cardem: show detailed reset cause

this helps detecting when a reset was due to the watchdog

Change-Id: I2d59c2f2c8fe9e559eddfafacf25879263ef81ff
diff --git a/firmware/apps/cardem/main.c b/firmware/apps/cardem/main.c
index ae46794..7d65c7e 100644
--- a/firmware/apps/cardem/main.c
+++ b/firmware/apps/cardem/main.c
@@ -157,11 +157,25 @@
 		"SIMtrace2 firmware " GIT_VERSION " (C) 2010-2016 by Harald Welte\n\r"
 		"=============================================================================\n\r");
 
+#if (TRACE_LEVEL >= TRACE_LEVEL_INFO)
 	TRACE_INFO("Chip ID: 0x%08x (Ext 0x%08x)\n\r", CHIPID->CHIPID_CIDR, CHIPID->CHIPID_EXID);
 	TRACE_INFO("Serial Nr. %08x-%08x-%08x-%08x\n\r",
 		   g_unique_id[0], g_unique_id[1],
 		   g_unique_id[2], g_unique_id[3]);
-	TRACE_INFO("Reset Cause: 0x%x\n\r", (RSTC->RSTC_SR & RSTC_SR_RSTTYP_Msk) >> RSTC_SR_RSTTYP_Pos);
+	uint8_t reset_cause = (RSTC->RSTC_SR & RSTC_SR_RSTTYP_Msk) >> RSTC_SR_RSTTYP_Pos;
+	static const char* reset_causes[] = {
+		"general reset (first power-up reset)",
+		"backup reset (return from backup mode)",
+		"watchdog reset (watchdog fault occurred)",
+		"software reset (processor reset required by the software)",
+		"user reset (NRST pin detected low)",
+	};
+	if (reset_cause < ARRAY_SIZE(reset_causes)) {
+		TRACE_INFO("Reset Cause: %s\n\r", reset_causes[reset_cause]);
+	} else {
+		TRACE_INFO("Reset Cause: 0x%x\n\r", (RSTC->RSTC_SR & RSTC_SR_RSTTYP_Msk) >> RSTC_SR_RSTTYP_Pos);
+	}
+#endif
 
 	board_main_top();