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[mc6847] improvements #54

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[mc6847] improvements #54

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c626dfe
make border color change only on active area
nippur72 Mar 5, 2021
e360500
allow the fetch callback to know the fetch x position
nippur72 Mar 5, 2021
0952bc0
allow custom color palette
nippur72 Mar 5, 2021
274387d
allow MC6847 to run at variable tick speed
nippur72 Mar 5, 2021
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83 changes: 51 additions & 32 deletions chips/mc6847.h
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,7 @@ extern "C" {
#define MC6847_BOTTOM_BORDER_LINES (26) /* 26 lines bottom border */
#define MC6847_VRETRACE_LINES (6) /* 6 'lines' for vertical retrace */
#define MC6847_ALL_LINES (262) /* all of the above */
#define MC6847_TICKS_PER_SCANLINE (228) /* number of ticks per scan line */
#define MC6847_DISPLAY_START (MC6847_VBLANK_LINES+MC6847_TOP_BORDER_LINES)
#define MC6847_DISPLAY_END (MC6847_DISPLAY_START+MC6847_DISPLAY_LINES)
#define MC6847_BOTTOM_BORDER_END (MC6847_DISPLAY_END+MC6847_BOTTOM_BORDER_LINES)
Expand All @@ -186,8 +187,8 @@ extern "C" {
/* horizontal border width */
#define MC6847_BORDER_PIXELS ((MC6847_DISPLAY_WIDTH-MC6847_IMAGE_WIDTH)/2)

/* the MC6847 is always clocked at 3.579 MHz */
#define MC6847_TICK_HZ (3579545)
/* the MC6847 is normally clocked at 3.579 MHz */
#define MC6847_STANDARD_TICK_HZ (3579545)

/* fixed point precision for more precise error accumulation */
#define MC6847_FIXEDPOINT_SCALE (16)
Expand All @@ -199,11 +200,14 @@ typedef uint64_t (*mc6847_fetch_t)(uint64_t pins, void* user_data);
typedef struct {
/* the CPU tick rate in hz */
int tick_hz;
/* the MC6847 tick rate in hz */
int mc6847_tick_hz;
/* pointer to an RGBA8 framebuffer where video image is written to */
uint32_t* rgba8_buffer;
/* size of rgba8_buffer in bytes (must be at least 320*244*4=312320 bytes) */
uint32_t rgba8_buffer_size;
/* memory-fetch callback */
uint32_t *palette;
mc6847_fetch_t fetch_cb;
/* optional user-data for the fetch callback */
void* user_data;
Expand All @@ -223,12 +227,16 @@ typedef struct {
uint32_t alnum_orange;
uint32_t alnum_dark_orange;

/* border color, picked only at end of active area */
uint32_t border_color;

/* internal counters */
int h_count;
int h_sync_start;
int h_sync_end;
int h_period;
int l_count;
int h_fetchpos;

/* true during field-sync */
bool fs;
Expand Down Expand Up @@ -268,26 +276,22 @@ void mc6847_init(mc6847_t* vdg, const mc6847_desc_t* desc) {
CHIPS_ASSERT(desc->rgba8_buffer);
CHIPS_ASSERT(desc->rgba8_buffer_size >= (MC6847_DISPLAY_WIDTH*MC6847_DISPLAY_HEIGHT*sizeof(uint32_t)));
CHIPS_ASSERT(desc->fetch_cb);
CHIPS_ASSERT((desc->tick_hz > 0) && (desc->tick_hz < MC6847_TICK_HZ));
CHIPS_ASSERT(desc->tick_hz > 0);
CHIPS_ASSERT(desc->mc6847_tick_hz > 0);

memset(vdg, 0, sizeof(*vdg));
vdg->rgba8_buffer = desc->rgba8_buffer;
vdg->fetch_cb = desc->fetch_cb;
vdg->user_data = desc->user_data;

/* compute counter periods, the MC6847 is always clocked at 3.579 MHz,
and the frequency of how the tick function is called must be
communicated to the init function

one scanline is 228 3.5 MC6847 ticks
*/
int64_t tmp = (228LL * desc->tick_hz * MC6847_FIXEDPOINT_SCALE) / MC6847_TICK_HZ;
/* compute counter periods */
int64_t tmp = (((int64_t) MC6847_TICKS_PER_SCANLINE) * desc->tick_hz * MC6847_FIXEDPOINT_SCALE) / desc->mc6847_tick_hz;
vdg->h_period = (int) tmp;
/* hsync starts at tick 10 of a scanline */
tmp = (10LL * desc->tick_hz * MC6847_FIXEDPOINT_SCALE) / MC6847_TICK_HZ;
tmp = (10LL * desc->tick_hz * MC6847_FIXEDPOINT_SCALE) / desc->mc6847_tick_hz;
vdg->h_sync_start = (int) tmp;
/* hsync is 16 ticks long */
tmp = (26LL * desc->tick_hz * MC6847_FIXEDPOINT_SCALE) / MC6847_TICK_HZ;
tmp = (26LL * desc->tick_hz * MC6847_FIXEDPOINT_SCALE) / desc->mc6847_tick_hz;
vdg->h_sync_end = (int) tmp;

