Windows: serial devices¶

emupos cannot create serial ports on Windows. A serial device there (a scale, a serial scanner, a printer on a serial connection) opens a COM port that already exists, and your POS opens the other end of the link:

  - id: deli
    type: scale
    profile: toledo8217-15kg
    connections:
      - serial: { port: COM5 }   # emupos opens COM5, the POS opens COM6

serial: { pty: true } is not available on Windows; the configuration is rejected with a pointer to this page. For the same reason emupos run --demo leaves the scale out on Windows.

Getting a pair of COM ports¶

Windows has no built-in virtual serial port pairs. Pick one of these:

com0com is blocked with Secure Boot on¶

The com0com 3.0.0.0 installer has a valid signature, but its kernel driver was signed with a 2016 certificate that Windows no longer accepts with Secure Boot on. It installs without a warning, then:

• Device Manager shows the com0com bus device with Code 52 ("Windows cannot verify the digital signature for the drivers required for this device");
• no COM ports appear under "Ports (COM & LPT)";
• the Code Integrity event log has event 3004 for com0com.sys.

emupos doctor reports this as a com0com device with the problem CM_PROB_UNSIGNED_DRIVER. You can check it yourself in PowerShell:

Get-PnpDevice -PresentOnly | Where-Object FriendlyName -like '*com0com*' | Format-List FriendlyName, Status, ConfigManagerErrorCode
Confirm-SecureBootUEFI

To remove it again, run setupc remove 0 from the com0com folder (C:\Program Files (x86)\com0com) in a terminal opened with "Run as administrator".

Creating a com0com pair (Secure Boot off)¶

In a terminal opened with "Run as administrator", in the com0com folder:

.\setupc.exe install PortName=COM# PortName=COM#
.\setupc.exe change CNCA0 RealPortName=COM5
.\setupc.exe change CNCB0 RealPortName=COM6
.\setupc.exe list

PortName=COM# lets Windows assign the numbers and puts both ports under "Ports (COM & LPT)", where POS software looks for them; the two change lines rename them to free numbers. Give emupos one name and your POS the other. A virtual pair passes bytes whatever baud rate or parity each side sets, while a real device would misread them: see "Serial settings" below.

Then make the pair behave like a real null-modem cable:

.\setupc.exe change CNCA0 EmuOverrun=yes,EmuBR=yes
.\setupc.exe change CNCB0 EmuOverrun=yes,EmuBR=yes

EmuOverrun throws away bytes nobody is reading. Without it, writing while the other end is closed blocks the writer for seconds, so a scan or a printer reply can stall until the POS opens its port again. EmuBR sends bytes at the configured baud rate instead of instantly. The trade-off is that bytes written while the POS was away can still turn up when it reopens the port.

Serial settings¶

emupos opens the port with the device profile's settings (a Toledo 8217 scale: 9600 baud, 7 data bits, even parity, 1 stop bit). On Windows emupos cannot see which settings the POS chose on its end, so there are no framing-mismatch warnings as on macOS. Set the POS to the profile's settings yourself.

Replies on Windows arrive about 15 milliseconds after the request, because emupos waits for a short gap in the incoming bytes before handing them to the device. Real hardware takes longer than that.

When the port does not open¶

emupos doctor checks every configured COM port and the com0com driver, and prints a fix for each problem.