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// license:BSD-3-Clause
// copyright-holders:Robbbert
/********************************************************************
Support for Heathkit H8 H8T cassette images
Standard Kansas City format (300 baud)
TODO - investigate 1200 buad support, H8 should support it, but H88 does not.
We output a leader, followed by the contents of the H8T file.
********************************************************************/
#include "h8_cas.h"
#include <algorithm>
static constexpr uint16_t WAVEENTRY_LOW = -32768;
static constexpr uint16_t WAVEENTRY_HIGH = 32767;
static constexpr uint16_t SILENCE = 0;
// using a multiple of 4800 will ensure an integer multiple of samples for each wave.
static constexpr uint16_t H8_WAV_FREQUENCY = 9600;
static constexpr uint16_t TAPE_BAUD_RATE = 300;
static constexpr uint16_t SAMPLES_PER_BIT = H8_WAV_FREQUENCY / TAPE_BAUD_RATE;
static constexpr uint16_t SAMPLES_PER_HALF_WAVE = SAMPLES_PER_BIT / 2;
static constexpr uint16_t ONE_FREQ = 1200;
static constexpr uint16_t ZERO_FREQ = 2400;
static constexpr uint16_t ONE_CYCLES = H8_WAV_FREQUENCY / ONE_FREQ;
static constexpr uint16_t ZERO_CYCLES = H8_WAV_FREQUENCY / ZERO_FREQ;
// image size
static int h8_image_size; // FIXME: global variable prevents multiple instances
static int h8_put_samples(int16_t *buffer, int sample_pos, int count, int level)
{
if (buffer)
{
std::fill_n(&buffer[sample_pos], count, level);
}
return count;
}
static int h8_output_bit(int16_t *buffer, int sample_pos, bool bit)
{
int samples = 0;
const int loops = bit ? ONE_CYCLES : ZERO_CYCLES;
const int samplePerValue = SAMPLES_PER_HALF_WAVE / loops;
for (int i = 0; i < loops; i++)
{
samples += h8_put_samples(buffer, sample_pos + samples, samplePerValue, WAVEENTRY_LOW);
samples += h8_put_samples(buffer, sample_pos + samples, samplePerValue, WAVEENTRY_HIGH);
}
return samples;
}
static int h8_output_byte(int16_t *buffer, int sample_pos, uint8_t data)
{
int samples = 0;
// start bit
samples += h8_output_bit(buffer, sample_pos + samples, 0);
// data bits
for (int i = 0; i < 8; i++)
{
samples += h8_output_bit(buffer, sample_pos + samples, data & 1);
data >>= 1;
}
// stop bit
samples += h8_output_bit(buffer, sample_pos + samples, 1);
return samples;
}
static int h8_handle_cassette(int16_t *buffer, const uint8_t *bytes)
{
int sample_count = 0;
// leader - 1 second
for (int i = 0; i < TAPE_BAUD_RATE; i++)
sample_count += h8_output_bit(buffer, sample_count, 1);
// data
for (int i = 0; i < h8_image_size; i++)
sample_count += h8_output_byte(buffer, sample_count, bytes[i]);
return sample_count;
}
/*******************************************************************
Generate samples for the tape image
********************************************************************/
static int h8_cassette_fill_wave(int16_t *buffer, int length, uint8_t *bytes)
{
return h8_handle_cassette(buffer, bytes);
}
/*******************************************************************
Calculate the number of samples needed for this tape image
********************************************************************/
static int h8_cassette_calculate_size_in_samples(const uint8_t *bytes, int length)
{
h8_image_size = length;
return h8_handle_cassette(nullptr, bytes);
}
static const cassette_image::LegacyWaveFiller h8_legacy_fill_wave =
{
h8_cassette_fill_wave, // fill_wave
-1, // chunk_size
0, // chunk_samples
h8_cassette_calculate_size_in_samples, // chunk_sample_calc
H8_WAV_FREQUENCY, // sample_frequency
0, // header_samples
0 // trailer_samples
};
static cassette_image::error h8_cassette_identify(cassette_image *cassette, cassette_image::Options *opts)
{
return cassette->legacy_identify(opts, &h8_legacy_fill_wave);
}
static cassette_image::error h8_cassette_load(cassette_image *cassette)
{
return cassette->legacy_construct(&h8_legacy_fill_wave);
}
static const cassette_image::Format h8_cassette_image_format =
{
"h8t",
h8_cassette_identify,
h8_cassette_load,
nullptr
};
CASSETTE_FORMATLIST_START(h8_cassette_formats)
CASSETTE_FORMAT(h8_cassette_image_format)
CASSETTE_FORMATLIST_END
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