/* the default graphics mode color palette
Expand All @@ -312,21 +316,33 @@ void mc6847_init(mc6847_t* vdg, const mc6847_desc_t* desc) {

color intensities are slightly boosted
*/
vdg->palette[0] = _MC6847_RGBA(19, 146, 11); /* green */
vdg->palette[1] = _MC6847_RGBA(155, 150, 10); /* yellow */
vdg->palette[2] = _MC6847_RGBA(2, 22, 175); /* blue */
vdg->palette[3] = _MC6847_RGBA(155, 22, 7); /* red */
vdg->palette[4] = _MC6847_RGBA(141, 150, 154); /* buff */
vdg->palette[5] = _MC6847_RGBA(15, 143, 155); /* cyan */
vdg->palette[6] = _MC6847_RGBA(139, 39, 155); /* cyan */
vdg->palette[7] = _MC6847_RGBA(140, 31, 11); /* orange */

/* black level color, and alpha-numeric display mode colors */
vdg->black = 0xFF111111;
vdg->alnum_green = _MC6847_RGBA(19, 146, 11);
vdg->alnum_dark_green = 0xFF002400;
vdg->alnum_orange = _MC6847_RGBA(140, 31, 11);
vdg->alnum_dark_orange = 0xFF000E22;
if(desc->palette == NULL) {
vdg->palette[0] = _MC6847_RGBA(19, 146, 11); /* green */
vdg->palette[1] = _MC6847_RGBA(155, 150, 10); /* yellow */
vdg->palette[2] = _MC6847_RGBA(2, 22, 175); /* blue */
vdg->palette[3] = _MC6847_RGBA(155, 22, 7); /* red */
vdg->palette[4] = _MC6847_RGBA(141, 150, 154); /* buff */
vdg->palette[5] = _MC6847_RGBA(15, 143, 155); /* cyan */
vdg->palette[6] = _MC6847_RGBA(139, 39, 155); /* cyan */
vdg->palette[7] = _MC6847_RGBA(140, 31, 11); /* orange */

/* black level color, and alpha-numeric display mode colors */
vdg->black = 0xFF111111;
vdg->alnum_green = _MC6847_RGBA(19, 146, 11);
vdg->alnum_dark_green = 0xFF002400;
vdg->alnum_orange = _MC6847_RGBA(140, 31, 11);
vdg->alnum_dark_orange = 0xFF000E22;
} else {
/* custom palette */
for(int i=0; i<8; i++) {
vdg->palette[i] = desc->palette[i];
}
vdg->black = desc->palette[8];
vdg->alnum_green = desc->palette[9];
vdg->alnum_dark_green = desc->palette[10];
vdg->alnum_orange = desc->palette[11];
vdg->alnum_dark_orange = desc->palette[12];
}
}

void mc6847_reset(mc6847_t* vdg) {
Expand Down Expand Up @@ -420,20 +436,20 @@ static inline uint32_t _mc6847_border_color(mc6847_t* vdg, uint64_t pins) {

static void _mc6847_decode_border(mc6847_t* vdg, uint64_t pins, int y) {
uint32_t* dst = &(vdg->rgba8_buffer[y * MC6847_DISPLAY_WIDTH]);
uint32_t c = _mc6847_border_color(vdg, pins);
for (int x = 0; x < MC6847_DISPLAY_WIDTH; x++) {
*dst++ = c;
*dst++ = vdg->border_color;
}
}

static uint64_t _mc6847_decode_scanline(mc6847_t* vdg, uint64_t pins, int y) {
uint32_t* dst = &(vdg->rgba8_buffer[(y+MC6847_TOP_BORDER_LINES) * MC6847_DISPLAY_WIDTH]);
uint32_t bc = _mc6847_border_color(vdg, pins);
vdg->border_color = _mc6847_border_color(vdg, pins);

void* ud = vdg->user_data;

/* left border */
for (int i = 0; i < MC6847_BORDER_PIXELS; i++) {
*dst++ = bc;
*dst++ = vdg->border_color;
}

/* visible scanline */
Expand All @@ -455,6 +471,7 @@ static uint64_t _mc6847_decode_scanline(mc6847_t* vdg, uint64_t pins, int y) {
uint32_t fg_color = (pins & MC6847_CSS) ? vdg->palette[4] : vdg->palette[0];
for (int x = 0; x < bytes_per_row; x++) {
MC6847_SET_ADDR(pins, addr++);
vdg->h_fetchpos = x;
pins = vdg->fetch_cb(pins, ud);
uint8_t m = MC6847_GET_DATA(pins);
for (int p = 7; p >= 0; p--) {
Expand All @@ -481,6 +498,7 @@ static uint64_t _mc6847_decode_scanline(mc6847_t* vdg, uint64_t pins, int y) {
uint16_t addr = (y / row_height) * bytes_per_row;
for (int x = 0; x < bytes_per_row; x++) {
MC6847_SET_ADDR(pins, addr++);
vdg->h_fetchpos = x;
pins = vdg->fetch_cb(pins, ud);
uint8_t m = MC6847_GET_DATA(pins);
for (int p = 6; p >= 0; p -= 2) {
Expand All @@ -506,6 +524,7 @@ static uint64_t _mc6847_decode_scanline(mc6847_t* vdg, uint64_t pins, int y) {
uint32_t alnum_bg = (pins & MC6847_CSS) ? vdg->alnum_dark_orange : vdg->alnum_dark_green;
for (int x = 0; x < 32; x++) {
MC6847_SET_ADDR(pins, addr++);
vdg->h_fetchpos = x;
pins = vdg->fetch_cb(pins, ud);
uint8_t chr = MC6847_GET_DATA(pins);
if (pins & MC6847_AS) {
Expand Down Expand Up @@ -568,7 +587,7 @@ static uint64_t _mc6847_decode_scanline(mc6847_t* vdg, uint64_t pins, int y) {

/* right border */
for (int i = 0; i < MC6847_BORDER_PIXELS; i++) {
*dst++ = bc;
*dst++ = vdg->border_color;
}

return pins;
Expand Down