These functions are provided for the user application attached backend
handler routines. They are used to provide responses back to the remote
client, with the necessary control thread and transport layer
information referenced by the
cyg_handle_t ctx parameter passed to
the backend handler function.
For handlers that can provide immediate responses the functions can be called directly from the handler function (in the main MODBUS control thread context). If the handler cannot provide an immediate response, then the processing should be deferred to another thread which can then subsequently use the same API to deliver a response.
Note: For valid responses it is the responsibility of the handler function to return a correctly formatted PDU object to the client.