SCC.cc

Go to the documentation of this file.

//-----------------------------------------------------------------------------
//
// On Mon, 24 Feb 2003, Jon De Schrijder wrote:
//
// I've done some measurements with the scope on the output of the SCC.
// I didn't do timing tests, only amplitude checks:
//
// I know now for sure, the amplitude calculation works as follows:
//
// AmpOut=640+AmpA+AmpB+AmpC+AmpD+AmpE
//
// range AmpOut (11 bits positive number=SCC digital output): [+40...+1235]
//
// AmpA="((SampleValue*VolA) AND #7FF0) div 16"
// AmpB="((SampleValue*VolB) AND #7FF0) div 16"
// AmpC="((SampleValue*VolC) AND #7FF0) div 16"
// AmpD="((SampleValue*VolD) AND #7FF0) div 16"
// AmpE="((SampleValue*VolE) AND #7FF0) div 16"
//
// Setting the enablebit to zero, corresponds with VolX=0.
//
// SampleValue range [-128...+127]
// VolX range [0..15]
//
// Notes:
// * SampleValue*VolX is calculated (signed multiplication) and the lower 4
//   bits are dropped (both in case the value is positive or negative), before
//   the addition of the 5 values is done. This was tested by setting
//   SampleValue=+1 and VolX=15 of different channels. The resulting AmpOut=640,
//   indicating that the 4 lower bits were dropped *before* the addition.
//
//-----------------------------------------------------------------------------
//
// On Mon, 14 Apr 2003, Manuel Pazos wrote
//
// I have some info about SCC/SCC+ that I hope you find useful. It is about
// "Mode Setting Register", also called "Deformation Register" Here it goes:
//
//    bit0: 4 bits frequency (%XXXX00000000). Equivalent to
//          (normal frequency >> 8) bits0-7 are ignored
//    bit1: 8 bits frequency (%0000XXXXXXXX) bits8-11 are ignored
//    bit2:
//    bit3:
//    bit4:
//    bit5: wave data is played from begining when frequency is changed
//    bit6: rotate all waves data. You can't write to them. Rotation speed
//          =3.58Mhz / (channel i frequency + 1)
//    bit7: rotate channel 4 wave data. You can't write to that channel
//          data.ONLY works in MegaROM SCC (not in SCC+)
//
// If bit7 and bit6 are set, only channel 1-3 wave data rotates . You can't
// write to ANY wave data. And there is a weird behaviour in this setting. It
// seems SCC sound is corrupted in anyway with MSX databus or so. Try to
// activate them (with proper waves, freqs, and vol.) and execute DIR command
// on DOS. You will hear "noise" This seems to be fixed in SCC+
//
// Reading Mode Setting Register, is equivalent to write #FF to it.
//
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
//
// Additions:
//   - Setting both bit0 and bit1 is equivalent to setting only bit1
//   - A rotation goes like this:
//       wavedata[0:31] = wavedata[1:31].wavedata[0]
//   - Channel 4-5 rotation speed is set by channel 5 freq (channel 4 freq
//     is ignored for rotation)
//
// Also see this MRC thread:
//  http://www.msx.org/forumtopicl7875.html
//
//-----------------------------------------------------------------------------
//
// On Sat, 09 Sep 2005, NYYRIKKI wrote (MRC post)
//
// ...
//
// One important thing to know is that change of volume is not implemented
// immediately in SCC. Normally it is changed when next byte from sample memory
// is played, but writing value to frequency causes current byte to be started
// again. As in this example we write values very quickly to frequency registers
// the internal sample counter does not actually move at all.
//
// Third method is a variation of first method. As we don't know where SCC is
// playing, let's update the whole sample memory with one and same new value.
// To make sample rate not variable in low sample rates we first stop SCC from
// reading sample memory. This can be done by writing value less than 9 to
// frequency. Now we can update sample RAM so, that output does not change.
// After sample RAM has been updated, we start SCC internal counter so that
// value (where ever the counter was) is sent to output. This routine can be
// found below as example 3.
//
// ...
//
//
//
// Something completely different: the SCC+ is actually called SCC-I.
//-----------------------------------------------------------------------------
 
