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eia608: some changes to the API, and fix a few bugs
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@rasky
rasky committed Dec 8, 2024
1 parent 1efffca commit 504f7ab
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Showing 2 changed files with 58 additions and 44 deletions.
28 changes: 15 additions & 13 deletions include/eia608.h
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Original file line number Diff line number Diff line change
Expand Up @@ -57,14 +57,12 @@ typedef enum {

/** @brief Caption display parameters */
typedef struct {
eia608_channel_t cc; ///< Caption channel to transmit on (default: EIA608_CC1)
int row; ///< The row to display the caption on, range 1-15 (default: 11)
bool underline; ///< Enable underline for the caption (default: false)
bool hidden; ///< Prepare the caption but don't display it (default: false)
} eia608_captionparms_t;

/** @brief Calculate EIA608 parity for 7-bit value */
#define EIA608_PARITY(b) (((1 ^ ((b)>>0) ^ ((b)>>1) ^ ((b)>>2) ^ ((b)>>3) ^ ((b)>>4) ^ ((b)>>5) ^ ((b)>>6)) & 1) << 7)
#define EIA608_PARITY(b) ((((1 ^ ((b)>>0) ^ ((b)>>1) ^ ((b)>>2) ^ ((b)>>3) ^ ((b)>>4) ^ ((b)>>5) ^ ((b)>>6)) & 1) << 7) | (b))

///@cond
#define EIA608_CTRL(c) ((EIA608_PARITY((c) & 0xFF)) | (EIA608_PARITY((c) >> 8) << 8))
Expand Down Expand Up @@ -198,9 +196,16 @@ void eia608_write_ctrl_raw(eia608_ctrl_t ctrl);
* @brief Emit a caption, with automatic positioning on the screen.
*
* EIA-608 captions are divided into maximum 4 lines of 32 characters each.
* This function will automatically word-wrap the caption into the lines if
* This function will automatically word-wrap the caption into multiple lines if
* necessary, but also respects any embedded newlines in the caption.
*
* The caption will not be displayed but just prepared. You need
* to call #eia608_caption_show to actually display it. This allows for perfect
* syncing as preparing a caption can take a non trivial amount of time
* (about 1 second every 60 characters), so to avoid avoid the captions always
* a bit late, you can prepare the next sentence in advance and then show it
* when needed.
*
* By default, the caption will be displayed centered, at the bottom of the
* screen, using white on black colors. You can change these parameters by
* setting fields in the \p parms structure.
Expand All @@ -218,28 +223,25 @@ void eia608_write_ctrl_raw(eia608_ctrl_t ctrl);
* this function to display a caption before the previous one has been
* displayed, the new caption will replace the old one.
*
* @param cc Channel in which the caption must be prepared.
* @param utf8_str The UTF-8 string to display
* @param duration_secs The duration in seconds to display the caption
* @param parms Optiona parameters to control the caption
* (use NULL for default values)
*
* @see Wikipedia article on EIA-608: https://en.wikipedia.org/wiki/EIA-608
*/
void eia608_caption(const char *utf8_str, float duration_secs, eia608_captionparms_t *parms);
void eia608_caption_prepare(eia608_channel_t cc, const char *utf8_str, eia608_captionparms_t *parms);

/**
* @brief Show a caption that was previously prepared with #eia608_caption
*
* By default, #eia608_caption will prepare the caption and display it right
* away. Transmitting a caption can take a non negligible amount of time
* (it is about 1 second every 60 characters). If you need perfect syncing,
* you can first prepare the caption and keep it hidden, by calling
* #eia608_caption with the \p hidden parameter set to true in \p parms.
* Then, when you are ready to display the caption, call this function.
* This shows a caption that was prepared by #eia608_caption_prepare. The caption
* will be displayed on the screen for the specified duration, and then hidden.
*
* @param cc Channel in which the caption was prepared.
* @param duration_secs The duration in seconds to display the caption
*/
void eia608_caption_show(eia608_channel_t cc);
void eia608_caption_show(eia608_channel_t cc, float duration_secs);

#ifdef __cplusplus
}
Expand Down
74 changes: 43 additions & 31 deletions src/eia608.c
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Original file line number Diff line number Diff line change
Expand Up @@ -16,9 +16,6 @@
#include <assert.h>
#include <string.h>

#define EIA608_NOP 0x8080 ///< NOP filler (already including parity)
#define EIA608_EDM 0x942C ///< Erase Display Memory

#define SIG_ON 0x808080FF ///< IRE 50 (50% intensity)
#define SIG_OFF 0x00000000 ///< IRE 0

Expand Down Expand Up @@ -76,8 +73,9 @@ static void linebuffer_init(surface_t *lb)
static void linebuffer_write(surface_t *lb, uint16_t data)
{
uint32_t *buffer = lb->buffer;
buffer += SIGW_BLANK * SIGW_SCALE; // skip the blank part
buffer += SIGW_BLANK; // skip the blank part
buffer += SIGW_LEADIN * SIGW_SCALE; // skip the leadin part
data = (data << 8) | (data >> 8);
for (int i=0; i<16; i++) {
for (int j=0; j<SIGW_BIT; j++)
buffer = linebuffer_write_bit(buffer, data & 1);
Expand Down Expand Up @@ -132,20 +130,28 @@ static void recalc_parms(void)

static void __eia608_interrupt(void)
{
// Fetch the data from the ring buffer (or the NOP filler if empty)
uint16_t data;

if (force_clear_timer && --force_clear_timer == 0)
data = EIA608_EDM;
else if (rb_rpos == rb_wpos) {
data = EIA608_NOP;
} else {
data = ring_buffer[rb_rpos];
rb_rpos = (rb_rpos + 1) % RING_BUFFER_SIZE;
}
static int framecounter = 0; ++framecounter;

