fixup: set a default transceiver loop delay value for CI

sys/Kconfig

@@ -7,6 +7,7 @@
 menu "System"
 
 rsource "auto_init/Kconfig"
+rsource "can/Kconfig"
 rsource "chunked_ringbuffer/Kconfig"
 rsource "congure/Kconfig"
 rsource "debug_irq_disable/Kconfig"

sys/can/Kconfig

@@ -0,0 +1,36 @@
+menu "CAN"
+    depends on USEMODULE_CAN || USEMODULE_FDCAN
+
+menu "FD CAN"
+
+config FDCAN_DEVICE_SET_TRANSCEIVER_LOOP_DELAY
+    depends on USEMODULE_FDCAN
+    bool "FD CAN transceiver loop delay"
+    default n
+    help
+        Allow to set FD CAN Transceiver loop delay.
+
+config FDCAN_DEVICE_TRANSCEIVER_LOOP_DELAY
+    depends on FDCAN_DEVICE_SET_TRANSCEIVER_LOOP_DELAY
+    int "FD CAN transceiver loop delay value"
+    range 0 1000
+    default 0
+    help
+      This parameter defines the loop delay introduced by the CAN transceiver
+      during transmission. The loop delay represents the time taken for the
+      transmitted signal to be looped back to the CAN controller. This delay
+      is introduced by the physical transceiver circuitry and may vary
+      depending on the transceiver model and other physical factors.
+
+      The value is typically measured in nanoseconds and should be set
+      according to the specifications provided by the transceiver manufacturer.
+      A higher loop delay can affect the timing of CAN message transmissions
+      and may need to be adjusted in systems with tight timing requirements.
+
+      If unsure, leave this value as 0 or refer to the hardware documentation
+      for the correct delay value.
+
+
+endmenu # FD CAN
+
+endmenu # CAN

sys/can/device.c

@@ -40,9 +40,9 @@
  * The loop delay in CAN, especially in CAN FD with bitrate switching, affects synchronization due to increased data rates.
  * The unit is nanoseconds.
  */
-#ifndef CAN_DEVICE_DEFAULT_LOOP_DELAY
-#error "CAN_DEVICE_DEFAULT_LOOP_DELAY must be defined in the application's Makefile. This property can be found in the datasheet of the CAN transceiver in use. The unit is nanoseconds."
-#endif /* CAN_DEVICE_DEFAULT_LOOP_DELAY */
+#ifndef CONFIG_FDCAN_DEVICE_TRANSCEIVER_LOOP_DELAY
+#error "CONFIG_FDCAN_DEVICE_TRANSCEIVER_LOOP_DELAY must be defined. This property can be found in the datasheet of the CAN transceiver in use. The unit is nanoseconds."
+#endif /* CONFIG_FDCAN_DEVICE_TRANSCEIVER_LOOP_DELAY */
 #endif /* MODULE_FDCAN */
 
 #ifndef CAN_DEVICE_MSG_QUEUE_SIZE
@@ -248,7 +248,7 @@ static void *_can_device_thread(void *args)
 
 #if defined(MODULE_FDCAN)
     if (candev_dev->loop_delay == 0) {
-        candev_dev->loop_delay = CAN_DEVICE_DEFAULT_LOOP_DELAY;
+        candev_dev->loop_delay = CONFIG_FDCAN_DEVICE_TRANSCEIVER_LOOP_DELAY;
     }
     dev->loop_delay = candev_dev->loop_delay;
 #endif

tests/sys/conn_can/Makefile

@@ -47,3 +47,17 @@ ifneq (,$(filter native native64,$(BOARD)))
 else
 	CFLAGS += -DTHREAD_STACKSIZE_MAIN=2048
 endif
+
+# Loop delay
+ifneq (,$(filter fdcan,$(USEMODULE)))
+	ifneq (1,$(RIOT_CI_BUILD))
+		# Check your CAN transceiver datasheet to apply the good loop delay in nanoseconds.
+		# This configuration is mandatory if you are using CAN FD with bitrate switching.
+		# Can be configured here or through Kconfig
+		#CFLAGS += -DCONFIG_FDCAN_DEVICE_TRANSCEIVER_LOOP_DELAY=0
+
+	# Allow only a default value for CI
+	else
+		KCONFIG_ADD_CONFIG += $(CURDIR)/fdcan-ci.config
+	endif
+endif

tests/sys/conn_can/fdcan-ci.config

@@ -0,0 +1,2 @@
+CONFIG_FDCAN_DEVICE_SET_TRANSCEIVER_LOOP_DELAY=y
+CONFIG_FDCAN_DEVICE_TRANSCEIVER_LOOP_DELAY=0