srd: Support for one or more optional probes.

In the protocol decoder you always get all required probes, then _all_
optional probes in the list of probes in the decode() call.

Example:

 (r1, r2, r3, o1, o2, o3, o4) = pins

In this case r1-r3 are required probes, o1-o4 are optional probes.
However, the value of valid/used/specified probes will be 0 or 1,
whereas the value of probes that were not specified/assigned by the user
will be (at the moment) 42.

The PD can check for a valid probe like this:

  if p in (0, 1):
    ...

Or check for an invalid probe:

  if (p > 1):
    ...

The value of 42 could change to be -1 or None later.

1 files changed, 16 insertions, 1 deletions

diff --git a/type_logic.c b/type_logic.c
index b284ebf..098e34d 100644
--- a/type_logic.c
+++ b/type_logic.c
@@ -45,11 +45,26 @@ static PyObject *srd_logic_iternext(PyObject *self)
 	 * Convert the bit-packed sample to an array of bytes, with only 0x01
 	 * and 0x00 values, so the PD doesn't need to do any bitshifting.
 	 */
+
+	/* Get probe bits into the 'sample' variable. */
 	memcpy(&sample,
 	       logic->inbuf + logic->itercnt * logic->di->data_unitsize,
 	       logic->di->data_unitsize);
-	for (i = 0; i < logic->di->dec_num_probes; i++)
+
+	/* All probe values (required + optional) are pre-set to 42. */
+	memset(probe_samples, 42, logic->di->dec_num_probes);
+	/* TODO: None or -1 in Python would be better. */
+
+	/*
+	 * Set probe values of specified/used probes to their resp. values.
+	 * Unused probe values (those not specified by the user) remain at 42.
+	 */
+	for (i = 0; i < logic->di->dec_num_probes; i++) {
+		/* A probemap value of -1 means "unused optional probe". */
+		if (logic->di->dec_probemap[i] == -1)
+			continue;
 		probe_samples[i] = sample & (1 << logic->di->dec_probemap[i]) ? 1 : 0;
+	}
 
 	/* Prepare the next samplenum/sample list in this iteration. */
 	py_samplenum =