When running Win2016 guests under bhyve, data transfers over serial ports from the guest to the host would stall. The investigation recorded in [[ https://smartos.org/bugview/OS-7215 | OS-7215 ]] found that the UART emulation was not properly asserting an interrupt when certain register values were manipulated from the guest. This would cause the outgoing to transmission to stall while the guest waited for a TX interrupt that would never arrive.