Moving from MSTP.c

Before the removal of MSTP.c and MSTP.h (the stack’s C MS/TP engine), your application compiled source/MSTP.c, called MSTP_Init() and MSTP_Loop(), and bridged the engine to the stack with the per-port message callbacks. That is a breaking change for anything that compiled MSTP.c itself, such as the BACnetServerMSTPExampleCPP example or an application of yours. The Zephyr adapter in adapters/zephyr already uses the interface below. The engine now lives in the stack (source/BACnetMSTPEngine.cpp), one per port, and the same behaviour is behind a byte-level interface.

`MSTP.c`	The stack now
`MSTP_Init()` with the callbacks and the station	Register `BACnetStack_RegisterCallbackMSTPReceiveBytes()`, `...MSTPSendBytes()` and `...MSTPMicroseconds()` once, before or after you add the Network Port object. There is no init call. The engine starts on the first `BACnetStack_Tick()` after the port exists.
`MSTP_SetBaudRate()`, `MSTP_SetMaxMaster()`, `mstp_settings.Nmax_info_frames`, the station in `MSTP_Init()`	The Network Port object’s Link_Speed, Max_Master, Max_Info_Frames and MAC_Address, served by your property callbacks. There are no setters.
`mstp_RecvByte` (one octet)	`CallbackMSTPReceiveBytes`: copy every octet that is waiting, up to the size of the buffer, and return the count.
`mstp_SendByte`	`CallbackMSTPSendBytes`: the same body. Return only after the last stop bit has left the transmitter.
`mstp_Sleep`, `mstp_TimerReset`, `mstp_TimerDifference`	Delete all three. `CallbackMSTPMicroseconds` returns one monotonic microsecond clock that wraps at 2^32. The engine never sleeps.
`mstp_RS485EnableTXDPin` and `MSTP_SetRS485EnableTXDPin()`	`BACnetStack_RegisterCallbackMSTPTransmitEnable()`, with the port instance as a first parameter.
`mstp_FrameHeaderCallBack`	`BACnetStack_RegisterCallbackMSTPFrameHeader()`, or the counters.
`mstp_EventLog`, `MSTP_DEBUG`, `MSTP_DEBUG_SPRINTF`	Gone.
`mstp_APDUCallBack` and your receive-message queue; `MSTP_InsertFrameToSend()` and your send-message callback	Delete the queues and both callbacks. The stack queues outgoing NPDUs for the engine and takes received NPDUs from it, inside `BACnetStack_Tick()`.
`MSTP_Loop()`	`BACnetStack_LoopMSTP(networkPortInstance)`. It may run on its own thread, with no lock shared with `BACnetStack_Tick()`. Start that thread after the Network Port object is added (the stack forbids adding or removing Network Port objects while another thread is inside the call); the Zephyr adapter’s `cbz::mstp::Start()` does so.
`MSTP_IsConnected()`	The `BACnetMSTPCounter_InTokenRing` entry of `BACnetStack_GetMSTPCounters()`.
`MSTP_ReportReceiveError()`	`BACnetStack_ReportMSTPReceiveError(networkPortInstance)`.

The sizes that MSTP.h defined as macros are constants of the engine class, in source/BACnetMSTPEngine.h:

Was (`MSTP.h`)	Is	Value
`MSTP_MAX_PACKET_OCTETS`	`CASBACnetStack::BACnetMSTPEngine::MAX_PACKET_OCTETS`	501
`MSTP_MAX_NPDU_OCTETS`	`CASBACnetStack::BACnetMSTPEngine::MAX_NPDU_OCTETS`	1497
`MSTP_INPUT_BUFFER_SIZE`	`CASBACnetStack::BACnetMSTPEngine::INPUT_BUFFER_SIZE`	1508

They are plain enumerators, usable in array sizes, and exist when STACK_OPTION_DATA_LINK_LAYER_MSTP is on. The old -DMSTP_MAX_NPDU_OCTETS=501 option for saving memory has no equivalent: the engine’s buffers are a fixed size.

If you would rather keep your own engine, stay in packet mode: register no byte callbacks and keep the message callbacks as they were. Nothing else in the stack depended on MSTP.c.