#include "SCC.hh"
#include "DeviceConfig.hh"
#include "cstd.hh"
#include "enumerate.hh"
#include "likely.hh"
#include "outer.hh"
#include "ranges.hh"
#include "serialize.hh"
#include "unreachable.hh"
#include "xrange.hh"
#include <cmath>
 
using std::string;
 
namespace openmsx {
 
static constexpr auto INPUT_RATE = unsigned(cstd::round(3579545.0 / 32));
 
static constexpr auto calcDescription(SCC::ChipMode mode)
{
        return (mode == SCC::SCC_Real) ? static_string_view("Konami SCC")
                                       : static_string_view("Konami SCC+");
}
 
SCC::SCC(const string& name_, const DeviceConfig& config,
         EmuTime::param time, ChipMode mode)
        : ResampledSoundDevice(
                config.getMotherBoard(), name_, calcDescription(mode), 5, INPUT_RATE, false)
        , debuggable(config.getMotherBoard(), getName())
        , deformTimer(time)
        , currentChipMode(mode)
{
        // Make valgrind happy
        ranges::fill(orgPeriod, 0);
 
        powerUp(time);
        registerSound(config);
}
 
SCC::~SCC()
{
        unregisterSound();
}
 
void SCC::powerUp(EmuTime::param time)
{
        // Power on values, tested by enen (log from IRC #openmsx):
        //
        //  <enen>    wouter_: i did an scc poweron values test, deform=0,
        //            amplitude=full, channelenable=0, period=under 8
        //    ...
        //  <wouter_> did you test the value of the waveforms as well?
        //    ...
        //  <enen>    filled with $FF, some bits cleared but that seems random
 
        // Initialize ch_enable, deform (initialize this before period)
        reset(time);
 
        // Initialize waveforms (initialize before volumes)
        for (auto& w1 : wave) {
                ranges::fill(w1, ~0);
        }
        // Initialize volume (initialize this before period)
        for (auto i : xrange(5)) {
                setFreqVol(i + 10, 15, time);
        }
        // Actual initial value is difficult to measure, assume zero
        // (initialize before period)
        ranges::fill(pos, 0);
 
        // Initialize period (sets members orgPeriod, period, incr, count, out)
        for (auto i : xrange(2 * 5)) {
                setFreqVol(i, 0, time);
        }
}
 
void SCC::reset(EmuTime::param /*time*/)
{
        if (currentChipMode != SCC_Real) {
                setChipMode(SCC_Compatible);
        }
 
        setDeformRegHelper(0);
        ch_enable = 0;
}
 
void SCC::setChipMode(ChipMode newMode)
{
        if (currentChipMode == SCC_Real) {
                assert(newMode == SCC_Real);
        } else {
                assert(newMode != SCC_Real);
        }
        currentChipMode = newMode;
}
 
byte SCC::readMem(byte addr, EmuTime::param time)
{
        // Deform-register locations:
        //   SCC_Real:       0xE0..0xFF
        //   SCC_Compatible: 0xC0..0xDF
        //   SCC_plusmode:   0xC0..0xDF
        if (((currentChipMode == SCC_Real) && (addr >= 0xE0)) ||
            ((currentChipMode != SCC_Real) && (0xC0 <= addr) && (addr < 0xE0))) {
                setDeformReg(0xFF, time);
        }
        return peekMem(addr, time);
}
 
