I want to compare RS232 traffic between two scenarios. Feel free to skip the background and jump right to the traffic logs. Can anyone explain to me why I may be seeing differences in these scenarios?
History
I have been trying to debug some RS232 communication issues between a very legacy hardware device and an application running on a Win98 PC. The comms between this PC and the device work perfectly, but I have not been able to get success with any other setups (virtualization, USB Com Port Adapter).
I'll cut out as much of the history as possible. I have an application running on a Win98SE Virtual PC (Microsoft) and on physical hardware running Win98SE.
On the Virtual PC side I am forwarding COM2 traffic to a physical COM port, which happens to be a USB COM Port Adapter.
After disabling FIFO buffers, the port appears to work without a hitch. I can transfer files between the real Win98SE PC and the Virtual Machine over the com port using HyperTerminal.
I did some PortMon analysis, and I found that the application repeatedly sends a particular set of bytes, sending this sequence of bytes to the hardware, I get varying amounts of data sent back to me.
However, when I run the application on the Virtual PC, I note that the application does not communicate with the hardware, it reports communication errors, data does not update, etc.
Traffic Logs
Running PortMon on the real PC, I get this sequence of typical communication (this works):
19 2:17:20 PM COMAPP VCOMM_WriteComm COM2 SUCCESS Length: 4: 81 02 00 7E
20 2:17:20 PM COMAPP EventNotifyProc COM2 VOID : TXEMPTY
21 2:17:20 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS EVENT
22 2:17:20 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
23 2:17:20 PM COMAPP EventNotifyProc COM2 VOID : RXCHAR
24 2:17:20 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS RECEIVE
25 2:17:20 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
26 2:17:20 PM COMAPP VCOMM_ReadComm COM2 SUCCESS Length: 1: 06
27 2:17:20 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS NONE
28 2:17:20 PM COMAPP VCOMM_WriteComm COM2 SUCCESS Length: 4: 80 02 00 7F
29 2:17:20 PM COMAPP EventNotifyProc COM2 VOID : TXEMPTY
30 2:17:20 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS EVENT
31 2:17:20 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
32 2:17:20 PM COMAPP EventNotifyProc COM2 VOID : RXCHAR
33 2:17:20 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS RECEIVE
34 2:17:20 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
35 2:17:20 PM COMAPP VCOMM_ReadComm COM2 SUCCESS Length: 1: 06
36 2:17:20 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS NONE
Running PortMon on the Virtual PC, I get this sequence of communications (this doesn't work):
21 4:56:30 PM COMAPP VCOMM_WriteComm COM2 SUCCESS Length: 4: 81 02 00 7E
22 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
23 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
24 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
25 4:56:30 PM COMAPP EventNotifyProc COM2 VOID : TXEMPTY
26 4:56:30 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS EVENT
27 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
28 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
29 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
30 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
31 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
32 4:56:30 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
33 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
34 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
35 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
36 4:56:32 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS NONE
37 4:56:32 PM COMAPP VCOMM_WriteComm COM2 SUCCESS Length: 4: 80 02 00 7F
38 4:56:32 PM COMAPP EventNotifyProc COM2 VOID : TXEMPTY
39 4:56:32 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS EVENT
40 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
41 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
42 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
43 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
44 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
46 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
47 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
48 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
49 4:56:32 PM COMAPP VCOMM_ClearCommError COM2 SUCCESS NOERROR
50 4:56:32 PM COMAPP VCOMM_GetCommEventMask COM2 SUCCESS NONE
There are some obvious differences:
- The virtualized app excessively clears Comm Errors, when they don't appear to exist.
- The virtualized app never receives RXCHAR, and thus never reads the 06.
I am very new to this kind of analysis, but what immediately comes to mind is that some of the signals (CTS, RTS, DSR, DTR, etc...) may not work with a USB COM Adapter, and perhaps the app requires these signals. Again, I'm no expert, maybe these signals are always required.
If I use IONinja to connect to the hardware, and send the same bytes I am capturing above, I do get the 06 response (among other responses), but the application does not recognize this.
I found this question, but it doesn't quite answer my question:
Disadvantages of USB to RS232 dongles