[Layer1] Allow for some jitter in TDMA lost interrupt detection

The need for this has been pointed out by Sylvain...

diff --git a/src/target/firmware/layer1/sync.c b/src/target/firmware/layer1/sync.c
index 0c85c57..d4d2aed 100644 (file)
--- a/src/target/firmware/layer1/sync.c
+++ b/src/target/firmware/layer1/sync.c
@@ -176,8 +176,13 @@ void l1s_reset_hw(void)
        tpu_end_scenario();
 }
 
+/* Lost TDMA interrupt detection.  This works by starting a hardware timer
+ * that is clocked by the same master clock source (VCTCXO).  We expect
+ * 1875 timer ticks in the duration of a TDMA frame (5000 qbits / 1250 bits) */
+
 /* Timer for detecting lost IRQ */
 #define TIMER_TICKS_PER_TDMA   1875
+#define TIMER_TICK_JITTER      1
 
 static int last_timestamp;
 
@@ -189,7 +194,10 @@ static inline void check_lost_frame(void)
                last_timestamp += (4*TIMER_TICKS_PER_TDMA);
 
        diff = last_timestamp - timestamp;
-       if (diff != 1875)
+
+       /* allow for a bit of jitter */
+       if (diff < TIMER_TICKS_PER_TDMA - TIMER_TICK_JITTER ||
+           diff > TIMER_TICKS_PER_TDMA + TIMER_TICK_JITTER)
                printf("LOST!\n");
 
        last_timestamp = timestamp;