rds: implement more robust PS/RT parsing

Our current PS and RT parser is very strict: it requires
all segments to be received in order. This is too strong
of an assumption even when the reception in good, particularly
for long RT messages. This parser handles segments in any order
and completes a message only when all segments are present. To
avoid keeping obsolete segments, each segment has an associated
timeout and is trashed if not updated for a certain period.

Change-Id: I79841bb5ab1f838c7702d8281044e226f6510199
Reviewed-on: http://gerrit.rockbox.org/237
Tested-by: Bertrik Sikken <bertrik@sikken.nl>
Reviewed-by: Bertrik Sikken <bertrik@sikken.nl>

1 files changed, 32 insertions, 19 deletions

diff --git a/firmware/drivers/rds.c b/firmware/drivers/rds.c
index eb14cfb009..df766094de 100644
--- a/firmware/drivers/rds.c
+++ b/firmware/drivers/rds.c
@@ -22,20 +22,27 @@
 #include <stdint.h>
 #include <string.h>
 #include <strlcpy.h>
+#include <kernel.h>
 #include "rds.h"
 #include "time.h"
 
+// timeout before segment obsolescence
+#define PS_SEGMENT_TIMEOUT  (HZ / 2)
+#define RT_SEGMENT_TIMEOUT  (10 * HZ)
+
 /* programme identification */
 static uint16_t pi_code;
 static uint16_t pi_last;
 /* program service name */
 static char ps_data[9];
 static char ps_copy[9];
-static int ps_segment;
+static long ps_segment_timeout[4];
+static int ps_segment;// bitmap of received segments
 /* radio text */
 static char rt_data[65];
 static char rt_copy[65];
-static int rt_segment;
+static long rt_segment_timeout[16];
+static int rt_segment;// bitmap of received segments
 static int rt_abflag;
 /* date/time */
 static time_t ct_data;
@@ -95,22 +102,21 @@ static bool handle_group0(uint16_t data[4])
 {
     int segment, pos;
 
-    segment = data[1] & 3;
+    /* remove obsolete segments */
+    for(int i = 0; i < 4; i++)
+        if(TIME_AFTER(current_tick, ps_segment_timeout[i]))
+            ps_segment &= ~(1 << i);
 
-    /* reset parsing if not in expected order */
-    if (segment != ps_segment) {
-        ps_segment = 0;
-        if (segment != 0) {
-            return false;
-        }
-    }
+    segment = data[1] & 3;
 
     /* store data */
     pos = segment * 2;
     ps_data[pos++] = (data[3] >> 8) & 0xFF;
     ps_data[pos++] = (data[3] >> 0) & 0xFF;
-    if (++ps_segment == 4) {
-        ps_data[pos] = '\0';
+    ps_segment |= 1 << segment;
+    ps_segment_timeout[segment] = current_tick + PS_SEGMENT_TIMEOUT;
+    if (ps_segment == 0xf) {
+        ps_data[8] = '\0';
         if (strcmp(ps_copy, ps_data) != 0) {
             /* we got an updated message */
             strcpy(ps_copy, ps_data);
@@ -143,21 +149,25 @@ static bool handle_group2(uint16_t data[4])
 {
     int abflag, segment, version, pos;
     bool done;
+
+    /* remove obsolete segments */
+    for(int i = 0; i < 16; i++)
+        if(TIME_AFTER(current_tick, rt_segment_timeout[i]))
+            rt_segment &= ~(1 << i);
     
-    /* reset parsing if not in expected order */
+    /* reset parsing if the message type changed */
     abflag = (data[1] >> 4) & 1;
     segment = data[1] & 0xF;
-    if ((abflag != rt_abflag) || (segment != rt_segment)) {
+    if (abflag != rt_abflag) {
         rt_abflag = abflag;
         rt_segment = 0;
-        if (segment != 0) {
-            return false;
-        }
     }
 
+    rt_segment |= 1 << segment;
+    rt_segment_timeout[segment] = current_tick + RT_SEGMENT_TIMEOUT;
+
     /* store data */
     version = (data[1] >> 11) & 1;
-    done = false;
     if (version == 0) {
         pos = segment * 4;
         done = done || handle_rt(pos++, (data[2] >> 8) & 0xFF);
@@ -169,7 +179,10 @@ static bool handle_group2(uint16_t data[4])
         done = done || handle_rt(pos++, (data[3] >> 8) & 0xFF);
         done = done || handle_rt(pos++, (data[3] >> 0) & 0xFF);
     }
-    if ((++rt_segment == 16) || done) {
+    /* there are two cases for completion:
+     * - we got all 16 segments
+     * - we found a end of line AND we got all segments before it */
+    if (rt_segment == 0xffff || (done && rt_segment == (1 << segment) - 1)) {
         rt_data[pos] = '\0';
         if (strcmp(rt_copy, rt_data) != 0) {
             /* we got an updated message */