trone: added support for WHOAMI register

src/drivers/trone/trone.cpp

@@ -79,6 +79,9 @@
 /* TRONE Registers addresses */
 
 #define TRONE_MEASURE_REG	0x00		/* Measure range register */
+#define TRONE_WHO_AM_I_REG  0x01        /* Who am I test register */
+#define TRONE_WHO_AM_I_REG_VAL 0xA1
+
  
 /* Device limits */
 #define TRONE_MIN_DISTANCE (0.20f)
@@ -308,7 +311,20 @@ out:
 int
 TRONE::probe()
 {
+	uint8_t who_am_i=0;
+
+	const uint8_t cmd = TRONE_WHO_AM_I_REG;
+	if (transfer(&cmd, 1, &who_am_i, 1) == OK && who_am_i == TRONE_WHO_AM_I_REG_VAL) {
+		// it is responding correctly to a WHO_AM_I
 		return measure();
+	}
+
+	debug("WHO_AM_I byte mismatch 0x%02x should be 0x%02x\n",
+		(unsigned)who_am_i,
+		TRONE_WHO_AM_I_REG_VAL);
+
+	// not found on any address
+	return -EIO;
 }
 
 void
@@ -643,7 +659,6 @@ TRONE::cycle()
 		 * Is there a collect->measure gap?
 		 */
 		if (_measure_ticks > USEC2TICK(TRONE_CONVERSION_INTERVAL)) {
-
 			/* schedule a fresh cycle call when we are ready to measure again */
 			work_queue(HPWORK,
 				&_work,