Time-scale calculation routines

Collaboration diagram for Time-scale calculation routines:

Topics
	Time-scale units

Macros
#define	SSTVENC_TS_INFINITE   UINT32_MAX

Functions
uint64_t	sstvenc_ts_unit_scale (uint8_t unit)
uint32_t	sstvenc_ts_clamp_samples (uint64_t samples)
uint32_t	sstvenc_ts_unit_to_samples (double time, uint32_t sample_rate, uint8_t unit)
double	sstvenc_ts_samples_to_unit (uint32_t samples, uint32_t sample_rate, uint8_t unit)

Detailed Description

Conversion between discrete samples and real-time. SSTV timings are given in real-world seconds (actually, nanoseconds) as time units but we need to know what that is in the number of discrete samples. There is rounding applied to handle fractional samples.

Time periods down to nanosecond precision may be specified.

Conversion between discrete samples and real-time. SSTV timings are given in real-world seconds (actually, nanoseconds) as time units but we need to know what that is in the number of discrete samples. There is rounding applied to handle fractional samples.

Time periods down to nanosecond precision may be specified.

Macro Definition Documentation

SSTVENC_TS_INFINITE

#define SSTVENC_TS_INFINITE   UINT32_MAX

Infinite time scale. We set this to the maximum number of samples, which at 48kHz sample rates, equates to about a day.

Definition at line 28 of file timescale.h.

Referenced by sstvenc_ts_clamp_samples(), sstvenc_ts_samples_to_unit(), and sstvenc_ts_unit_to_samples().

Function Documentation

sstvenc_ts_clamp_samples()

uint32_t sstvenc_ts_clamp_samples

(

uint64_t

samples

)

Clamp the given number of samples to a safe maximum. If the value is greater than that supported by a uint32_t data type, it is clamped to SSTVENC_TS_INFINITE.

Parameters

[in]

samples

Unclamped number of samples.

Returns

Clamped number of samples.

Definition at line 38 of file timescale.c.

                                                    {
        if (samples > UINT32_MAX) {
                return SSTVENC_TS_INFINITE;
        } else {
                return samples;
        }
}

References SSTVENC_TS_INFINITE.

Referenced by sstvenc_ts_unit_to_samples().

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sstvenc_ts_samples_to_unit()

double sstvenc_ts_samples_to_unit	(	uint32_t	samples,
		uint32_t	sample_rate,
		uint8_t	unit )

Convert the given number of samples to a time period in the specified unit.

Parameters

[in]	samples	The number of samples being measured.
[in]	sample_rate	The sample rate in hertz being used for the discrete timebase.
[in]	unit	The time unit desired, see Time-scale units

Returns

The time period represented by the given number of samples in the given time unit.

Return values

INFINITY

Infinite number of samples is represented.

Definition at line 57 of file timescale.c.

                                                {
        if (samples == SSTVENC_TS_INFINITE) {
                return INFINITY;
        } else {
                uint64_t n = samples * sstvenc_ts_unit_scale(unit);
                return ((double)n) / ((double)sample_rate);
        }
}

References SSTVENC_TS_INFINITE, and sstvenc_ts_unit_scale().

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sstvenc_ts_unit_scale()

uint64_t sstvenc_ts_unit_scale

(

uint8_t

unit

)

Obtain the scaling factor to convert 1 second of time to the given unit.

Parameters

[in]

unit

The time scale of interest. Time-scale units

Returns

The number of specified time units in one second.

Definition at line 22 of file timescale.c.

                                             {
        switch (unit) {
        case SSTVENC_TS_UNIT_SECONDS:
                return 1;
        case SSTVENC_TS_UNIT_MILLISECONDS:
                return 1000;
        case SSTVENC_TS_UNIT_MICROSECONDS:
                return 1000000;
        case SSTVENC_TS_UNIT_NANOSECONDS:
                return 1000000000;
        default:
                /* Not supported */
                assert(0);
        }
}

References SSTVENC_TS_UNIT_MICROSECONDS, SSTVENC_TS_UNIT_MILLISECONDS, SSTVENC_TS_UNIT_NANOSECONDS, and SSTVENC_TS_UNIT_SECONDS.

Referenced by sstvenc_sequencer_exec_set_ts(), sstvenc_ts_samples_to_unit(), and sstvenc_ts_unit_to_samples().

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sstvenc_ts_unit_to_samples()

uint32_t sstvenc_ts_unit_to_samples	(	double	time,
		uint32_t	sample_rate,
		uint8_t	unit )

Convert the given time period to the number of units.

Parameters

[in]	time	The number of time units being converted.
[in]	sample_rate	The sample rate in hertz being used for the discrete timebase.
[in]	unit	The time unit being measured, see Time-scale units

Returns

The number of samples needed for that time period.

Return values

SSTVENC_TS_INFINITE

Time period is too long to represent.

Definition at line 46 of file timescale.c.

                                                  {
        if (time == INFINITY) {
                return SSTVENC_TS_INFINITE;
        } else {
                return sstvenc_ts_clamp_samples(
                    ((uint64_t)((time * sample_rate) + 0.5))
                    / sstvenc_ts_unit_scale(unit));
        }
}

References sstvenc_ts_clamp_samples(), SSTVENC_TS_INFINITE, and sstvenc_ts_unit_scale().

Referenced by sstvenc_cw_init(), sstvenc_modulator_next_tone(), sstvenc_ps_init(), sstvenc_ps_reset(), and sstvenc_sequencer_begin_silence().

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