CasImage.cc

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#include "CasImage.hh"
#include "File.hh"
#include "Filename.hh"
#include "CliComm.hh"
#include "Clock.hh"
#include "MSXException.hh"
#include "xrange.hh"
#include <cstring> // for memcmp

namespace openmsx {

// output settings

// a higher baudrate doesn't work anymore, but it is unclear why, because 4600
// baud should work (known from Speedsave 4000 and Turbo 5000 programs).
// 3765 still works on a Toshiba HX-10 and Philips NMS 8250, but not on a
// Panasonic FS-A1WSX, on which 3763 is the max. National CF-2000 has 3762 as
// the max. Let's take 3760 then as a safe value.
// UPDATE: that seems to break RUN"CAS:" type of programs. 3744 seems to work
// for those as well (we don't understand why yet)
static const unsigned BAUDRATE = 3744;
static const unsigned OUTPUT_FREQUENCY = 4 * BAUDRATE; // 4 samples per bit
// We oversample the audio signal for better sound quality (especially in
// combination with the hq resampler). Without oversampling the audio output
// could contain portions like this:
//   -1, +1, -1, +1, -1, +1, ...
// So it contains a signal at the Nyquist frequency. The hq resampler contains
// a low-pass filter, and (all practically implementable) filters cut off a
// portion of the spectrum near the Nyquist freq. So this high freq signal was
// lost after the hq resampler. After oversampling, the signal looks like this:
//   -1, -1, -1, -1, +1, +1, +1, +1, -1, -1, -1, -1, ...
// So every sample repeated 4 times.
static const unsigned AUDIO_OVERSAMPLE = 4;

// number of output bytes for silent parts
static const unsigned SHORT_SILENCE = OUTPUT_FREQUENCY * 1; // 1 second
static const unsigned LONG_SILENCE  = OUTPUT_FREQUENCY * 2; // 2 seconds

// number of 1-bits for headers
static const unsigned LONG_HEADER  = 16000 / 2;
static const unsigned SHORT_HEADER =  4000 / 2;

// headers definitions
static const byte CAS_HEADER   [ 8] = { 0x1F,0xA6,0xDE,0xBA,0xCC,0x13,0x7D,0x74 };
static const byte ASCII_HEADER [10] = { 0xEA,0xEA,0xEA,0xEA,0xEA,0xEA,0xEA,0xEA,0xEA,0xEA };
static const byte BINARY_HEADER[10] = { 0xD0,0xD0,0xD0,0xD0,0xD0,0xD0,0xD0,0xD0,0xD0,0xD0 };
static const byte BASIC_HEADER [10] = { 0xD3,0xD3,0xD3,0xD3,0xD3,0xD3,0xD3,0xD3,0xD3,0xD3 };


CasImage::CasImage(const Filename& filename, FilePool& filePool, CliComm& cliComm)
{
        setFirstFileType(CassetteImage::UNKNOWN);
        convert(filename, filePool, cliComm);
}

short CasImage::getSampleAt(EmuTime::param time)
{
        static const Clock<OUTPUT_FREQUENCY> zero(EmuTime::zero);
        unsigned pos = zero.getTicksTill(time);
        return pos < output.size() ? output[pos] * 256 : 0;
}

EmuTime CasImage::getEndTime() const
{
        Clock<OUTPUT_FREQUENCY> clk(EmuTime::zero);
        clk += unsigned(output.size());
        return clk.getTime();
}

unsigned CasImage::getFrequency() const
{
        return OUTPUT_FREQUENCY * AUDIO_OVERSAMPLE;
}

void CasImage::fillBuffer(unsigned pos, int** bufs, unsigned num) const
{
        size_t nbSamples = output.size();
        if ((pos / AUDIO_OVERSAMPLE) < nbSamples) {
                for (auto i : xrange(num)) {
                        bufs[0][i] = ((pos / AUDIO_OVERSAMPLE) < nbSamples)
                                   ? output[pos / AUDIO_OVERSAMPLE] * 256
                                   : 0;
                        ++pos;
                }
        } else {
                bufs[0] = nullptr;
        }
}

void CasImage::write0()
{
        output.push_back( 127);
        output.push_back( 127);
        output.push_back(-127);
        output.push_back(-127);
}
void CasImage::write1()
{
        output.push_back( 127);
        output.push_back(-127);
        output.push_back( 127);
        output.push_back(-127);
}

