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+// license:BSD-3-Clause
+// copyright-holders:Wilbert Pol
+/***************************************************************************
+
+ t6w28.c (based on sn74696.c)
+
+ The t6w28 sound core is used in the SNK NeoGeo Pocket. It is a stereo
+ sound chip based on 2 partial sn76489a cores.
+
+ The block diagram for this chip is as follows:
+
+Offset 0:
+ Tone 0 /----------> Att0 ---\
+ | |
+ Tone 1 | /-------> Att1 ---+
+ | | | Right
+ Tone 2 | | /----> Att2 ---+-------->
+ | | | | |
+ Noise -----+-------------> Att3 ---/
+ | | | |
+ | | | |
+ Offset 1: | | | |
+ Tone 0 --------+----------> Att0 ---\
+ | | | |
+ Tone 1 -----------+-------> Att1 ---+
+ | | | Left
+ Tone 2 --------------+----> Att2 ---+-------->
+ | |
+ Noise \-------------> Att3 ---/
+
+
+***************************************************************************/
+
+#include "emu.h"
+#include "t6w28.h"
+
+
+#define MAX_OUTPUT 0x7fff
+
+#define STEP 0x10000
+
+WRITE8_MEMBER( t6w28_device::write )
+{
+ int n, r, c;
+
+
+ /* update the output buffer before changing the registers */
+ m_channel->update();
+
+ offset &= 1;
+
+ if (data & 0x80)
+ {
+ r = (data & 0x70) >> 4;
+ m_last_register[offset] = r;
+ m_register[offset * 8 + r] = (m_register[offset * 8 + r] & 0x3f0) | (data & 0x0f);
+ }
+ else
+ {
+ r = m_last_register[offset];
+ }
+ c = r/2;
+ switch (r)
+ {
+ case 0: /* tone 0 : frequency */
+ case 2: /* tone 1 : frequency */
+ case 4: /* tone 2 : frequency */
+ if ((data & 0x80) == 0) m_register[offset * 8 + r] = (m_register[offset * 8 + r] & 0x0f) | ((data & 0x3f) << 4);
+ m_period[offset * 4 + c] = STEP * m_register[offset * 8 + r];
+ if (m_period[offset * 4 + c] == 0) m_period[offset * 4 + c] = STEP;
+ if (r == 4)
+ {
+ /* update noise shift frequency */
+ if ((m_register[offset * 8 + 6] & 0x03) == 0x03)
+ m_period[offset * 4 + 3] = 2 * m_period[offset * 4 + 2];
+ }
+ break;
+ case 1: /* tone 0 : volume */
+ case 3: /* tone 1 : volume */
+ case 5: /* tone 2 : volume */
+ case 7: /* noise : volume */
+ m_volume[offset * 4 + c] = m_vol_table[data & 0x0f];
+ if ((data & 0x80) == 0) m_register[offset * 8 + r] = (m_register[offset * 8 + r] & 0x3f0) | (data & 0x0f);
+ break;
+ case 6: /* noise : frequency, mode */
+ {
+ if ((data & 0x80) == 0) m_register[offset * 8 + r] = (m_register[offset * 8 + r] & 0x3f0) | (data & 0x0f);
+ n = m_register[offset * 8 + 6];
+ m_noise_mode[offset] = (n & 4) ? 1 : 0;
+ /* N/512,N/1024,N/2048,Tone #3 output */
+ m_period[offset * 4 + 3] = ((n&3) == 3) ? 2 * m_period[offset * 4 + 2] : (STEP << (5+(n&3)));
+ /* Reset noise shifter */
+ m_rng[offset] = m_feedback_mask; /* this is correct according to the smspower document */
+ //m_rng = 0xF35; /* this is not, but sounds better in do run run */
+ m_output[offset * 4 + 3] = m_rng[offset] & 1;
+ }
+ break;
+ }
+}
+
+
+
+//-------------------------------------------------
+// sound_stream_update - handle a stream update
+//-------------------------------------------------
+
+void t6w28_device::sound_stream_update(sound_stream &stream, stream_sample_t **inputs, stream_sample_t **outputs, int samples)
+{
+ int i;
+ stream_sample_t *buffer0 = outputs[0];
+ stream_sample_t *buffer1 = outputs[1];
+
+
+ /* If the volume is 0, increase the counter */
+ for (i = 0;i < 8;i++)
+ {
+ if (m_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. */
+ if (m_count[i] <= samples*STEP) m_count[i] += samples*STEP;
+ }
+ }
+
+ while (samples > 0)
+ {
+ int vol[8];
+ unsigned int out0, out1;
+ int left;
+
+
+ /* vol[] keeps track of how long each square wave stays */
+ /* in the 1 position during the sample period. */
+ vol[0] = vol[1] = vol[2] = vol[3] = vol[4] = vol[5] = vol[6] = vol[7] = 0;
+
+ for (i = 2;i < 3;i++)
+ {
+ if (m_output[i]) vol[i] += m_count[i];
+ m_count[i] -= STEP;
+ /* m_period[i] is the half period of the square wave. Here, in each */
+ /* loop I add m_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 m_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, m_output[i] has to be inverted */
+ /* and vol[i] incremented only if the exit status of the square */
+ /* wave is 1. */
+ while (m_count[i] <= 0)
+ {
+ m_count[i] += m_period[i];
+ if (m_count[i] > 0)
+ {
+ m_output[i] ^= 1;
