diff --git a/arch/arm/src/samdl/chip/saml_usart.h b/arch/arm/src/samdl/chip/saml_usart.h
index 78609072a7..2d364f6e70 100644
--- a/arch/arm/src/samdl/chip/saml_usart.h
+++ b/arch/arm/src/samdl/chip/saml_usart.h
@@ -253,6 +253,8 @@
 #define USART_SYNCBUSY_ENABLE        (1 << 1)  /* Bit 1:  SERCOM enable synchronization busy */
 #define USART_SYNCBUSY_CTRLB         (1 << 2)  /* Bit 2:  CTRLB synchronization busy */
 
+#define USART_SYNCBUSY_ALL           0x00000007
+
 /* Data register */
 
 #define USART_DATA_MASK              (0x1ff)   /* Bits 0-8: Data */
diff --git a/arch/arm/src/samdl/sam_lowputc.c b/arch/arm/src/samdl/sam_lowputc.c
index bb120ae2e8..26eec9108f 100644
--- a/arch/arm/src/samdl/sam_lowputc.c
+++ b/arch/arm/src/samdl/sam_lowputc.c
@@ -80,6 +80,22 @@
  * Private Functions
  ****************************************************************************/
 
+/****************************************************************************
+ * Name: sam_wait_synchronization
+ *
+ * Description:
+ *   Wait until the SERCOM USART reports that it is synchronized.
+ *
+ ****************************************************************************/
+
+#ifdef SAMDL_HAVE_USART
+static void
+sam_wait_synchronization(const struct sam_usart_config_s * const config)
+{
+  while (usart_syncbusy(config));
+}
+#endif
+
 /****************************************************************************
  * Name: sam_usart_configure
  *
diff --git a/arch/arm/src/samdl/sam_usart.h b/arch/arm/src/samdl/sam_usart.h
index a35923b7d3..528a15da8a 100644
--- a/arch/arm/src/samdl/sam_usart.h
+++ b/arch/arm/src/samdl/sam_usart.h
@@ -107,20 +107,21 @@ struct sam_usart_config_s
  * Name: sam_wait_synchronization
  *
  * Description:
- *   Wait until the SERCOM USART reports that it is synchronized.
+ *   Return true is the SERCOM USART reports that it is synchronizing.  This inline
+ *   function hides register differences between the SAMD20 and SAML21.
  *
  ***********************************************************************************/
 
 #ifdef SAMDL_HAVE_USART
-static inline void
-sam_wait_synchronization(const struct sam_usart_config_s * const config)
+static inline bool usart_syncbusy(const struct sam_usart_config_s * const config)
 {
 #if defined(CONFIG_ARCH_FAMILY_SAMD20)
-  while ((getreg16(config->base + SAM_USART_STATUS_OFFSET) & USART_STATUS_SYNCBUSY) != 0);
+  return ((getreg16(config->base + SAM_USART_STATUS_OFFSET) & USART_STATUS_SYNCBUSY) != 0);
 #elif defined(CONFIG_ARCH_FAMILY_SAML21)
-#  warning Need SAML21 synchronization logic
+  return ((getreg16(config->base + SAM_USART_SYNCBUSY_OFFSET) & USART_SYNCBUSY_ALL) != 0);
 #else
 #  error Unrecognized SAMD/L family
+  return false;
 #endif
 }
 #endif