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Add READY line readback, cleaned up struct a bit, cleaned up comments, added more TODOs, Fixed some unsaved savestate related stuff.

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This commit is contained in:
Jonathan Gevaryahu 2009-04-29 04:31:25 +00:00
parent 4240bd3abf
commit efd44dee47
2 changed files with 64 additions and 35 deletions
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98
src/emu/sound/sn76496.c
View File

@ -32,10 +32,24 @@
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.
TODO: Implement a function for setting stereo regs for the game gear.
Requires either making the entire core stereo and forcing mono out for all
chips except gamegear, or somehow making the core support both output typesf.
TODO: * Implement a function for setting stereo regs for the game gear.
Requires making the core support both mono and stereo, and have
a select register which determines which channels go where.
* Implement the TMS9919 and SN94624, which are earlier versions,
possibly lacking the /8 clock divider, of the SN76489, and hence
would have a max clock of 500Khz and 4 clocks per sample, as
opposed to max of 4Mhz and 32 clocks per sample on the SN76489A
* Implement the T6W28; has registers in a weird order, needs writes
to be 'sanitized' first. Also is stereo, similar to game gear.
* Implement the NCR 7496; Is probably 100% compatible with SN76496,
but the whitenoise taps could be different. Needs someone with a
Tandy 1200 or whatever it was which uses this to run some tests.
* Factor out common code so that the SAA1099 can share some code.
***************************************************************************/
#include "sndintrf.h"
@ -44,26 +58,26 @@
#define MAX_OUTPUT 0x7fff
#define STEP 0x10000
#define NOISEMODE (R->Register[6]&4)?1:0
typedef struct _sn76496_state sn76496_state;
struct _sn76496_state
{
sound_stream * Channel;
int SampleRate;
int VolTable[16]; /* volume table */
INT32 VolTable[16]; /* volume table (for 4-bit to db conversion)*/
INT32 Register[8]; /* registers */
INT32 LastRegister; /* last register written */
INT32 Volume[4]; /* volume of voice 0-2 and noise */
UINT32 RNG; /* noise generator */
INT32 NoiseMode; /* active noise mode */
INT32 FeedbackMask; /* mask for feedback */
INT32 WhitenoiseTaps; /* mask for white noise taps */
INT32 WhitenoiseInvert; /* white noise invert flag */
INT32 Period[4];
INT32 Count[4];
INT32 Output[4];
INT32 Volume[4]; /* db volume of voice 0-2 and noise */
UINT32 RNG; /* noise generator LFSR*/
INT32 FeedbackMask; /* mask for feedback */
INT32 WhitenoiseTaps; /* mask for white noise taps */
INT32 WhitenoiseInvert; /* white noise invert flag */
INT32 Period[4]; /* Length of 1/2 of waveform */
INT32 Count[4]; /* Position within the waveform */
INT32 Output[4]; /* 1-bit output of each channel, pre-volume */
INT32 CyclestoREADY;/* number of cycles until the READY line goes active */
};
@ -81,6 +95,12 @@ INLINE sn76496_state *get_safe_token(const device_config *device)
return (sn76496_state *)device->token;
}
READ8_DEVICE_HANDLER( sn76496_ready_r )
{
sn76496_state *R = get_safe_token(device);
stream_update(R->Channel);
return (R->CyclestoREADY? 0 : 1);
}
WRITE8_DEVICE_HANDLER( sn76496_w )
{
@ -91,6 +111,9 @@ WRITE8_DEVICE_HANDLER( sn76496_w )
/* update the output buffer before changing the registers */
stream_update(R->Channel);
/* set number of cycles until READY is active; this is always one 'sample', i.e. it equals the clock divider exactly; until the clock divider is fully supported, we delay until one sample has played */
R->CyclestoREADY = 1;
if (data & 0x80)
{
r = (data & 0x70) >> 4;
@ -128,12 +151,10 @@ WRITE8_DEVICE_HANDLER( sn76496_w )
{
if ((data & 0x80) == 0) R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
n = R->Register[6];
R->NoiseMode = (n & 4) ? 1 : 0;
/* N/512,N/1024,N/2048,Tone #3 output */
R->Period[3] = ((n&3) == 3) ? 2 * R->Period[2] : (STEP << (5+(n&3)));
/* Reset noise shifter */
R->RNG = R->FeedbackMask; /* this is correct according to the smspower document */
//R->RNG = 0xF35; /* this is not, but sounds better in do run run */
R->RNG = R->FeedbackMask;
R->Output[3] = R->RNG & 1;
}
break;
@ -149,14 +170,16 @@ static STREAM_UPDATE( SN76496Update )
stream_sample_t *buffer = outputs[0];
