176 lines
4.2 KiB
C++
176 lines
4.2 KiB
C++
// license:BSD-3-Clause
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// copyright-holders:Acho A. Tang,R. Belmont, Valley Bell
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/*********************************************************
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Irem GA20 PCM Sound Chip
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80 pin QFP, label NANAO GA20 (Nanao Corporation was Irem's parent company)
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TODO:
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- It's not currently known whether this chip is stereo.
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- Is sample position base(regs 0,1) used while sample is playing, or
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latched at key on? We've always emulated it the latter way.
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gunforc2 seems to be the only game updating the address regs sometimes
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while a sample is playing, but it doesn't seem intentional.
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- What is the 2nd sample address for? Is it end(cut-off) address, or
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loop start address? Every game writes a value that's past sample end.
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- All games write either 0 or 2 to reg #6, do other bits have any function?
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Revisions:
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04-15-2002 Acho A. Tang
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- rewrote channel mixing
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- added prelimenary volume and sample rate emulation
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05-30-2002 Acho A. Tang
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- applied hyperbolic gain control to volume and used
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a musical-note style progression in sample rate
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calculation(still very inaccurate)
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02-18-2004 R. Belmont
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- sample rate calculation reverse-engineered.
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Thanks to Fujix, Yasuhiro Ogawa, the Guru, and Tormod
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for real PCB samples that made this possible.
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02-03-2007 R. Belmont
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- Cleaned up faux x86 assembly.
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09-25-2018 Valley Bell & co
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- rewrote channel update to make data 0 act as sample terminator
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DISCLAIMER
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- This file is modified for suitable in furnace.
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- modified by cam900
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*********************************************************/
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#include "iremga20.h"
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#include <string.h>
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//**************************************************************************
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// LIVE DEVICE
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//**************************************************************************
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//-------------------------------------------------
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// iremga20_device - constructor
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//-------------------------------------------------
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iremga20_device::iremga20_device(iremga20_intf &intf) :
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m_regs{0},
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m_channel{channel_def(), channel_def(), channel_def(), channel_def()},
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m_intf(intf)
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{
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}
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//-------------------------------------------------
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// device_reset - device-specific reset
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//-------------------------------------------------
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void iremga20_device::device_reset()
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{
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memset(m_regs, 0, 0x20 * sizeof(u8));
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for (int i = 0; i < 4; i++)
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{
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m_channel[i].rate = 0;
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m_channel[i].pos = 0;
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m_channel[i].counter = 0;
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m_channel[i].end = 0;
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m_channel[i].volume = 0;
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m_channel[i].play = false;
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}
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}
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//-------------------------------------------------
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// sound_stream_update - handle a stream update
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//-------------------------------------------------
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void iremga20_device::sound_stream_update(short** outputs, int len)
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{
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for (int i = 0; i < len; i++)
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{
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for (int j = 0; j < 4; j++)
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{
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s32 sampleout = 0;
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channel_def &ch = m_channel[j];
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if (ch.play)
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{
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int sample = m_intf.read_byte(ch.pos);
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if (sample == 0x00) // check for sample end marker
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ch.play = false;
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else
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{
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sampleout = (sample - 0x80) * (s32)ch.volume;
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ch.counter--;
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if (ch.counter <= ch.rate)
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{
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ch.pos++;
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ch.counter = 0x100;
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}
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}
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}
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outputs[j][i] = sampleout;
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}
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}
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}
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void iremga20_device::write(u32 offset, u8 data)
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{
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offset &= 0x1f;
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m_regs[offset] = data;
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int ch = offset >> 3;
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// channel regs:
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// 0,1: start address
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// 2,3: end? address
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// 4: rate
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// 5: volume
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// 6: control
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// 7: voice status (read-only)
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switch (offset & 0x7)
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{
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case 4:
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m_channel[ch].rate = data;
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break;
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case 5:
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m_channel[ch].volume = (data * 256) / (data + 10);
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break;
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case 6:
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// d1: key on/off
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if (data & 2)
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{
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m_channel[ch].play = true;
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m_channel[ch].pos = (m_regs[ch << 3 | 0] | m_regs[ch << 3 | 1] << 8) << 4;
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m_channel[ch].end = (m_regs[ch << 3 | 2] | m_regs[ch << 3 | 3] << 8) << 4;
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m_channel[ch].counter = 0x100;
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}
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else
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m_channel[ch].play = false;
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// other: unknown/unused
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// possibilities are: loop flag, left/right speaker(stereo)
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break;
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}
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}
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u8 iremga20_device::read(u32 offset)
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{
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offset &= 0x1f;
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int ch = offset >> 3;
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switch (offset & 0x7)
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{
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case 7: // voice status. bit 0 is 1 if active. (routine around 0xccc in rtypeleo)
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return m_channel[ch].play ? 1 : 0;
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}
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return 0;
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}
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