* 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
* - ... -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).
*/
/*
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[] = {
[FORMAT_HEX] = "hexadecimal",
[FORMAT_OCT] = "octal",
[FORMAT_ANALOG] = "analog",
+ [FORMAT_TIME] = "timestamp",
};
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)
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;
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. */
case 'a':
format_code = FORMAT_ANALOG;
break;
+ case 't':
+ format_code = FORMAT_TIME;
+ break;
default: /* includes NUL */
return SR_ERR_ARG;
}
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.
*
[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)
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] = {
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