// We need to update the linebuffer at 30 Hz, so every
// other frame. Even if the display is interlaced, it doesn't
// really matter *which* field we do the update, as we emit
// the signal on both anyway.
if (framecounter & 1) {
// Fetch the data from the ring buffer (or the NOP filler if empty)
uint16_t data;

if (force_clear_timer && --force_clear_timer < 2) {
data = EIA608_CC1_EDM;
} else if (rb_rpos == rb_wpos) {
data = EIA608_NOP;
} else {
data = ring_buffer[rb_rpos];
rb_rpos = (rb_rpos + 1) % RING_BUFFER_SIZE;
}

// Draw the data into the linebuffer
linebuffer_write(&linebuffer, data);
// Draw the data into the linebuffer
linebuffer_write(&linebuffer, data);
}

// The VI should still be drawing the line *before* the one that we want
// to draw on. If we're not there, it means that the interrupt was late,
Expand All @@ -166,8 +172,8 @@ static void __eia608_interrupt(void)
// Wait for the line to match the one we're expecting
while ((*VI_V_CURRENT|1) != sigparms.v_line_start) {}

// We are not in hblank. Quickly switch VI configuration to draw the
// linebuffer
// We are now in hblank. Quickly switch VI configuration to draw the
// linebuffer.
*VI_ORIGIN = PhysicalAddr(linebuffer.buffer);
*VI_WIDTH = linebuffer.width;
*VI_CTRL = sigparms.reg_ctrl;
Expand Down Expand Up @@ -234,14 +240,15 @@ static uint8_t odd_parity(uint8_t value)

bool eia608_write_raw(uint16_t data, bool calc_parity)
{
debugf("EIA-608: %04X\n", data);
int next = (rb_wpos + 1) % RING_BUFFER_SIZE;
if (next == rb_rpos)
return false;

if (calc_parity)
data = odd_parity(data) | (odd_parity(data >> 8) << 8);

ring_buffer[rb_wpos] = (data >> 8) | (data << 8);
ring_buffer[rb_wpos] = data;
rb_wpos = next;
return true;
}
Expand Down Expand Up @@ -422,15 +429,14 @@ static uint32_t eia608_encode_char(const char **utf8_str)
return 0;
}

void eia608_caption(const char *utf8_str, float duration_secs, eia608_captionparms_t *parms)
void eia608_caption_prepare(eia608_channel_t cc, const char *utf8_str, eia608_captionparms_t *parms)
{
// EIA-608 POP-ON mode can only hold up to three lines of 32 characters each
enum { MAX_ROWS = 4 };

eia608_captionparms_t _default = {0};
if (parms == NULL) parms = &_default;

eia608_channel_t cc = parms->cc ? parms->cc : EIA608_CC1;
int first_row = parms->row ? parms->row : 11;

uint32_t buffer[32*MAX_ROWS+8];
Expand All @@ -441,8 +447,8 @@ void eia608_caption(const char *utf8_str, float duration_secs, eia608_captionpar

// Convert the input string from UTF-8 into EIA-608 16-bit characters.
for (int i = 0; i < sizeof(buffer)/2; i++) {
if (*utf8_str == 0) break;
uint16_t ch = eia608_encode_char(&utf8_str);
if (*utf8_str == 0) break;
uint32_t ch = eia608_encode_char(&utf8_str);
if (ch > 0x100 && cc == EIA608_CC2) ch |= 0x8000;
if (ch == 0) continue;
buffer[buf_len++] = ch;
Expand All @@ -468,6 +474,13 @@ void eia608_caption(const char *utf8_str, float duration_secs, eia608_captionpar
wrap = ch;
}

// Empty line, just skip it (or stop if we're done)
if (ch == 0) {
if (buf_idx >= buf_len) break;
buf_idx++;
continue;
}

// We need to wrap if we reached 32 chars and there are more
if (ch == 32 && buf_idx+ch < buf_len)
ch = wrap;
Expand All @@ -486,7 +499,7 @@ void eia608_caption(const char *utf8_str, float duration_secs, eia608_captionpar
// Split the token into 1, 2, or 1+2 byte values
uint16_t single = 0, pair = 0;
if (token >> 16) {
single = token >> 8;
single = token >> 16;
pair = token & 0xffff;
} else if (token >> 8) {
pair = token;
Expand Down Expand Up @@ -524,15 +537,14 @@ void eia608_caption(const char *utf8_str, float duration_secs, eia608_captionpar

// Move to the next line
first_row++;
utf8_str += wrap+1;
}

// Emit end caption command (swap buffers)
if (!parms->hidden)
eia608_caption_show(cc);
// Skip wrapping character
buf_idx++;
}
}

void eia608_caption_show(eia608_channel_t cc)
void eia608_caption_show(eia608_channel_t cc, float duration_secs)
{
eia608_write_ctrl_raw(cc == EIA608_CC1 ? EIA608_CC1_EOC : EIA608_CC2_EOC);
force_clear_timer = duration_secs * 30;
}

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