byte SCC::peekMem(byte address, EmuTime::param time) const
{
        switch (currentChipMode) {
        case SCC_Real:
                if (address < 0x80) {
                        // 0x00..0x7F : read wave form 1..4
                        return readWave(address >> 5, address, time);
                } else {
                        // 0x80..0x9F : freq volume block, write only
                        // 0xA0..0xDF : no function
                        // 0xE0..0xFF : deformation register
                        return 0xFF;
                }
        case SCC_Compatible:
                if (address < 0x80) {
                        // 0x00..0x7F : read wave form 1..4
                        return readWave(address >> 5, address, time);
                } else if (address < 0xA0) {
                        // 0x80..0x9F : freq volume block
                        return 0xFF;
                } else if (address < 0xC0) {
                        // 0xA0..0xBF : read wave form 5
                        return readWave(4, address, time);
                } else {
                        // 0xC0..0xDF : deformation register
                        // 0xE0..0xFF : no function
                        return 0xFF;
                }
        case SCC_plusmode:
                if (address < 0xA0) {
                        // 0x00..0x9F : read wave form 1..5
                        return readWave(address >> 5, address, time);
                } else {
                        // 0xA0..0xBF : freq volume block
                        // 0xC0..0xDF : deformation register
                        // 0xE0..0xFF : no function
                        return 0xFF;
                }
        default:
                UNREACHABLE; return 0;
        }
}
 
byte SCC::readWave(unsigned channel, unsigned address, EmuTime::param time) const
{
        if (!rotate[channel]) {
                return wave[channel][address & 0x1F];
        } else {
                unsigned ticks = deformTimer.getTicksTill(time);
                unsigned periodCh = ((channel == 3) &&
                                     (currentChipMode != SCC_plusmode) &&
                                     ((deformValue & 0xC0) == 0x40))
                                  ? 4 : channel;
                unsigned shift = ticks / (period[periodCh] + 1);
                return wave[channel][(address + shift) & 0x1F];
        }
}
 
 
byte SCC::getFreqVol(unsigned address) const
{
        address &= 0x0F;
        if (address < 0x0A) {
                // get frequency
                unsigned channel = address / 2;
                if (address & 1) {
                        return orgPeriod[channel] >> 8;
                } else {
                        return orgPeriod[channel] & 0xFF;
                }
        } else if (address < 0x0F) {
                // get volume
                return volume[address - 0xA];
        } else {
                // get enable-bits
                return ch_enable;
        }
}
 
void SCC::writeMem(byte address, byte value, EmuTime::param time)
{
        updateStream(time);
 
        switch (currentChipMode) {
        case SCC_Real:
                if (address < 0x80) {
                        // 0x00..0x7F : write wave form 1..4
                        writeWave(address >> 5, address, value);
                } else if (address < 0xA0) {
                        // 0x80..0x9F : freq volume block
                        setFreqVol(address, value, time);
                } else if (address < 0xE0) {
                        // 0xA0..0xDF : no function
                } else {
                        // 0xE0..0xFF : deformation register
                        setDeformReg(value, time);
                }
                break;
        case SCC_Compatible:
                if (address < 0x80) {
                        // 0x00..0x7F : write wave form 1..4
                        writeWave(address >> 5, address, value);
                } else if (address < 0xA0) {
                        // 0x80..0x9F : freq volume block
                        setFreqVol(address, value, time);
                } else if (address < 0xC0) {
                        // 0xA0..0xBF : ignore write wave form 5
                } else if (address < 0xE0) {
                        // 0xC0..0xDF : deformation register
                        setDeformReg(value, time);
                } else {
                        // 0xE0..0xFF : no function
                }
                break;
        case SCC_plusmode:
                if (address < 0xA0) {
                        // 0x00..0x9F : write wave form 1..5
                        writeWave(address >> 5, address, value);
                } else if (address < 0xC0) {
                        // 0xA0..0xBF : freq volume block
                        setFreqVol(address, value, time);
                } else if (address < 0xE0) {
                        // 0xC0..0xDF : deformation register
                        setDeformReg(value, time);
                } else {
                        // 0xE0..0xFF : no function
                }
                break;
        default:
                UNREACHABLE;
        }
}
 
float SCC::getAmplificationFactorImpl() const
{
        return 1.0f / 128.0f;
}
 
static constexpr float adjust(signed char wav, byte vol)
{
        // The result is an integer value, but we store it as a float because
        // then we need fewer int->float conversion (compared to converting in
        // generateChannels()).
        return float((int(wav) * vol) >> 4);
}
 
void SCC::writeWave(unsigned channel, unsigned address, byte value)
{
        // write to channel 5 only possible in SCC+ mode
        assert(channel < 5);
        assert((channel != 4) || (currentChipMode == SCC_plusmode));
 