+ if (m_output[i]) vol[i] += m_period[i];
+ break;
+ }
+ m_count[i] += m_period[i];
+ vol[i] += m_period[i];
+ }
+ if (m_output[i]) vol[i] -= m_count[i];
+ }
+
+ for (i = 4;i < 7;i++)
+ {
+ if (m_output[i]) vol[i] += m_count[i];
+ m_count[i] -= STEP;
+ /* m_period[i] is the half period of the square wave. Here, in each */
+ /* loop I add m_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 m_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, m_output[i] has to be inverted */
+ /* and vol[i] incremented only if the exit status of the square */
+ /* wave is 1. */
+ while (m_count[i] <= 0)
+ {
+ m_count[i] += m_period[i];
+ if (m_count[i] > 0)
+ {
+ m_output[i] ^= 1;
+ if (m_output[i]) vol[i] += m_period[i];
+ break;
+ }
+ m_count[i] += m_period[i];
+ vol[i] += m_period[i];
+ }
+ if (m_output[i]) vol[i] -= m_count[i];
+ }
+
+ left = STEP;
+ do
+ {
+ int nextevent;
+
+
+ if (m_count[3] < left) nextevent = m_count[3];
+ else nextevent = left;
+
+ if (m_output[3]) vol[3] += m_count[3];
+ m_count[3] -= nextevent;
+ if (m_count[3] <= 0)
+ {
+ if (m_noise_mode[0] == 1) /* White Noise Mode */
+ {
+ if (((m_rng[0] & m_whitenoise_taps) != m_whitenoise_taps) && ((m_rng[0] & m_whitenoise_taps) != 0)) /* crappy xor! */
+ {
+ m_rng[0] >>= 1;
+ m_rng[0] |= m_feedback_mask;
+ }
+ else
+ {
+ m_rng[0] >>= 1;
+ }
+ m_output[3] = m_whitenoise_invert ? !(m_rng[0] & 1) : m_rng[0] & 1;
+ }
+ else /* Periodic noise mode */
+ {
+ if (m_rng[0] & 1)
+ {
+ m_rng[0] >>= 1;
+ m_rng[0] |= m_feedback_mask;
+ }
+ else
+ {
+ m_rng[0] >>= 1;
+ }
+ m_output[3] = m_rng[0] & 1;
+ }
+ m_count[3] += m_period[3];
+ if (m_output[3]) vol[3] += m_period[3];
+ }
+ if (m_output[3]) vol[3] -= m_count[3];
+
+ left -= nextevent;
+ } while (left > 0);
+
+ if (m_enabled)
+ {
+ out0 = vol[4] * m_volume[4] + vol[5] * m_volume[5] +
+ vol[6] * m_volume[6] + vol[3] * m_volume[7];
+
+ out1 = vol[4] * m_volume[0] + vol[5] * m_volume[1] +
+ vol[6] * m_volume[2] + vol[3] * m_volume[3];
+ }
+ else
+ {
+ out0 = 0;
+ out1 = 0;
+ }
+
+ if (out0 > MAX_OUTPUT * STEP) out0 = MAX_OUTPUT * STEP;
+ if (out1 > MAX_OUTPUT * STEP) out1 = MAX_OUTPUT * STEP;
+
+ *(buffer0++) = out0 / STEP;
+ *(buffer1++) = out1 / STEP;
+
+ samples--;
+ }
+}
+
+
+
+void t6w28_device::set_gain(int gain)
+{
+ int i;
+ double out;
+
+ gain &= 0xff;
+
+ /* increase max output basing on gain (0.2 dB per step) */
+ out = MAX_OUTPUT / 3;
+ 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 / 3) m_vol_table[i] = MAX_OUTPUT / 3;
+ else m_vol_table[i] = out;
+
+ out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */
+ }
+ m_vol_table[15] = 0;
+}
+
+
+
+//-------------------------------------------------
+// device_start - device-specific startup
+//-------------------------------------------------
+
+void t6w28_device::device_start()
+{
+ int i;
+
+ m_sample_rate = clock() / 16;
+ m_channel = machine().sound().stream_alloc(*this, 0, 2, m_sample_rate);
+
+ for (i = 0;i < 8;i++) m_volume[i] = 0;
+
+ m_last_register[0] = 0;
+ m_last_register[1] = 0;
+ for (i = 0;i < 8;i+=2)
+ {
+ m_register[i] = 0;
+ m_register[i + 1] = 0x0f; /* volume = 0 */
+ }
+
+ for (i = 0;i < 8;i++)
+ {
+ m_output[i] = 0;
+ m_period[i] = m_count[i] = STEP;
+ }
+
+ /* Default is SN76489 non-A */
+ m_feedback_mask = 0x4000; /* mask for feedback */
+ m_whitenoise_taps = 0x03; /* mask for white noise taps */
+ m_whitenoise_invert = 1; /* white noise invert flag */
+
+ m_rng[0] = m_feedback_mask;
+ m_rng[1] = m_feedback_mask;
+ m_output[3] = m_rng[0] & 1;
+
+ set_gain(0);
+
+ /* values from sn76489a */
+ m_feedback_mask = 0x8000;
+ m_whitenoise_taps = 0x06;
+ m_whitenoise_invert = FALSE;
+
+ save_item(NAME(m_register));
+ save_item(NAME(m_last_register));
+ save_item(NAME(m_volume));
+ save_item(NAME(m_rng));
+ save_item(NAME(m_noise_mode));
+ save_item(NAME(m_period));
+ save_item(NAME(m_count));
+ save_item(NAME(m_output));
+ save_item(NAME(m_enabled));
+}
+
+
+void t6w28_device::set_enable(bool enable)
+{
+ m_enabled = enable;
+}
+
+const device_type T6W28 = &device_creator<t6w28_device>;
+
+t6w28_device::t6w28_device(const machine_config &mconfig, const char *tag, device_t *owner, UINT32 clock)
+ : device_t(mconfig, T6W28, "T6W28", tag, owner, clock, "t6w28", __FILE__),
+ device_sound_interface(mconfig, *this)
+{
+}