API SM_NONE (integer value 0)

Questions SimpleMotion
1

Hi Everyone,

I’m trying to use Python to create a wrapper that will interact with a Granite servo motor using the SimpleMotion V2 API. However, I when I try to open the bus using “smbus smOpenBus( const char * devicename )” I get a return of “0”. Which according to the documentation is never returned.

SM_NONE (integer value 0)

Never returned

Now I know it accesses the COM port because once I run the command, the COM port is locked to all other devices. But the return code baffles me.

Any help or insight would be appreciated.

2

I guess the devicename is something that could go wrong… and it is also platform dependant.

3

Thanks for the reply Mika. What do you mean the device name could go wrong? The device name according to the documentation is just the COM port.

    #Import Ctypes library for calling C type functions
    from ctypes import *
    import time

    #Load of smv2 dll library
    smv2 = cdll.LoadLibrary(r"C:\Users\me\Granite Source     Files\SMV2VScppExample\VScppExample\Debug\smv2.dll")

    #Com port pointer set
    comPort = c_char_p('COM12'.encode('utf-8'))

    #Call command
    busHandle = smv2.smOpenBus(comPort)

    #Print SM Status
    print(busHandle)
4

Documentation is at simplemotion.h header.

-devicename: formatted string that depend on device type to attempt opening. Supported formats/drivers:
--Serial port device:
---on Windows: COMn where n=port number, i.e. COM2
---on Linux: /dev/ttyN where N=port name, i.e. /dev/ttyUSB0 or /dev/ttyS0
---on macOS: /dev/tty.cuN where N=port name

… but you are on Windows, so COM12 should work. I wonder what is then causing it to return 0…

5

the smOpenBus shoudl return an index (from 0 to SM_MAX_BUSES) and a 0 is a valid handle, if I understand the code correctly.

6

Ok. I see what you’re looking at. However the documentation wiki says it should never be returned. It also doesn’t say what 0 would mean even if it is a valid handle :fearful:

I’ve also now tried the same code and USB dongle on a different machine. I know it’s not the dongle because the Granity software can connect with it.

So it seems to be something with the API.

7

Well the smOpenBus does not return a SM_STATUS but a handle. -1 would be an error handle.

8

OK! So I’ve gotten it to work. It turns out you are right Mika. 0 is a valid handle. I recompiled a different library from the git and it worked.

I think the documentation needs updating to say that 0 is valid, not “Never Returned”