diff --git a/bacnet-stack/ports/bdk-atxx4-mstp/dlmstp.c b/bacnet-stack/ports/bdk-atxx4-mstp/dlmstp.c
index b9aac6c9..722eb563 100644
--- a/bacnet-stack/ports/bdk-atxx4-mstp/dlmstp.c
+++ b/bacnet-stack/ports/bdk-atxx4-mstp/dlmstp.c
@@ -370,7 +370,8 @@ static void MSTP_Send_Frame(
 {       /* number of bytes of data (up to 501) */
     uint8_t crc8 = 0xFF;        /* used to calculate the crc value */
     uint16_t crc16 = 0xFFFF;    /* used to calculate the crc value */
-    uint8_t buffer[8];  /* stores the header and data crc */
+    uint8_t buffer[8];  /* stores the header and header crc */
+    uint8_t buffer_crc[2];  /* stores the data crc */
     uint16_t i = 0;     /* used to calculate CRC for data */
 
     /* create the MS/TP header */
@@ -387,20 +388,24 @@ static void MSTP_Send_Frame(
     buffer[6] = LO_BYTE(data_len);
     crc8 = CRC_Calc_Header(buffer[6], crc8);
     buffer[7] = ~crc8;
-    rs485_turnaround_delay();
-    rs485_rts_enable(true);
-    rs485_bytes_send(buffer, 8);
-    /* send any data */
     if (data_len) {
         /* calculate CRC for any data */
         for (i = 0; i < data_len; i++) {
             crc16 = CRC_Calc_Data(data[i], crc16);
         }
         crc16 = ~crc16;
-        buffer[0] = (crc16 & 0x00FF);
-        buffer[1] = ((crc16 & 0xFF00) >> 8);
+        buffer_crc[0] = (crc16 & 0x00FF);
+        buffer_crc[1] = ((crc16 & 0xFF00) >> 8);
+    }
+    /* on a slower processor, we don't want to calculate
+       the CRC after we send the header because there
+       will be a gap */
+    rs485_turnaround_delay();
+    rs485_rts_enable(true);
+    rs485_bytes_send(buffer, 8);
+    if (data_len) {
         rs485_bytes_send(data, data_len);
-        rs485_bytes_send(buffer, 2);
+        rs485_bytes_send(buffer_crc, 2);
     }
     rs485_rts_enable(false);
 }
@@ -1211,11 +1216,15 @@ uint16_t dlmstp_receive(
         InputBuffer = pdu;
         InputBufferSize = max_pdu;
     }
-    /* only do receive state machine while we don't have a frame */
-    if ((MSTP_Flag.ReceivedValidFrame == false) &&
+    while ((MSTP_Flag.ReceivedValidFrame == false) &&
         (MSTP_Flag.ReceivedValidFrameNotForUs == false) &&
         (MSTP_Flag.ReceivedInvalidFrame == false)) {
+        /* only do receive state machine while we don't have a frame */
         MSTP_Receive_Frame_FSM();
+        /* process another byte, if available */
+        if (!rs485_byte_available(NULL)) {
+            break;
+        }
     }
     if (MSTP_Flag.ReceivedValidFrameNotForUs) {
         MSTP_Flag.ReceivedValidFrameNotForUs = false;
@@ -1246,11 +1255,6 @@ void dlmstp_set_mac_address(
     /* Master Nodes can only have address 0-127 */
     if (mac_address <= 127) {
         This_Station = mac_address;
-        /* FIXME: implement your data storage */
-        /* I2C_Write_Byte(
-           EEPROM_DEVICE_ADDRESS,
-           mac_address,
-           EEPROM_MSTP_MAC_ADDR); */
         if (mac_address > Nmax_master)
             dlmstp_set_max_master(127);
     }
diff --git a/bacnet-stack/ports/bdk-atxx4-mstp/rs485.c b/bacnet-stack/ports/bdk-atxx4-mstp/rs485.c
index d1c68b97..34a67d2c 100644
--- a/bacnet-stack/ports/bdk-atxx4-mstp/rs485.c
+++ b/bacnet-stack/ports/bdk-atxx4-mstp/rs485.c
@@ -53,18 +53,33 @@ static FIFO_BUFFER Receive_Buffer;
 
 static struct etimer Silence_Timer;
 
+/****************************************************************************
+* DESCRIPTION: Determines the amount of silence time elapsed
+* RETURN:      true if the amount of silence time has elapsed
+* NOTES:       none
+*****************************************************************************/
 bool rs485_silence_time_elapsed(
     uint16_t milliseconds)
 {
     return timer_elapsed_milliseconds_short(&Silence_Timer, milliseconds);
 }
 
