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input/csv: add support for timestamp columns, auto detect samplerate 

Accept 't' format specs for timestamp columns. Automatically derive the
samplerate from input data when timestamps are available and the user
did not provide a rate. Stick with a simple approach for robustness
since automatic detection is easy to override when it fails. This
feature is mostly about convenience.
This commit is contained in:
Gerhard Sittig 2019-10-18 01:11:26 +02:00
parent fc3b42e93a
commit 7e4e65bf65
1 changed files with 118 additions and 7 deletions
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125
src/input/csv.c
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@ -43,11 +43,12 @@
* single-bit logic), and an optional bit count (translating to: logic
* channels communicated in that column). The 'a' format marks analog
* data, an optionally following number is the digits count (resolution).
* This "column_formats" option is most versatile, other forms of
* specifying the column layout only exist for backwards compatibility,
* and are rather limited. They exclusively support logic input data in
* strictly adjacent columns, with further constraints on column layout
* for multi-bit data.
* The 't' format marks timestamp values, which could help in automatic
* determination of the input stream's samplerate. This "column_formats"
* option is most versatile, other forms of specifying the column layout
* only exist for backwards compatibility, and are rather limited. They
* exclusively support logic input data in strictly adjacent columns,
* with further constraints on column layout for multi-bit data.
*
* single_column: Specifies the column number which contains the logic data
* for single-column mode. All logic data is taken from several bits
@ -116,6 +117,14 @@
* - ... -I csv:column_formats=*a6 ...
* Each column contains an analog value with six significant digits
* after the decimal period.
* - ... -I csv:column_formats=t,2a ...
* The first column contains timestamps, the next two columns contain
* analog values. The capture's samplerate could get determined from
* the timestamp values if not provided by the user by means of the
* 'samplerate' option. This assumes a mere number in units of seconds,
* and equidistant rows, there is no fancy support for textual unit
* suffixes nor gaps in the stream of samples nor other non-linearity,
* just '-' ignore the column if the format is not supported).
*/
/*
@ -153,6 +162,7 @@ enum single_col_format {
FORMAT_HEX, /* Hex digits for a set of bits. */
FORMAT_OCT, /* Oct digits for a set of bits. */
FORMAT_ANALOG, /* Floating point number for an analog channel. */
FORMAT_TIME, /* Timestamps. */
};
static const char *col_format_text[] = {
@ -161,6 +171,7 @@ static const char *col_format_text[] = {
[FORMAT_HEX] = "hexadecimal",
[FORMAT_OCT] = "octal",
[FORMAT_ANALOG] = "analog",
[FORMAT_TIME] = "timestamp",
};
static const char col_format_char[] = {
@ -169,6 +180,7 @@ static const char col_format_char[] = {
[FORMAT_HEX] = 'x',
[FORMAT_OCT] = 'o',
[FORMAT_ANALOG] = 'a',
[FORMAT_TIME] = 't',
};
static gboolean format_is_ignore(enum single_col_format fmt)
@ -186,6 +198,11 @@ static gboolean format_is_analog(enum single_col_format fmt)
return fmt == FORMAT_ANALOG;
}
static gboolean format_is_timestamp(enum single_col_format fmt)
{
return fmt == FORMAT_TIME;
}
struct column_details {
size_t col_nr;
enum single_col_format text_format;
@ -198,8 +215,9 @@ struct column_details {
struct context {
gboolean started;
/* Current selected samplerate. */
/* Current samplerate, optionally determined from input data. */
uint64_t samplerate;
double prev_timestamp;
gboolean samplerate_sent;
/* Number of channels. */
@ -499,6 +517,9 @@ static int split_column_format(const char *spec,
case 'a':
format_code = FORMAT_ANALOG;
break;
case 't':
format_code = FORMAT_TIME;
break;
default: /* includes NUL */
return SR_ERR_ARG;
}
@ -889,6 +910,95 @@ static int parse_analog(const char *column, struct context *inc,
return SR_OK;
}
/**
* @brief Parse a timestamp text, auto-determine samplerate.
