input/chronovu_la8: claim responsibility for LA16 files, devel comments

The chronovu_la8 input module is capable of handling either file type,
generated by LA8 or LA16 vendor software. Automatic detection is not
available, but user provided channel counts work fine.

Adjust the input module's name and description, and claim support for
.kdt as well as .kd1 files.

Add developer notes on implementation details, the file content's
constraints, and potential future adjustment.

src/input/chronovu_la8.c

@@ -47,6 +47,36 @@
 #define CHRONOVU_LA8_HDRSIZE    (sizeof(uint8_t) + sizeof(uint32_t))
 #define CHRONOVU_LA8_FILESIZE   (CHRONOVU_LA8_DATASIZE + CHRONOVU_LA8_HDRSIZE)
 
+/*
+ * Implementation note:
+ *
+ * The .format_match() routine only checks the file size, but none of
+ * the header fields. Only little would be gained (only clock divider
+ * 0xff could get tested), but complexity would increase dramatically.
+ * Also the .format_match() routine is unlikely to receive large enough
+ * a buffer to include the header. Neither is the filename available to
+ * the .format_match() routine.
+ *
+ * There is no way to programmatically tell whether the file was created
+ * by LA8 or LA16 software, i.e. with 8 or 16 logic channels. If the
+ * filename was available, one might guess based on the file extension,
+ * but still would require user specs if neither of the known extensions
+ * were used or the input is fed from a pipe.
+ *
+ * The current input module implementation assumes that users specify
+ * the (channel count and) sample rate. Input data gets processed and
+ * passed along to the session bus, before the file "header" is seen.
+ * A future implementation could move channel creation from init() to
+ * receive() or end() (actually: a common routine called from those two
+ * routines), and could defer sample processing and feeding the session
+ * until the header was seen, including deferred samplerate calculation
+ * after having seen the header. But again this improvement depends on
+ * the availability of either the filename or the device type. Also note
+ * that applications then had to keep sending data to the input module's
+ * receive() routine until sufficient amounts of input data were seen
+ * including the header (see bug #1017).
+ */
+
 struct context {
 	gboolean started;
 	uint64_t samplerate;
@@ -214,9 +244,9 @@ static const struct sr_option *get_options(void)
 
 SR_PRIV struct sr_input_module input_chronovu_la8 = {
 	.id = "chronovu-la8",
-	.name = "ChronoVu LA8",
-	.desc = "ChronoVu LA8 native file format data",
-	.exts = (const char*[]){"kdt", NULL},
+	.name = "ChronoVu LA8/LA16",
+	.desc = "ChronoVu LA8/LA16 native file format data",
+	.exts = (const char*[]){"kdt", "kd1", NULL},
 	.metadata = { SR_INPUT_META_FILESIZE | SR_INPUT_META_REQUIRED },
 	.options = get_options,
 	.format_match = format_match,