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Diffstat (limited to 'src/devices/sound/t6w28.cpp')
-rw-r--r-- | src/devices/sound/t6w28.cpp | 356 |
1 files changed, 356 insertions, 0 deletions
diff --git a/src/devices/sound/t6w28.cpp b/src/devices/sound/t6w28.cpp new file mode 100644 index 00000000000..25303ec4f1b --- /dev/null +++ b/src/devices/sound/t6w28.cpp @@ -0,0 +1,356 @@ +// 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) +{ +} |