*
* @param[in] column The input text, a floating point number.
* @param[in] inc The input module's context.
* @param[in] details The column processing details.
*
* @retval SR_OK Success.
* @retval SR_ERR Invalid input data (empty, or format error).
*
* This routine attempts to automatically determine the input data's
* samplerate from text rows' timestamp values. Only simple formats are
* supported, user provided values always take precedence.
*/
static int parse_timestamp(const char *column, struct context *inc,
const struct column_details *details)
{
double ts, rate;
int ret;
if (!format_is_timestamp(details->text_format))
return SR_ERR_BUG;
/*
* Implementor's notes on timestamp interpretation. Use a simple
* approach for improved maintainability which covers most cases
* of input data. There is not much gain in adding complexity,
* users can easily provide the rate when auto-detection fails.
* - Bail out if samplerate is known already.
* - Try to interpret the timestamp (simple float conversion).
* If conversion fails then clear all previous knowledge and
* bail out (non-fatal, perhaps warn). Silently ignore values
* of zero since those could be silent fails -- assume that
* genuine data contains at least two adjacent rows with useful
* timestamps for the feature to work reliably. Annoying users
* with "failed to detect" messages is acceptable here, since
* users expecting the feature to work should provide useful
* data, and there are easy ways to disable the detection or
* ignore the column.
* - If there is no previous timestamp, keep the current value
* for later reference and bail out.
* - If a previous timestamp was seen, determine the difference
* between them, and derive the samplerate. Update internal
* state (the value automatically gets sent to the datafeed),
* and clear previous knowledge. Subsequent calls will ignore
* following input data (see above, rate is known).
*
* TODO Potential future improvements:
* - Prefer rationals over floats for improved precision and
* reduced rounding errors which result in odd rates.
* - Support other formats ("2 ms" or similar)?
*/
if (inc->samplerate)
return SR_OK;
ret = sr_atod_ascii(column, &ts);
if (ret != SR_OK)
ts = 0.0;
if (!ts) {
sr_warn("Cannot convert timestamp text %s in line %zu (or zero value).",
column, inc->line_number);
inc->prev_timestamp = 0.0;
return SR_OK;
}
if (!inc->prev_timestamp) {
sr_dbg("First timestamp value %g in line %zu.",
ts, inc->line_number);
inc->prev_timestamp = ts;
return SR_OK;
}
sr_dbg("Second timestamp value %g in line %zu.", ts, inc->line_number);
ts -= inc->prev_timestamp;
sr_dbg("Timestamp difference %g in line %zu.",
ts, inc->line_number);
if (!ts) {
sr_warn("Zero timestamp difference in line %zu.",
inc->line_number);
inc->prev_timestamp = ts;
return SR_OK;
}
rate = 1.0 / ts;
rate += 0.5;
rate = (uint64_t)rate;
sr_dbg("Rate from timestamp %g in line %zu.", rate, inc->line_number);
inc->samplerate = rate;
inc->prev_timestamp = 0.0;
return SR_OK;
}
/**
* @brief Parse routine which ignores the input text.
*
@ -913,6 +1023,7 @@ static const col_parse_cb col_parse_funcs[] = {
[FORMAT_OCT] = parse_logic,
[FORMAT_HEX] = parse_logic,
[FORMAT_ANALOG] = parse_analog,
[FORMAT_TIME] = parse_timestamp,
};
static int init(struct sr_input *in, GHashTable *options)
@ -1486,7 +1597,7 @@ enum option_index {
static struct sr_option options[] = {
[OPT_COL_FMTS] = {
"column_formats", "Column format specs",
"Specifies text columns data types: A comma separated list of [<cols>]<fmt>[<bits>] items, with - to ignore columns, x/o/b/l for logic data, a (and resolution) for analog data.",
"Specifies text columns data types: A comma separated list of [<cols>]<fmt>[<bits>] items, with - to ignore columns, x/o/b/l for logic data, a (and resolution) for analog data, t for timestamps.",
NULL, NULL,
},
[OPT_SINGLE_COL] = {