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mos6561 sound & misc improvements #39

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mos6561 sound & misc improvements #39

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018599c
mos6561 sound improvements
nippur72 Jul 16, 2020
8876c66
fix Y-offset register to count two lines
nippur72 Jul 20, 2020
eafcba6
adapt screen geometry to double Y-offset register
nippur72 Jul 20, 2020
9be494d
fix left offscreen display
nippur72 Jul 22, 2020
d1e80f2
fix right offscreen display
nippur72 Jul 22, 2020
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155 changes: 85 additions & 70 deletions chips/m6561.h
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Original file line number Diff line number Diff line change
Expand Up @@ -185,23 +185,27 @@ typedef struct {

/* sound generator state */
typedef struct {
uint16_t count; /* count down with clock frequency */
uint16_t period; /* counter reload value */
uint8_t bit; /* toggled between 0 and 1 */
uint16_t count; /* count up with channel frequency */
uint16_t freq; /* counter reload value */
uint8_t sreg; /* 8 bit shift register */
uint8_t enabled; /* 1 if enabled */
float output; /* output of the generator */
} m6561_voice_t;

typedef struct {
uint16_t count;
uint16_t period;
uint32_t shift;
uint8_t bit;
uint8_t enabled;
uint16_t count; /* count up with channel frequency */
uint16_t freq; /* counter reload value */
uint8_t sreg; /* 8 bit shift register */
uint16_t LFSR; /* 16 bit LFSR */
uint8_t LFSR0_old; /* bit LFSR(0) at previous step, for edge detection */
uint8_t enabled; /* 1 if enabled */
float output; /* output of the generator */
} m6561_noise_t;

typedef struct {
m6561_voice_t voice[3];
m6561_noise_t noise;
uint8_t divider_counter;
uint8_t volume;
int sample_period;
int sample_counter;
Expand Down Expand Up @@ -314,7 +318,6 @@ void m6561_init(m6561_t* vic, const m6561_desc_t* desc) {
vic->sound.sample_period = (desc->tick_hz * _M6561_FIXEDPOINT_SCALE) / desc->sound_hz;
vic->sound.sample_counter = vic->sound.sample_period;
vic->sound.sample_mag = desc->sound_magnitude;
vic->sound.noise.shift = 0x7FFFFC;
}

static void _m6561_reset_crt(m6561_t* vic) {
Expand Down Expand Up @@ -344,7 +347,10 @@ static void _m6561_reset_audio(m6561_t* vic) {
}
memset(&vic->sound.noise, 0, sizeof(m6561_noise_t));
vic->sound.volume = 0;
vic->sound.noise.shift = 0x7FFFF8;
vic->sound.divider_counter = 0;
vic->sound.noise.sreg = 0;
vic->sound.noise.LFSR = 0;
vic->sound.noise.LFSR0_old = 0;
}

void m6561_reset(m6561_t* vic) {
Expand Down Expand Up @@ -379,7 +385,7 @@ static void _m6561_regs_dirty(m6561_t* vic) {
vic->rs.row_height = (vic->regs[3] & 1) ? 16 : 8;
vic->border.left = vic->regs[0] & 0x7F;
vic->border.right = vic->border.left + (vic->regs[2] & 0x7F) * 2;
vic->border.top = vic->regs[1];
vic->border.top = vic->regs[1] * 2;
vic->border.bottom = vic->border.top + ((vic->regs[3]>>1) & 0x3F) * vic->rs.row_height;
vic->gunit.inv_color = (vic->regs[15] & 8) == 0;
vic->gunit.bg_color = _m6561_colors[(vic->regs[15]>>4) & 0xF];
Expand All @@ -388,15 +394,10 @@ static void _m6561_regs_dirty(m6561_t* vic) {
vic->mem.g_addr_base = ((vic->regs[5] & 0xF)<<10); // A13..A10
vic->mem.c_addr_base = (((vic->regs[5]>>4)&0xF)<<10) | // A13..A10
(((vic->regs[2]>>7)&1)<<9); // A9
vic->sound.voice[0].enabled = 0 != (vic->regs[10] & 0x80);
vic->sound.voice[0].period = 0x80 * (0x80 - (vic->regs[10] & 0x7F));
vic->sound.voice[1].enabled = 0 != (vic->regs[11] & 0x80);
vic->sound.voice[1].period = 0x40 * (0x80 - (vic->regs[11] & 0x7F));
vic->sound.voice[2].enabled = 0 != (vic->regs[12] & 0x80);
vic->sound.voice[2].period = 0x20 * (0x80 - (vic->regs[12] & 0x7F));
vic->sound.noise.enabled = 0 != (vic->regs[13] & 0x80);
/* 0x40 factor is not a bug, tweaked to 'sound right' */
vic->sound.noise.period = 0x40 * (0x80 - (vic->regs[13] & 0x7F));
vic->sound.voice[0].enabled = 0 != (vic->regs[10] & 0x80); vic->sound.voice[0].freq = vic->regs[10] & 0x7F;
vic->sound.voice[1].enabled = 0 != (vic->regs[11] & 0x80); vic->sound.voice[1].freq = vic->regs[11] & 0x7F;
vic->sound.voice[2].enabled = 0 != (vic->regs[12] & 0x80); vic->sound.voice[2].freq = vic->regs[12] & 0x7F;
vic->sound.noise.enabled = 0 != (vic->regs[13] & 0x80); vic->sound.noise.freq = vic->regs[13] & 0x7F;
vic->sound.volume = vic->regs[14] & 0xF;
}