        if (!readOnly[channel]) {
                unsigned p = address & 0x1F;
                wave[channel][p] = value;
                volAdjustedWave[channel][p] = adjust(value, volume[channel]);
                if ((currentChipMode != SCC_plusmode) && (channel == 3)) {
                        // copy waveform 4 -> waveform 5
                        wave[4][p] = wave[3][p];
                        volAdjustedWave[4][p] = adjust(value, volume[4]);
                }
        }
}
 
void SCC::setFreqVol(unsigned address, byte value, EmuTime::param time)
{
        address &= 0x0F; // region is visible twice
        if (address < 0x0A) {
                // change frequency
                unsigned channel = address / 2;
                unsigned per =
                          (address & 1)
                        ? ((value & 0xF) << 8) | (orgPeriod[channel] & 0xFF)
                        : (orgPeriod[channel] & 0xF00) | (value & 0xFF);
                orgPeriod[channel] = per;
                if (deformValue & 2) {
                        // 8 bit frequency
                        per &= 0xFF;
                } else if (deformValue & 1) {
                        // 4 bit frequency
                        per >>= 8;
                }
                period[channel] = per;
                incr[channel] = (per <= 8) ? 0 : 32;
                count[channel] = 0; // reset to begin of byte
                if (deformValue & 0x20) {
                        pos[channel] = 0; // reset to begin of waveform
                        // also 'rotation' mode (confirmed by test based on
                        // Artag's SCC sample player)
                        deformTimer.advance(time);
                }
                // after a freq change, update the output
                out[channel] = volAdjustedWave[channel][pos[channel]];
        } else if (address < 0x0F) {
                // change volume
                unsigned channel = address - 0x0A;
                volume[channel] = value & 0xF;
                for (auto i : xrange(32)) {
                        volAdjustedWave[channel][i] =
                                adjust(wave[channel][i], volume[channel]);
                }
        } else {
                // change enable-bits
                ch_enable = value;
        }
}
 
void SCC::setDeformReg(byte value, EmuTime::param time)
{
        if (value == deformValue) {
                return;
        }
        deformTimer.advance(time);
        setDeformRegHelper(value);
}
 
void SCC::setDeformRegHelper(byte value)
{
        deformValue = value;
        if (currentChipMode != SCC_Real) {
                value &= ~0x80;
        }
        switch (value & 0xC0) {
        case 0x00:
                ranges::fill(rotate, false);
                ranges::fill(readOnly, false);
                break;
        case 0x40:
                ranges::fill(rotate, true);
                ranges::fill(readOnly, true);
                break;
        case 0x80:
                for (auto i : xrange(3)) {
                        rotate[i] = false;
                        readOnly[i] = false;
                }
                for (auto i : xrange(3, 5)) {
                        rotate[i] = true;
                        readOnly[i] = true;
                }
                break;
        case 0xC0:
                for (auto i : xrange(3)) {
                        rotate[i] = true;
                        readOnly[i] = true;
                }
                for (auto i : xrange(3, 5)) {
                        rotate[i] = false;
                        readOnly[i] = true;
                }
                break;
        default:
                UNREACHABLE;
        }
}
 
void SCC::generateChannels(float** bufs, unsigned num)
{
        unsigned enable = ch_enable;
        for (unsigned i = 0; i < 5; ++i, enable >>= 1) {
                if ((enable & 1) && (volume[i] || out[i])) {
                        auto out2 = out[i];
                        unsigned count2 = count[i];
                        unsigned pos2 = pos[i];
                        unsigned incr2 = incr[i];
                        unsigned period2 = period[i] + 1;
                        for (auto j : xrange(num)) {
                                bufs[i][j] += out2;
                                count2 += incr2;
                                // Note: only for very small periods
                                //       this will take more than 1 iteration
                                while (unlikely(count2 >= period2)) {
                                        count2 -= period2;
                                        pos2 = (pos2 + 1) % 32;
                                        out2 = volAdjustedWave[i][pos2];
                                }
                        }
                        out[i] = out2;
                        count[i] = count2;
                        pos[i] = pos2;
                } else {
                        bufs[i] = nullptr; // channel muted
                        // Update phase counter.
                        unsigned newCount = count[i] + num * incr[i];
                        count[i] = newCount % (period[i] + 1);
                        pos[i] = (pos[i] + newCount / (period[i] + 1)) % 32;
                        // Channel stays off until next waveform index.
                        out[i] = 0.0f;
                }
        }
}
 
