ay8910.c

著名ARC模拟器源码,包括多个平台

	{
		if (PSG->CountC <= length*STEP) PSG->CountC += length*STEP;
	}

	/* for the noise channel we must not touch OutputN - it's also not necessary */
	/* since we use outn. */
	if ((PSG->Regs[AY_ENABLE] & 0x38) == 0x38)	/* all off */
		if (PSG->CountN <= length*STEP) PSG->CountN += length*STEP;

	outn = (PSG->OutputN | PSG->Regs[AY_ENABLE]);


	/* buffering loop */
	while (length)
	{
		int vola,volb,volc;
		int left;


		/* vola, volb and volc keep track of how long each square wave stays */
		/* in the 1 position during the sample period. */
		vola = volb = volc = 0;

		left = STEP;
		do
		{
			int nextevent;


			if (PSG->CountN < left) nextevent = PSG->CountN;
			else nextevent = left;

			if (outn & 0x08)
			{
				if (PSG->OutputA) vola += PSG->CountA;
				PSG->CountA -= nextevent;
				/* PeriodA is the half period of the square wave. Here, in each */
				/* loop I add PeriodA 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. */
				/* vola is also incremented by PeriodA, since the wave has been 1 */
				/* exactly half of the time, regardless of the initial position. */
				/* If we exit the loop in the middle, OutputA has to be inverted */
				/* and vola incremented only if the exit status of the square */
				/* wave is 1. */
				while (PSG->CountA <= 0)
				{
					PSG->CountA += PSG->PeriodA;
					if (PSG->CountA > 0)
					{
						PSG->OutputA ^= 1;
						if (PSG->OutputA) vola += PSG->PeriodA;
						break;
					}
					PSG->CountA += PSG->PeriodA;
					vola += PSG->PeriodA;
				}
				if (PSG->OutputA) vola -= PSG->CountA;
			}
			else
			{
				PSG->CountA -= nextevent;
				while (PSG->CountA <= 0)
				{
					PSG->CountA += PSG->PeriodA;
					if (PSG->CountA > 0)
					{
						PSG->OutputA ^= 1;
						break;
					}
					PSG->CountA += PSG->PeriodA;
				}
			}

			if (outn & 0x10)
			{
				if (PSG->OutputB) volb += PSG->CountB;
				PSG->CountB -= nextevent;
				while (PSG->CountB <= 0)
				{
					PSG->CountB += PSG->PeriodB;
					if (PSG->CountB > 0)
					{
						PSG->OutputB ^= 1;
						if (PSG->OutputB) volb += PSG->PeriodB;
						break;
					}
					PSG->CountB += PSG->PeriodB;
					volb += PSG->PeriodB;
				}
				if (PSG->OutputB) volb -= PSG->CountB;
			}
			else
			{
				PSG->CountB -= nextevent;
				while (PSG->CountB <= 0)
				{
					PSG->CountB += PSG->PeriodB;
					if (PSG->CountB > 0)
					{
						PSG->OutputB ^= 1;
						break;
					}
					PSG->CountB += PSG->PeriodB;
				}
			}

			if (outn & 0x20)
			{
				if (PSG->OutputC) volc += PSG->CountC;
				PSG->CountC -= nextevent;
				while (PSG->CountC <= 0)
				{
					PSG->CountC += PSG->PeriodC;
					if (PSG->CountC > 0)
					{
						PSG->OutputC ^= 1;
						if (PSG->OutputC) volc += PSG->PeriodC;
						break;
					}
					PSG->CountC += PSG->PeriodC;
					volc += PSG->PeriodC;
				}
				if (PSG->OutputC) volc -= PSG->CountC;
			}
			else
			{
				PSG->CountC -= nextevent;
				while (PSG->CountC <= 0)
				{
					PSG->CountC += PSG->PeriodC;
					if (PSG->CountC > 0)
					{
						PSG->OutputC ^= 1;
						break;
					}
					PSG->CountC += PSG->PeriodC;
				}
			}

			PSG->CountN -= nextevent;
			if (PSG->CountN <= 0)
			{
				/* Is noise output going to change? */
				if ((PSG->RNG + 1) & 2)	/* (bit0^bit1)? */
				{
					PSG->OutputN = ~PSG->OutputN;
					outn = (PSG->OutputN | PSG->Regs[AY_ENABLE]);
				}

				/* The Random Number Generator of the 8910 is a 17-bit shift */
				/* register. The input to the shift register is bit0 XOR bit2 */
				/* (bit0 is the output). */

				/* The following is a fast way to compute bit 17 = bit0^bit2. */
				/* Instead of doing all the logic operations, we only check */
				/* bit 0, relying on the fact that after two shifts of the */
				/* register, what now is bit 2 will become bit 0, and will */
				/* invert, if necessary, bit 16, which previously was bit 18. */
				if (PSG->RNG & 1) PSG->RNG ^= 0x28000;
				PSG->RNG >>= 1;
				PSG->CountN += PSG->PeriodN;
			}

			left -= nextevent;
		} while (left > 0);

		/* update envelope */
		if (PSG->Holding == 0)
		{
			PSG->CountE -= STEP;
			if (PSG->CountE <= 0)
			{
				do
				{
					PSG->CountEnv--;
					PSG->CountE += PSG->PeriodE;
				} while (PSG->CountE <= 0);

