Feature/mstp extended frames (#529)

* added MSTP extended frames to bacnet/datalink/mstp.c module. Thank you, Simon!

* auto-size some FIFO buffers for MSTP

* add COBS library to MSTP builds

---------

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

ports/stm32f4xx/Makefile

@@ -137,7 +137,7 @@ OPTIMIZE_FLAGS += -DNDEBUG
 
 BACNET_FLAGS = -DBACDL_MSTP=1
 BACNET_FLAGS += -DBACAPP_ALL
-BACNET_FLAGS += -DMAX_APDU=480
+BACNET_FLAGS += -DMAX_APDU=1476
 BACNET_FLAGS += -DBIG_ENDIAN=0
 BACNET_FLAGS += -DMAX_TSM_TRANSACTIONS=0
 BACNET_FLAGS += -DMAX_CHARACTER_STRING_BYTES=64

ports/stm32f4xx/bacnet.ewp

@@ -224,7 +224,7 @@
                     <state>USE_STDPERIPH_DRIVER</state>
                     <state>STM32F4XX</state>
                     <state>BACDL_MSTP</state>
-                    <state>MAX_APDU=480</state>
+                    <state>MAX_APDU=1476</state>
                     <state>BIG_ENDIAN=0</state>
                     <state>MAX_TSM_TRANSACTIONS=1</state>
                 </option>

ports/stm32f4xx/rs485.c

@@ -33,17 +33,18 @@
 #include "bacnet/basic/sys/mstimer.h"
 #include "bacnet/bits.h"
 #include "bacnet/basic/sys/fifo.h"
+#include "bacnet/datalink/dlmstp.h"
 #include "bacnet/datalink/mstpdef.h"
 #include "rs485.h"
 
 /* buffer for storing received bytes - size must be power of two */
-/* BACnet DLMSTP_MPDU_MAX for MS/TP is 501 bytes */
-static uint8_t Receive_Queue_Data[512];
+/* BACnet DLMSTP_MPDU_MAX for MS/TP is 1501 bytes */
+static uint8_t Receive_Queue_Data[NEXT_POWER_OF_2(DLMSTP_MPDU_MAX)];
 static FIFO_BUFFER Receive_Queue;
 
 /* buffer for storing bytes to transmit */
-/* BACnet DLMSTP_MPDU_MAX for MS/TP is 501 bytes */
-static uint8_t Transmit_Queue_Data[512];
+/* BACnet DLMSTP_MPDU_MAX for MS/TP is 1501 bytes */
+static uint8_t Transmit_Queue_Data[NEXT_POWER_OF_2(DLMSTP_MPDU_MAX)];
 static FIFO_BUFFER Transmit_Queue;
 
 /* baud rate of the UART interface */