/* If the volume is 0, increase the counter */
/* If the volume is 0, increase the counter; this is more or less
a speedup hack for when silence is to be output */
for (i = 0;i < 4;i++)
{
if (R->Volume[i] == 0)
{
/* note that I do count += samples, NOT count = samples + 1. You might think */
/* it's the same since the volume is 0, but doing the latter could cause */
/* interferencies when the program is rapidly modulating the volume. */
/* note that I do count += samples, NOT count = samples + 1.
You might think it's the same since the volume is 0, but doing
the latter could cause interferencies when the program is
rapidly modulating the volume. */
if (R->Count[i] <= samples*STEP) R->Count[i] += samples*STEP;
}
}
@ -166,7 +189,9 @@ static STREAM_UPDATE( SN76496Update )
int vol[4];
unsigned int out;
int left;
/* decrement Cycles to READY by one */
if (R->CyclestoREADY >0) R->CyclestoREADY--;
/* vol[] keeps track of how long each square wave stays */
/* in the 1 position during the sample period. */
@ -176,14 +201,14 @@ static STREAM_UPDATE( SN76496Update )
{
if (R->Output[i]) vol[i] += R->Count[i];
R->Count[i] -= STEP;
/* Period[i] is the half period of the square wave. Here, in each */
/* loop I add Period[i] twice, so that at the end of the loop the */
/* square wave is in the same status (0 or 1) it was at the start. */
/* vol[i] is also incremented by Period[i], since the wave has been 1 */
/* exactly half of the time, regardless of the initial position. */
/* If we exit the loop in the middle, Output[i] has to be inverted */
/* and vol[i] incremented only if the exit status of the square */
/* wave is 1. */
/* Period[i] is the half period of the square wave. Here, in each
loop I add Period[i] twice, so that at the end of the loop the
square wave is in the same status (0 or 1) it was at the start.
vol[i] is also incremented by Period[i], since the wave has been 1
exactly half of the time, regardless of the initial position.
If we exit the loop in the middle, Output[i] has to be inverted
and vol[i] incremented only if the exit status of the square
wave is 1. */
while (R->Count[i] <= 0)
{
R->Count[i] += R->Period[i];
@ -212,7 +237,7 @@ static STREAM_UPDATE( SN76496Update )
R->Count[3] -= nextevent;
if (R->Count[3] <= 0)
{
if (R->NoiseMode == 1) /* White Noise Mode */
if (NOISEMODE == 1) /* White Noise Mode */
{
if (((R->RNG & R->WhitenoiseTaps) != R->WhitenoiseTaps) && ((R->RNG & R->WhitenoiseTaps) != 0)) /* crappy xor! */
{
@ -293,8 +318,6 @@ static int SN76496_init(const device_config *device, sn76496_state *R)
R->Channel = stream_create(device,0,1,sample_rate,R,SN76496Update);
R->SampleRate = sample_rate;
for (i = 0;i < 4;i++) R->Volume[i] = 0;
R->LastRegister = 0;
@ -314,6 +337,7 @@ static int SN76496_init(const device_config *device, sn76496_state *R)
R->FeedbackMask = 0x4000; /* mask for feedback */
R->WhitenoiseTaps = 0x03; /* mask for white noise taps */
R->WhitenoiseInvert = 1; /* white noise invert flag */
R->CyclestoREADY = 1; /* assume ready is not active immediately on init. is this correct?*/
R->RNG = R->FeedbackMask;
R->Output[3] = R->RNG & 1;
@ -334,14 +358,18 @@ static void generic_start(const device_config *device, int feedbackmask, int noi
chip->WhitenoiseTaps = noisetaps;
chip->WhitenoiseInvert = noiseinvert;
state_save_register_device_item_array(device, 0, chip->VolTable);
state_save_register_device_item_array(device, 0, chip->Register);
state_save_register_device_item(device, 0, chip->LastRegister);
state_save_register_device_item_array(device, 0, chip->Volume);
state_save_register_device_item(device, 0, chip->RNG);
state_save_register_device_item(device, 0, chip->NoiseMode);
state_save_register_device_item(device, 0, chip->FeedbackMask);
state_save_register_device_item(device, 0, chip->WhitenoiseTaps);
state_save_register_device_item(device, 0, chip->WhitenoiseInvert);
state_save_register_device_item_array(device, 0, chip->Period);
state_save_register_device_item_array(device, 0, chip->Count);
state_save_register_device_item_array(device, 0, chip->Output);
state_save_register_device_item(device, 0, chip->CyclestoREADY);
}

1
src/emu/sound/sn76496.h
View File

@ -3,6 +3,7 @@
#ifndef __SN76496_H__
#define __SN76496_H__
READ8_DEVICE_HANDLER( sn76496_ready_r );
WRITE8_DEVICE_HANDLER( sn76496_w );
DEVICE_GET_INFO( sn76496 );