+/****************************************************************************
+* DESCRIPTION: Resets the silence timer
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 void rs485_silence_time_reset(
     void)
 {
     timer_elapsed_start(&Silence_Timer);
 }
 
+/****************************************************************************
+* DESCRIPTION: Configures the RTS output
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 static void rs485_rts_init(
     void)
 {
@@ -72,7 +87,11 @@ static void rs485_rts_init(
     BIT_SET(DDRD, DDD4);
 }
 
-/* enable the transmit-enable line on the RS-485 transceiver */
+/****************************************************************************
+* DESCRIPTION: enable the transmit-enable line on the RS-485 transceiver
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 void rs485_rts_enable(
     bool enable)
 {
@@ -83,12 +102,22 @@ void rs485_rts_enable(
     }
 }
 
+/****************************************************************************
+* DESCRIPTION: enable the UART receiver and interrupt
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 static void rs485_receiver_enable(
     void)
 {
     UCSR0B = _BV(TXEN0) | _BV(RXEN0) | _BV(RXCIE0);
 }
 
+/****************************************************************************
+* DESCRIPTION: delay for 40 bit times
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 void rs485_turnaround_delay(
     void)
 {
@@ -114,6 +143,11 @@ void rs485_turnaround_delay(
     BIT_SET(UCSR0A, TXC0);
 }
 
+/****************************************************************************
+* DESCRIPTION: Interrupt service routine for UART Receiver
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 ISR(USART0_RX_vect)
 {
     uint8_t data_byte;
@@ -128,6 +162,11 @@ ISR(USART0_RX_vect)
     }
 }
 
+/****************************************************************************
+* DESCRIPTION: Checks for data on the receive UART, and handles errors
+* RETURN:      none
+* NOTES:       none
+*****************************************************************************/
 bool rs485_byte_available(
     uint8_t * data_register)
 {
@@ -135,19 +174,31 @@ bool rs485_byte_available(
 
     if (!FIFO_Empty(&Receive_Buffer)) {
         led_on_interval(LED_4, 1);
-        *data_register = FIFO_Get(&Receive_Buffer);
+        if (data_register) {
+            *data_register = FIFO_Get(&Receive_Buffer);
+        }
         data_available = true;
     }
 
     return data_available;
 }
 
+/****************************************************************************
+* DESCRIPTION: returns an error indication if errors are enabled
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 bool rs485_receive_error(
     void)
 {
     return false;
 }
 
+/****************************************************************************
+* DESCRIPTION: Transmits a frame using the UART
+* RETURN:      none
+* NOTES:       none
+*****************************************************************************/
 void rs485_bytes_send(
     uint8_t * buffer,   /* data to send */
     uint16_t nbytes)
@@ -181,12 +232,22 @@ void rs485_bytes_send(
     return;
 }
 
+/****************************************************************************
+* DESCRIPTION: Returns the baud rate that we are currently running at
+* RETURN:      baud rate in bps
+* NOTES:       none
+*****************************************************************************/
 uint32_t rs485_baud_rate(
     void)
 {
     return Baud_Rate;
 }
 
+/****************************************************************************
+* DESCRIPTION: configure the UART baud rate
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 static void rs485_baud_rate_configure(
     void)
 {
@@ -196,6 +257,11 @@ static void rs485_baud_rate_configure(
     UBRR0 = (F_CPU / (8UL * Baud_Rate)) - 1;
 }
 
+/****************************************************************************
+* DESCRIPTION: set the UART baud rate to a standard value
+* RETURN:      true if the baud rate is valid
+* NOTES:       none
+*****************************************************************************/
 bool rs485_baud_rate_set(
     uint32_t baud)
 {
@@ -223,6 +289,11 @@ bool rs485_baud_rate_set(
     return valid;
 }
 
+/****************************************************************************
+* DESCRIPTION: initialize the hardware UART
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 static void rs485_usart_init(
     void)
 {
@@ -243,6 +314,11 @@ static void rs485_usart_init(
     BIT_CLEAR(PRR, PRUSART0);
 }
 
+/****************************************************************************
+* DESCRIPTION: read any non-volatile data
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 static void rs485_init_nvdata(
     void)
 {
@@ -278,6 +354,11 @@ static void rs485_init_nvdata(
     rs485_baud_rate_configure();
 }
 
+/****************************************************************************
+* DESCRIPTION: initialize the module
+* RETURN:      nothing
+* NOTES:       none
+*****************************************************************************/
 void rs485_init(
     void)
 {