id summary reporter owner description type status component version resolution keywords cc guest host 17116 Serial device data not transmitted to Win XP guest => fixed in SVN/next maintenance ruga "VirtualBox V5.1.14 Host: Win 7 Ultimate Guest: Win XP Pro We attach a power supply unit (PSU) to serial port COM1 of the physical machine running Win 7. The PSU sends status data to COM1 permanently. In the guest (WinXP) the virtual serial port COM1 is mapped to the real serial port COM1. This is the serial port configuration in the guest: ""Enable Serial Port"": Checked ""Port Number"": COM1 IRQ: 4 I/O Port: 0x3F8 ""Port Mode"": Host Device ""Connect to existing pipe/socket"": Checked ""Path/Address"": COM1 In the guest an application should monitor the state of the PSU. Now the Problem: When we start the VM the application doesn't receive the status data initially. :( Only if we send any character from the VM to COM1, the status data is received by the monitor application as expected. Further we can see, if we don't send a character to COM1, close the VM and start it again, the PSU status data is received at once. This succeeds as long as we don't reboot the host. After rebooting the host the next time and starting the VM receiving the PSU status data fails again. It seems, that VirtualBox requires sending some data to the serial port first, before it is able to receive data from the serial port. By the way, running the monitoring application in the host works perfectly. We have deeper analyzed the problem by watching the IOCTL traffic. The results are described in detail in the forum thread https://forums.virtualbox.org/viewtopic.php?f=2&t=84667&sid=a6eb50e33e626459cd4dbf1a3748cc5f&p=402188#p402188 There you will also find screenshots showing the critical IOCTL sequences. Many thanks ! " defect closed uart VirtualBox 5.1.14 fixed serial port, COM, data transmission Windows Windows