t m_count[4]; // Position within the waveform
int32_t m_output[4]; // 1-bit output of each channel, pre-volume
};
// SN76496: Whitenoise verified, phase verified, periodic verified (by Michael Zapf)
class sn76496_device : public sn76496_base_device
{
public:
sn76496_device(const char *tag, uint32_t clock);
};
#endif // MAME_SOUND_SN76496_H