sys/can: improve SJW calculation

Author: kfessel

sys/can/device.c

@@ -581,16 +581,23 @@ int can_device_calc_bittiming(uint32_t clock, const struct can_bittiming_const *
     timing->phase_seg1 = tseg1 - timing->prop_seg;
     timing->phase_seg2 = tseg2;
 
-    if (!timing->sjw || !timing_const->sjw_max) {
+    if (!timing->sjw && !timing_const->sjw_max) {
+        /* fallback if sjw is unset and no device max value is known */
         timing->sjw = SJW;
     }
     else {
+        if (!timing->sjw) {
+            /* SJW shall not be bigger than phase segmet 2*/
+            timing->sjw = timing->phase_seg2;
+        }
+        if (timing->sjw > timing->phase_seg1) {
+            /* SJW shall not be bigger than phase segmet 1*/
+             timing->sjw = timing->phase_seg1;
+        }
         if (timing->sjw > timing_const->sjw_max) {
+            /* SJW shall not be bigger than its max value*/
             timing->sjw = timing_const->sjw_max;
         }
-        if (timing->sjw > tseg2) {
-            timing->sjw = tseg2;
-        }
     }
 
     timing->brp = best_brp;