Modbus notes
- https://libmodbus.org/ . . . Ubuntu package is 'libmodbus5' and 'libmodbus-dev'
- 2019-11-08 FRI -
When working with FreeModbus, be sure to pay attention to the versions of protocol available, and likely, we only want to enable one of these. See Modbus/include/mbconfig.h. See also Modbus/include/mb.h for instructions on how to initialize and begin to use an instance of FreeModbus stack in given program. Also mention that eMBPoll() routine may be set up as a task in an RTOS, to realize the periodic polling which is part of the stack's runtime manifestation . . .
Looks like also this function to register callbacks for end-user-device-specific Modbus registers will be important:
eMBErrorCode eMBRegisterCB ( UCHAR ucFunctionCode,
pxMBFunctionHandler pxHandler
)
This function signature part of documentation found at https://www.embedded-solutions.at/en/freemodbus/api-documentation/, which gives Doxygen generated API help in an embedded pane in the browser window on which it is visited.
2019-11-12 Tuesday - trying to figure out how pxMBFunctionHandler is defined . . . from http://www.teamfdi.com/uez/docs/mbproto_8h.html:
Typedefs typedef eMBException(* pxMBFunctionHandler )(UCHAR *pucFrame, USHORT *pusLength)
...from this typedef looks like Modbus routines implemented by the end user/end designer must have parameter lists which match "unsigned char pointer, unsigned integer pointer".
^ further references