 
// Debuggable
 
SCC::Debuggable::Debuggable(MSXMotherBoard& motherBoard_, const string& name_)
        : SimpleDebuggable(motherBoard_, name_ + " SCC",
                           "SCC registers in SCC+ format", 0x100)
{
}
 
byte SCC::Debuggable::read(unsigned address, EmuTime::param time)
{
        auto& scc = OUTER(SCC, debuggable);
        if (address < 0xA0) {
                // read wave form 1..5
                return scc.readWave(address >> 5, address, time);
        } else if (address < 0xC0) {
                // freq volume block
                return scc.getFreqVol(address);
        } else if (address < 0xE0) {
                // peek deformation register
                return scc.deformValue;
        } else {
                return 0xFF;
        }
}
 
void SCC::Debuggable::write(unsigned address, byte value, EmuTime::param time)
{
        auto& scc = OUTER(SCC, debuggable);
        if (address < 0xA0) {
                // read wave form 1..5
                scc.writeWave(address >> 5, address, value);
        } else if (address < 0xC0) {
                // freq volume block
                scc.setFreqVol(address, value, time);
        } else if (address < 0xE0) {
                // deformation register
                scc.setDeformReg(value, time);
        } else {
                // ignore
        }
}
 
 
static constexpr std::initializer_list<enum_string<SCC::ChipMode>> chipModeInfo = {
        { "Real",       SCC::SCC_Real       },
        { "Compatible", SCC::SCC_Compatible },
        { "Plus",       SCC::SCC_plusmode   },
};
SERIALIZE_ENUM(SCC::ChipMode, chipModeInfo);
 
template<typename Archive>
void SCC::serialize(Archive& ar, unsigned /*version*/)
{
        ar.serialize("mode",        currentChipMode,
                     "period",      orgPeriod,
                     "volume",      volume,
                     "ch_enable",   ch_enable,
                     "deformTimer", deformTimer,
                     "deform",      deformValue);
        // multi-dimensional arrays are not directly support by the
        // serialization framework, maybe in the future. So for now
        // manually loop over the channels.
        char tag[6] = { 'w', 'a', 'v', 'e', 'X', 0 };
        for (auto [channel, wv] : enumerate(wave)) {
                tag[4] = char('1' + channel);
                ar.serialize(tag, wv); // signed char
        }
 
        if (ar.isLoader()) {
                // recalculate volAdjustedWave
                for (auto channel : xrange(5)) {
                        for (auto p : xrange(32)) {
                                volAdjustedWave[channel][p] =
                                        adjust(wave[channel][p], volume[channel]);
                        }
                }
 
                // recalculate rotate[5] and readOnly[5]
                setDeformRegHelper(deformValue);
 
                // recalculate incr[5] and period[5]
                //  this also (possibly) changes count[5], pos[5] and out[5]
                //  as an unwanted side-effect, so (de)serialize those later
                // Don't use current time, but instead use deformTimer, to
                // avoid changing the value of deformTimer.
                EmuTime::param time = deformTimer.getTime();
                for (auto channel : xrange(5)) {
                        unsigned per = orgPeriod[channel];
                        setFreqVol(2 * channel + 0, (per & 0x0FF) >> 0, time);
                        setFreqVol(2 * channel + 1, (per & 0xF00) >> 8, time);
                }
        }
 
        // call to setFreqVol() modifies these variables, see above
        ar.serialize("count", count,
                     "pos",   pos,
                     "out",   out); // note: changed int->float, but no need to bump serialize-version
}
INSTANTIATE_SERIALIZE_METHODS(SCC);
 
} // namespace openmsx