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// license:BSD-3-Clause
// copyright-holders:Sean Young
#include <assert.h>
#include "svi_cas.h"
#define CAS_PERIOD_0 (37)
#define CAS_PERIOD_1 (18)
#define CAS_HEADER_PERIODS (1600)
#define CAS_EMPTY_SAMPLES (24220)
#define CAS_INIT_SAMPLES (200)
static const uint8_t CasHeader[17] =
{
0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55,
0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x7f
};
#define SMPLO -32768
#define SMPHI 32767
static int cas_size;
/*******************************************************************
Generate samples for the tape image
********************************************************************/
static int svi_cas_fill_wave(int16_t *buffer, int sample_count, uint8_t *bytes)
{
int cas_pos, samples_pos, n, i;
cas_pos = 17;
samples_pos = 0;
/* write CAS_INIT_SAMPLES of silence */
n = CAS_INIT_SAMPLES; while (n--) buffer[samples_pos++] = 0;
while (samples_pos < sample_count && cas_pos < cas_size)
{
/* write CAS_HEADER_PERIODS of header */
for (i=0;i<CAS_HEADER_PERIODS;i++)
{
/* write a "0" */
n = !(i % 4) ? 21 : 18;
while (n--) buffer[samples_pos++] = SMPHI;
n = 19; while (n--) buffer[samples_pos++] = SMPLO;
/* write a "1" */
n = 9; while (n--) buffer[samples_pos++] = SMPHI;
n = 9; while (n--) buffer[samples_pos++] = SMPLO;
}
/* write "0x7f" */
/* write a "0" */
n = 21; while (n--) buffer[samples_pos++] = SMPHI;
n = 19; while (n--) buffer[samples_pos++] = SMPLO;
for (i=0;i<7;i++)
{
/* write a "1" */
n = 9; while (n--) buffer[samples_pos++] = SMPHI;
n = 9; while (n--) buffer[samples_pos++] = SMPLO;
}
while (samples_pos < sample_count && cas_pos < cas_size)
{
n = 21; while (n--) buffer[samples_pos++] = SMPHI;
n = 19; while (n--) buffer[samples_pos++] = SMPLO;
for (i=0;i<8;i++)
{
int bit = (bytes[cas_pos] & (0x80 >> i) );
/* write this one bit */
if (bit)
{
/* write a "1" */
n = 9; while (n--) buffer[samples_pos++] = SMPHI;
n = 9; while (n--) buffer[samples_pos++] = SMPLO;
}
else
{
/* write a "0" */
n = 18; while (n--) buffer[samples_pos++] = SMPHI;
n = 19; while (n--) buffer[samples_pos++] = SMPLO;
}
}
cas_pos++;
/* check if we've hit a new header (or end of block) */
if ( (cas_pos + 17) < cas_size)
{
if (!memcmp (bytes + cas_pos, CasHeader, 17) )
{
cas_pos += 17;
/* end of block marker */
n = CAS_EMPTY_SAMPLES; while (n--) buffer[samples_pos++] = SMPHI;
break; /* falls back to loop above; plays header again */
}
}
}
}
/* end of block marker */
n = CAS_EMPTY_SAMPLES; while (n--) buffer[samples_pos++] = SMPHI;
return samples_pos;
}
/*******************************************************************
Calculate the number of samples needed for this tape image
********************************************************************/
static int svi_cas_to_wav_size(const uint8_t *casdata, int caslen)
{
int cas_pos, samples_pos, size, i;
if (caslen < 17) return -1;
if (memcmp (casdata, CasHeader, sizeof (CasHeader) ) ) return -1;
cas_size = caslen;
cas_pos = 17;
samples_pos = CAS_INIT_SAMPLES;
while (cas_pos < caslen)
{
size = CAS_HEADER_PERIODS * ( CAS_PERIOD_0 + CAS_PERIOD_1 ) +
( CAS_HEADER_PERIODS / 4 ) * 3;
samples_pos += size;
samples_pos += 21 + 19 + 7 * CAS_PERIOD_1;
while (cas_pos < caslen)
{
samples_pos += 21;
samples_pos += 19;
for (i=0;i<8;i++)
{
int bit = (casdata[cas_pos] & (0x80 >> i) );
samples_pos += bit ? CAS_PERIOD_1 : CAS_PERIOD_0;
}
cas_pos++;
/* check if we've hit a new header (or end of block) */
if ( (cas_pos + 17) < caslen)
{
if (!memcmp (casdata + cas_pos, CasHeader, 17) )
{
cas_pos += 17;
/* end of block marker */
samples_pos += CAS_EMPTY_SAMPLES;
break; /* falls back to loop above; plays header again */
}
}
}
}
/* end of block marker */
samples_pos += CAS_EMPTY_SAMPLES;
return samples_pos;
}
static const struct CassetteLegacyWaveFiller svi_legacy_fill_wave =
{
svi_cas_fill_wave, /* fill_wave */
-1, /* chunk_size */
0, /* chunk_samples */
svi_cas_to_wav_size, /* chunk_sample_calc */
44100, /* sample_frequency */
0, /* header_samples */
0 /* trailer_samples */
};
static cassette_image::error svi_cas_identify(cassette_image *cassette, struct CassetteOptions *opts)
{
return cassette_legacy_identify(cassette, opts, &svi_legacy_fill_wave);
}
static cassette_image::error svi_cas_load(cassette_image *cassette)
{
return cassette_legacy_construct(cassette, &svi_legacy_fill_wave);
}
static const struct CassetteFormat svi_cas_format =
{
"cas",
svi_cas_identify,
svi_cas_load,
nullptr
};
CASSETTE_FORMATLIST_START(svi_cassette_formats)
CASSETTE_FORMAT(svi_cas_format)
CASSETTE_FORMATLIST_END
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