Update assert and error to be interrupt safe

Add printf functions intended for errors which are safe to call from
interrupts.  Update assert and error to use this function.

hal/api/mbed_interface.h

@@ -16,6 +16,8 @@
 #ifndef MBED_INTERFACE_H
 #define MBED_INTERFACE_H
 
+#include <stdarg.h>
+
 #include "device.h"
 
 /* Mbed interface mac address
@@ -107,6 +109,20 @@ void mbed_mac_address(char *mac);
  */
 void mbed_die(void);
 
+/** Print out an error message.  This is typically called when
+ * hanlding a crash.
+ *
+ * @Note Synchronization level: Interrupt safe
+ */
+void mbed_error_printf(const char* format, ...);
+
+/** Print out an error message.  Similar to mbed_error_printf
+ * but uses a va_list.
+ *
+ * @Note Synchronization level: Interrupt safe
+ */
+void mbed_error_vfprintf(const char * format, va_list arg);
+
 #ifdef __cplusplus
 }
 #endif

hal/common/assert.c

@@ -16,17 +16,12 @@
 #include "mbed_assert.h"
 #include "device.h"
 
-#if DEVICE_STDIO_MESSAGES
-#include <stdio.h>
-#endif
-
-#include <stdlib.h>
 #include "mbed_interface.h"
+#include "critical.h"
 
 void mbed_assert_internal(const char *expr, const char *file, int line)
 {
-#if DEVICE_STDIO_MESSAGES
-    fprintf(stderr, "mbed assertation failed: %s, file: %s, line %d \n", expr, file, line);
-#endif
+    core_util_critical_section_enter();
+    mbed_error_printf("mbed assertation failed: %s, file: %s, line %d \n", expr, file, line);
     mbed_die();
 }

hal/common/board.c

@@ -13,11 +13,18 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+#include <stdio.h>
 #include "gpio_api.h"
 #include "wait_api.h"
 #include "toolchain.h"
 #include "mbed_interface.h"
 #include "critical.h"
+#include "serial_api.h"
+
+#if DEVICE_SERIAL
+extern int stdio_uart_inited;
+extern serial_t stdio_uart;
+#endif
 
 WEAK void mbed_die(void) {
 #if !defined (NRF51_H) && !defined(TARGET_EFM32)
@@ -58,3 +65,27 @@ WEAK void mbed_die(void) {
         wait_ms(150);
     }
 }
+
+void mbed_error_printf(const char* format, ...) {
+    va_list arg;
+    va_start(arg, format);
+    mbed_error_vfprintf(format, arg);
+    va_end(arg);
+}
+
+void mbed_error_vfprintf(const char * format, va_list arg) {
+#if DEVICE_SERIAL
+    core_util_critical_section_enter();
+    char buffer[128];
+    int size = vsprintf(buffer, format, arg);
+    if (size > 0) {
+        if (!stdio_uart_inited) {
+        serial_init(&stdio_uart, STDIO_UART_TX, STDIO_UART_RX);
+        }
+        for (int i = 0; i < size; i++) {
+            serial_putc(&stdio_uart, buffer[i]);
+        }
+    }
+    core_util_critical_section_exit();
+#endif
+}

hal/common/error.c

@@ -23,11 +23,9 @@
 #endif
 
 WEAK void error(const char* format, ...) {
-#if DEVICE_STDIO_MESSAGES
     va_list arg;
     va_start(arg, format);
-    vfprintf(stderr, format, arg);
+    mbed_error_vfprintf(format, arg);
     va_end(arg);
-#endif
     exit(1);
 }