				/* check envelope current position */
				if (PSG->CountEnv < 0)
				{
					if (PSG->Hold)
					{
						if (PSG->Alternate)
							PSG->Attack ^= 0x1f;
						PSG->Holding = 1;
						PSG->CountEnv = 0;
					}
					else
					{
						/* if CountEnv has looped an odd number of times (usually 1), */
						/* invert the output. */
						if (PSG->Alternate && (PSG->CountEnv & 0x20))
 							PSG->Attack ^= 0x1f;

						PSG->CountEnv &= 0x1f;
					}
				}

				PSG->VolE = PSG->VolTable[PSG->CountEnv ^ PSG->Attack];
				/* reload volume */
				if (PSG->EnvelopeA) PSG->VolA = PSG->VolE;
				if (PSG->EnvelopeB) PSG->VolB = PSG->VolE;
				if (PSG->EnvelopeC) PSG->VolC = PSG->VolE;
			}
		}

		*(buf1++) = (vola * PSG->VolA) / STEP;
		*(buf2++) = (volb * PSG->VolB) / STEP;
		*(buf3++) = (volc * PSG->VolC) / STEP;

		length--;
	}
}


void AY8910_set_clock(int chip,int clock)
{
	struct AY8910 *PSG = &AYPSG[chip];

	/* the step clock for the tone and noise generators is the chip clock    */
	/* divided by 8; for the envelope generator of the AY-3-8910, it is half */
	/* that much (clock/16), but the envelope of the YM2149 goes twice as    */
	/* fast, therefore again clock/8.                                        */
	/* Here we calculate the number of steps which happen during one sample  */
	/* at the given sample rate. No. of events = sample rate / (clock/8).    */
	/* STEP is a multiplier used to turn the fraction into a fixed point     */
	/* number.                                                               */
	PSG->UpdateStep = (unsigned int)(((double)STEP * PSG->SampleRate * 8) / clock);
}


void AY8910_set_volume(int chip,int channel,int volume)
{
	struct AY8910 *PSG = &AYPSG[chip];
	int ch;

	for (ch = 0; ch < 3; ch++)
		if (channel == ch || channel == ALL_8910_CHANNELS)
			stream_set_volume(PSG->Channel + ch, volume);
}


static void build_mixer_table(int chip)
{
	struct AY8910 *PSG = &AYPSG[chip];
	int i;
	double out;


	/* calculate the volume->voltage conversion table */
	/* The AY-3-8910 has 16 levels, in a logarithmic scale (3dB per step) */
	/* The YM2149 still has 16 levels for the tone generators, but 32 for */
	/* the envelope generator (1.5dB per step). */
	out = MAX_OUTPUT;
	for (i = 31;i > 0;i--)
	{
		PSG->VolTable[i] = (unsigned int)(out + 0.5);	/* round to nearest */

		out /= 1.188502227;	/* = 10 ^ (1.5/20) = 1.5dB */
	}
	PSG->VolTable[0] = 0;
}



void AY8910_reset(int chip)
{
	int i;
	struct AY8910 *PSG = &AYPSG[chip];


	PSG->register_latch = 0;
	PSG->RNG = 1;
	PSG->OutputA = 0;
	PSG->OutputB = 0;
	PSG->OutputC = 0;
	PSG->OutputN = 0xff;
	for (i = 0;i < AY_PORTA;i++)
		_AYWriteReg(chip,i,0);	/* AYWriteReg() uses the timer system; we cannot */
								/* call it at this time because the timer system */
								/* has not been initialized. */
}

static int AY8910_init(const char *myname,int chip,
		int clock,int volume,int sample_rate,
		mem_read_handler portAread,mem_read_handler portBread,
		mem_write_handler portAwrite,mem_write_handler portBwrite)
{
	int i;
	struct AY8910 *PSG = &AYPSG[chip];
	char buf[3][40];
	const char *name[3];
	int vol[3];


	memset(PSG,0,sizeof(struct AY8910));
	PSG->SampleRate = sample_rate;
	PSG->PortAread = portAread;
	PSG->PortBread = portBread;
	PSG->PortAwrite = portAwrite;
	PSG->PortBwrite = portBwrite;
	for (i = 0;i < 3;i++)
	{
		vol[i] = volume;
		name[i] = buf[i];
		sprintf(buf[i],"%s #%d Ch %c",myname,chip,'A'+i);
	}
	PSG->Channel = stream_init_multi(3,name,sample_rate,16,chip,AY8910Update);
	for (i=0; i<3; i++) {
	  stream_set_volume(PSG->Channel+i,vol[i]);
	  stream_set_pan(PSG->Channel+i,0x80);
	}
	
	if (PSG->Channel == -1)
		return 1;

	AY8910_set_clock(chip,clock);
	AY8910_reset(chip);

	return 0;
}



int AY8910_sh_start_ex(const struct AY8910interface *intf,const char *name)
{
	int chip;

	for (chip = 0;chip < intf->num;chip++)
	{
		if (AY8910_init("AY8910",chip,intf->baseclock,
				intf->mixing_level[chip] & 0xffff,
				audio_sample_rate,
				intf->portAread[chip],intf->portBread[chip],
				intf->portAwrite[chip],intf->portBwrite[chip]) != 0)
			return 1;
		build_mixer_table(chip);
	}
	return 0;
}

int AY8910_sh_start(const struct AY8910interface *interface)
{
        return AY8910_sh_start_ex(interface,"AY8910");
}

int AY8910_get_stream_num( int chip ){
  struct AY8910 *PSG = &AYPSG[chip];
  return PSG->Channel;
}