// write a header signal
void CasImage::writeHeader(int s)
{
        for (int i = 0; i < s; ++i) {
                write1();
        }
}

// write silence
void CasImage::writeSilence(int s)
{
        output.insert(output.end(), s, 0);
}

// write a byte
void CasImage::writeByte(byte b)
{
        // one start bit
        write0();
        // eight data bits
        for (auto i : xrange(8)) {
                if (b & (1 << i)) {
                        write1();
                } else {
                        write0();
                }
        }
        // two stop bits
        write1();
        write1();
}

// write data until a header is detected
bool CasImage::writeData(const byte* buf, size_t size, size_t& pos)
{
        bool eof = false;
        while ((pos + 8) <= size) {
                if (!memcmp(&buf[pos], CAS_HEADER, 8)) {
                        return eof;
                }
                writeByte(buf[pos]);
                if (buf[pos] == 0x1A) {
                        eof = true;
                }
                pos++;
        }
        while (pos < size) {
                writeByte(buf[pos++]);
        }
        return false;
}

void CasImage::convert(const Filename& filename, FilePool& filePool, CliComm& cliComm)
{
        File file(filename);
        size_t size;
        const byte* buf = file.mmap(size);

        // search for a header in the .cas file
        bool issueWarning = false;
        bool headerFound = false;
        bool firstFile = true;
        size_t pos = 0;
        while ((pos + 8) <= size) {
                if (!memcmp(&buf[pos], CAS_HEADER, 8)) {
                        // it probably works fine if a long header is used for every
                        // header but since the msx bios makes a distinction between
                        // them, we do also (hence a lot of code).
                        headerFound = true;
                        pos += 8;
                        writeSilence(LONG_SILENCE);
                        writeHeader(LONG_HEADER);
                        if ((pos + 10) <= size) {
                                // determine file type
                                FileType type = CassetteImage::UNKNOWN;
                                if (!memcmp(&buf[pos], ASCII_HEADER, 10)) {
                                        type = CassetteImage::ASCII;
                                } else if (!memcmp(&buf[pos], BINARY_HEADER, 10)) {
                                        type = CassetteImage::BINARY;
                                } else if (!memcmp(&buf[pos], BASIC_HEADER, 10)) {
                                        type = CassetteImage::BASIC;
                                }
                                if (firstFile) setFirstFileType(type);
                                switch (type) {
                                        case CassetteImage::ASCII:
                                                writeData(buf, size, pos);
                                                bool eof;
                                                do {
                                                        pos += 8;
                                                        writeSilence(SHORT_SILENCE);
                                                        writeHeader(SHORT_HEADER);
                                                        eof = writeData(buf, size, pos);
                                                } while (!eof && ((pos + 8) <= size));
                                                break;
                                        case CassetteImage::BINARY:
                                        case CassetteImage::BASIC:
                                                writeData(buf, size, pos);
                                                writeSilence(SHORT_SILENCE);
                                                writeHeader(SHORT_HEADER);
                                                pos += 8;
                                                writeData(buf, size, pos);
                                                break;
                                        default:
                                                // unknown file type: using long header
                                                writeData(buf, size, pos);
                                                break;
                                }
                        } else {
                                // unknown file type: using long header
                                writeData(buf, size, pos);
                        }
                        firstFile = false;
                } else {
                        // should not occur
                        PRT_DEBUG("CAS2WAV: skipping unhandled data");
                        pos++;
                        issueWarning = true;
                }
        }
        if (!headerFound) {
                throw MSXException(filename.getOriginal() +
                                   ": not a valid CAS image");
        }
        if (issueWarning) {
                 cliComm.printWarning("Skipped unhandled data in " +
                                      filename.getOriginal());
        }

        // conversion successful, now calc sha1sum
        file.setFilePool(filePool);
        setSha1Sum(file.getSha1Sum());
}

} // namespace openmsx