I have a Windows Server 2003 VM running on ESXi6.5.0.
I have a Comtrol RocketPort Express PCIe card installed on the host machine and have configured this for 'passthrough' to my VM. This card provides 32 physical serial communication ports. Within my VM I am using Calta Modbus simulator to run comms loop tests. I have he following connected up:
Com3 -> Com19
Com4 -> Com20
Com5 -> Com21
Com6 -> Com22
Com10 -> Com26
The Modbus communications are poor. Many messages are failing. See attached file (ESXi Comms Test Overnight.PNG).
In addition, I have noticed that if insert a USB memory stick into the host machine (I have this mapped to the VM) that the entire Windows process stalls for a few seconds. This is evident from the windows clock being frozen. Of course this only happens while I am running my loop tests. Without the Modbus comms running, inserting a USB stick is fine.
I have tried using Microsoft Process Explorer to determine what could be causing the problem and this seems to point to 'Interrupts', more specifically 'Hardware Interrupts and DPCs'. See attached 'Process Explorer - Interrups.PNG'.
It may be that this problem is a show stopper for our intended purpose. Would there be any reason for 'passthrough' to struggle in the above situation?