Expand Down Expand Up @@ -440,7 +441,6 @@ static inline void _m6561_decode_pixels(m6561_t* vic, uint32_t* dst) {
dst[2] = (p & (1<<5)) ? fg : bg;
dst[3] = (p & (1<<4)) ? fg : bg;
}
vic->gunit.shift = p<<4;
}
}

Expand All @@ -466,6 +466,7 @@ static void _m6561_tick_video(m6561_t* vic) {
uint32_t* dst = vic->crt.rgba8_buffer + (y * w + x) * _M6561_PIXELS_PER_TICK;
_m6561_decode_pixels(vic, dst);
}
vic->gunit.shift = vic->gunit.shift<<4;
}

/* display-enabled area? */
Expand All @@ -478,7 +479,7 @@ static void _m6561_tick_video(m6561_t* vic) {
/* switch off horizontal border */
vic->border.enabled &= ~_M6561_HBORDER;
}
if (vic->rs.h_count == (vic->border.right+1)) {
if (vic->rs.h_count == (vic->border.right+1) || vic->rs.h_count == _M6561_HTOTAL - 1) {
/* switch on horizontal border */
vic->border.enabled |= _M6561_HBORDER;
vic->rs.vc_disabled |= _M6561_HVC_DISABLE;
Expand Down Expand Up @@ -513,7 +514,7 @@ static void _m6561_tick_video(m6561_t* vic) {
if (vic->rs.rc == vic->rs.row_height) {
vic->rs.rc = 0;
vic->rs.row_count++;
vic->rs.vc_base = vic->rs.vc & 0xFFFE;
vic->rs.vc_base = vic->rs.row_count*((vic->regs[2] & 0x7F) * 2);
}
if (vic->rs.v_count == vic->border.top) {
vic->border.enabled &= ~_M6561_VBORDER;
Expand Down Expand Up @@ -541,18 +542,6 @@ static void _m6561_tick_video(m6561_t* vic) {
}

/*--- audio engine code ---*/
#define _M6561_BIT(val,bitnr) ((val>>bitnr)&1)
static inline float _m6561_noise_ampl(uint32_t noise_shift) {
uint32_t amp = (_M6561_BIT(noise_shift,22)<<7) |
(_M6561_BIT(noise_shift,20)<<6) |
(_M6561_BIT(noise_shift,16)<<5) |
(_M6561_BIT(noise_shift,13)<<4) |
(_M6561_BIT(noise_shift,11)<<3) |
(_M6561_BIT(noise_shift,7)<<2) |
(_M6561_BIT(noise_shift,4)<<1) |
(_M6561_BIT(noise_shift,2)<<0);
return ((float)amp) / 256.0f;
}

/* center positive volume value around zero */
static inline float _m6561_dcadjust(m6561_sound_t* snd, float s) {
Expand All @@ -563,43 +552,69 @@ static inline float _m6561_dcadjust(m6561_sound_t* snd, float s) {
return s - (snd->dcadj_sum / M6561_DCADJ_BUFLEN);
}

