Fix frequency verb invalid frequency behavior

The frequency verb was not checking if a frequency corresponds to the
frequency band step the binding provides to users, add logic to do so
and return an error if the frequency is invalid.  While this is a
change in behavior, it is believe it should not impact users, as the
binding is intended to reflect user facing radio application usage.

Additional tweaks:
- fix error invalid frequency error message in reply JSON.
- add the same band limit checks to the null implementation's
  frequency setting function that the other implementations do.
- fix a couple of issues in README.md; the "rds" verb was missing,
  and the value key name for the "frequency" event was incorrect.

Bug-AGL: SPEC-3620

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I2adfc10448546264110f6d854f02d677087f1e47

3 files changed, 28 insertions, 7 deletions

diff --git a/README.md b/README.md
index 2155649..90184b7 100644
--- a/README.md
+++ b/README.md
@@ -21,12 +21,13 @@ respective audio stream.
 | scan_start         | start scanning for station                  | *Request:* {"direction": "forward" or "backward"}              |
 | scan_stop          | stop scanning for station                   |                                                                |
 | stereo_mode        | get/set stereo or mono mode                 | *Request:* {"value": "stereo" or "mono"}                       |
+| rds                | get current RDS data                        |                                                                |
 
 ## Events
 
 ### frequency Event JSON Response
 
-JSON response has a single field **frequency** which is the currently tuned frequency.
+JSON response has a single field **value** which is the currently tuned frequency.
 
 ### station_found Event JSON Response
 
diff --git a/binding/radio-binding.c b/binding/radio-binding.c
index 34eb53e..45e8ecb 100644
--- a/binding/radio-binding.c
+++ b/binding/radio-binding.c
@@ -90,11 +90,26 @@ static void frequency(afb_req_t request)
 
 	if(value) {
 		char *p;
+		radio_band_t band;
+		uint32_t min_frequency;
+		uint32_t max_frequency;
+		uint32_t step;
+
 		frequency = (uint32_t) strtoul(value, &p, 10);
 		if(frequency && *p == '\0') {
+			band = radio_impl_ops->get_band();
+			min_frequency = radio_impl_ops->get_min_frequency(band);
+			max_frequency = radio_impl_ops->get_max_frequency(band);
+			step = radio_impl_ops->get_frequency_step(band);
+			if(frequency < min_frequency ||
+			   frequency > max_frequency ||
+			   (frequency - min_frequency) % step) {
+				afb_req_reply(request, NULL, "failed", "Invalid frequency");
+				return;
+			}
 			radio_impl_ops->set_frequency(frequency);
 		} else {
-			afb_req_reply(request, NULL, "failed", "Invalid scan direction");
+			afb_req_reply(request, NULL, "failed", "Invalid frequency");
 			return;
 		}
 	}
@@ -104,11 +119,12 @@ static void frequency(afb_req_t request)
 	afb_req_reply(request, ret_json, NULL, NULL);
 }
 
-/* @brief Get RDS information
-*
-* @param afb_req_t : an afb request structure
-*
-*/
+/*
+ * @brief Get RDS information
+ *
+ * @param afb_req_t : an afb request structure
+ *
+ */
 static void rds(afb_req_t request)
 {
 	json_object *ret_json;
diff --git a/binding/radio_impl_null.c b/binding/radio_impl_null.c
index 8c28bca..a90835b 100644
--- a/binding/radio_impl_null.c
+++ b/binding/radio_impl_null.c
@@ -120,6 +120,10 @@ static uint32_t null_get_frequency(void)
 
 static void null_set_frequency(uint32_t frequency)
 {
+	if(frequency < known_fm_band_plans[bandplan].min ||
+	   frequency > known_fm_band_plans[bandplan].max)
+		return;
+
 	current_frequency = frequency;
 
 	if(freq_callback)