/* tick the audio engine, return true if a new sample if ready */
static uint64_t _m6561_tick_audio(m6561_t* vic, uint64_t pins) {
m6561_sound_t* snd = &vic->sound;
/* tick tone voices */
for (int i = 0; i < 3; i++) {
m6561_voice_t* voice = &snd->voice[i];
if (voice->count == 0) {
voice->count = voice->period;
voice->bit = !voice->bit;
}
else {
voice->count--;
}
if (voice->bit && voice->enabled) {
snd->sample_accum += 1.0f;
}
static void _m6561_tick_voice(m6561_voice_t* voice) {
voice->count = (voice->count + 1) & 0x7f;

if (voice->count == 127) {
voice->count = voice->freq;
voice->sreg = (voice->sreg << 1) | (~((voice->sreg & 128) >> 7) & voice->enabled);
}
/* tick noice channel */
{
m6561_noise_t* noise = &snd->noise;
if (noise->count == 0) {
noise->count = noise->period;
noise->bit = !noise->bit;
if (noise->bit) {
uint32_t s = noise->shift;
/* FIXME(?): m6581 uses (s>>17), MAME is (s>>13) */
uint32_t new_bit = ((s>>22)^(s>>13)) & 1;
noise->shift = ((s<<1)|new_bit) & 0x007FFFFF;
}
}
else {
noise->count--;
}
if (noise->bit && noise->enabled) {
snd->sample_accum += _m6561_noise_ampl(noise->shift);
}

if (voice->enabled) {
if(voice->sreg & 1) voice->output = 1.0f;
else voice->output = 0.0f;
}
else {
voice->output = 0.5f;
}
}

static void _m6561_tick_noise(m6561_noise_t* noise) {
noise->count = (noise->count + 1) & 0x7f;

if (noise->count == 127) {
noise->count = noise->freq;

uint8_t LFSR0 = noise->LFSR & 1;

// shifts the 8 bit SR at edge detection of LFSR[0]
if (noise->LFSR0_old == 0 && LFSR0 == 1) {
noise->sreg = (noise->sreg << 1) | (~((noise->sreg & 128) >> 7) & noise->enabled);
}

// shifts the 16 bit LFSR
noise->LFSR0_old = LFSR0; // save bit for edge detection
uint8_t gate1 = ((noise->LFSR >> 3) ^ (noise->LFSR >> 12)) & 1;
uint8_t gate2 = ((noise->LFSR >> 14) ^ (noise->LFSR >> 15)) & 1;
uint8_t gate3 = ~(gate1 ^ gate2);
LFSR0 = (gate3 & noise->enabled);
noise->LFSR = (noise->LFSR << 1) | LFSR0;
}

if (noise->enabled) {
if (noise->sreg & 1) noise->output = 1.0f;
else noise->output = 0.0f;
}
else {
noise->output = 0.5f;
}
}

/* tick the audio engine, return true if a new sample is ready */
static uint64_t _m6561_tick_audio(m6561_t* vic, uint64_t pins) {
m6561_sound_t* snd = &vic->sound;

snd->divider_counter++;
if ((snd->divider_counter & 15) == 0) _m6561_tick_voice(&snd->voice[0]);
if ((snd->divider_counter & 7) == 0) _m6561_tick_voice(&snd->voice[1]);
if ((snd->divider_counter & 3) == 0) _m6561_tick_voice(&snd->voice[2]);
if ((snd->divider_counter & 1) == 0) _m6561_tick_noise(&snd->noise);

snd->sample_accum += snd->voice[0].output +
snd->voice[1].output +
snd->voice[2].output +
snd->noise.output;

snd->sample_accum_count += 1.0f;

/* output a new sample */
Expand Down
10 changes: 6 additions & 4 deletions systems/vic20.h
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Original file line number Diff line number Diff line change
Expand Up @@ -236,13 +236,15 @@ bool vic20_is_tape_motor_on(vic20_t* sys);
#define CHIPS_ASSERT(c) assert(c)
#endif

#define _VIC20_STD_DISPLAY_WIDTH (232) /* actually 229, but rounded up to 8x */
#define _VIC20_STD_DISPLAY_HEIGHT (272)
/* checked on CRT PAL display */
#define _VIC20_DISPLAY_X (5*8)
#define _VIC20_DISPLAY_Y (6*8)
#define _VIC20_STD_DISPLAY_WIDTH (208)
#define _VIC20_STD_DISPLAY_HEIGHT (264)

#define _VIC20_DBG_DISPLAY_WIDTH ((_M6561_HTOTAL+1)*4)
#define _VIC20_DBG_DISPLAY_HEIGHT (_M6561_VTOTAL+1)
#define _VIC20_DISPLAY_SIZE (_VIC20_DBG_DISPLAY_WIDTH*_VIC20_DBG_DISPLAY_HEIGHT*4)
#define _VIC20_DISPLAY_X (32)
#define _VIC20_DISPLAY_Y (8)

static uint16_t _vic20_vic_fetch(uint16_t addr, void* user_data);
static void _vic20_init_key_map(vic20_t* sys);
Expand Down