That should work - it does on a P4317. Are you sure the 2nd command syntax is correct? You give the 1st working command, but not the second non-working one.

Nice to hear it should work, I have new hope now. The second command is: ddm.exe" /1:SetActiveInput DP /Exit

I know this command is right because I can execute it on the Windows machine and I can see the display switching (to the same input it was before, DP).

The command is being executed on the Windows machine from the Apple computer while the monitor has it's input on the Apple computer

DDM does not have an Apple OS version. So how could a command executed from the Windows computer operating system "talk" to the Apple computer operating system?

" from the Apple computer while the monitor has it's input on the Apple computer"

That would imply that the Apple computer had to have DDM installed on it to run/execute the command, which it cannot do because DDM won't install on the Apple OS?

The failure could be due to some limitation of the U2717D, but have a look at the DDM diagnostic log to see if anything is recorded there. While holding down the SHIFT key, right-click on the DDM system tray icon and select "Save diagnostic report" from the popup menu; then scroll thru the file you saved to find the command.

Obviously, you will need to omit the "/exit" parameter from your command-lines or you won't be able to save the log.

Ok I have done that. I says

"Skipping unsupported device MONITOR\Default_Monitor\{4d36e96e-e325-11ce-bfc1-08002be10318}\0002"

Start of log:

===============================================================

Diagnostic Report, generated 8-11-2017 (10.0.14393)

Copyright (c) 1995-2017, EnTech Taiwan.

Version = 1.31.0.1897

OS = 10.0.14393.2 x64

Mechanism = 3

Account = Standard

Command line = "c:\util\dell display manager\ddm.exe" /1:SetActiveInput DP

////////////////////////////////////////

GridType = 0x00000000

GridType.DEL40EA.J0XYN68F341S = 0x00000000

GridType.DEL40EA.J0XYN68F341S{562FEC6F-63A1-4267-97B5-B370E2E3FED4} = 0x00000000

LastCheck = 0x0000A823

HintShown = 0x00000001

AutoRestoreWindowLayout = 0x00000000

AppScan.DEL40EA.J0XYN68F341S = 0x00000004

DEL40EA = 0x00000001

FW.DEL40EA.J0XYN68F341S = 0x00004103

EnumErrorCount = 0x00000000

Metro.DEL40EA.J0XYN68F341S = 0x00000001

D3D.DEL40EA.J0XYN68F341S = 0x00000004

DEL40EA.J0XYN68F341S\c:\util\dell display manager\ddm.exe = 0x00000000

DEL40EA.J0XYN68F341S\C:\Util\Dell Display Manager\ddm.d3d = 0x00000004

DEL40EA.J0XYN68F341S\C:\Kantoor\Mozilla Thunderbird\thunderbird.exe = 0x00000000

DEL40EA.J0XYN68F341S\C:\Kantoor\Microsoft Office\Office16\WINWORD.EXE = 0x00000000

DEL40EA.J0XYN68F341S\C:\Kantoor\Microsoft Office\Office16\POWERPNT.EXE = 0x00000001

DEL40EA.J0XYN68F341S\C:\Multimedia\Adobe Photoshop CC 2015\Photoshop.exe = 0x00000001

DEL40EA.J0XYN68F341S\C:\Kantoor\Microsoft Office\Office16\EXCEL.EXE = 0x00000000

DEL40EA.J0XYN68F341S\C:\Program Files\Windows NT\Accessories\WORDPAD.EXE = 0x00000000

DEL40EA.J0XYN68F341S\C:\WINDOWS\system32\mspaint.exe = 0x00000001

DEL40EA.J0XYN68F341S\C:\Program Files (x86)\Windows Media Player\wmplayer.exe = 0x00000002

DEL40EA.J0XYN68F341S\C:\Program Files\Internet Explorer\IEXPLORE.EXE = 0x00000001

DEL40EA.J0XYN68F341S\C:\WINDOWS\SysNative\ApplicationFrameHost.exe*Microsoft Edge = 0x00000001

DEL40EA.J0XYN68F341S\C:\WINDOWS\SysNative\ApplicationFrameHost.exe = 0x00000001

////////////////////////////////////////

07:17:12.205...Log opened

07:17:12.691...LanguageID = 00000409 00000409 00000413

07:17:12.699...Build = 1.31.0.1897

07:17:12.699...Windows handles = 0001011A 000100C0 00010120

07:17:12.700...OS monitor sleep timeout value = 900 ms.

07:17:12.701...Applied DPI = 96-96

07:17:12.701...VM = 0

07:17:12.872...Starting enumeration

07:17:12.884......Skipping unsupported device MONITOR\Default_Monitor\{4d36e96e-e325-11ce-bfc1-08002be10318}\0002

07:17:12.887...Ending enumeration

07:17:12.888...New=Default_Monitor.0002

07:17:13.000...Video power down timeout = 900

07:17:13.001...Display powered ON

07:17:13.002...User session connect

07:17:20.498...Refreshing screen object

07:17:27.949...Old=Default_Monitor.0002

07:17:27.961...New=DEL40EA.0001

07:17:27.971...HPD event detected... pausing

07:17:34.489...Changed display configuration

07:17:34.494...Starting enumeration

07:17:34.551...1. DEL40EA.J0XYN68F341S on Intel(R) HD Graphics 530

07:17:34.552......Monitor assignment = 1

07:17:34.552......Adapter name = \\.\DISPLAY1

07:17:34.553......Monitor name = Dell U2717D (DP)

07:17:34.553......Vendor ID = 8086

07:17:34.555......GPU driver = igdumdim64 21.20.16.4534

07:17:34.555......Flags = 00000005.00000003

07:17:34.556......Display tag = 9C56A5EA

07:17:34.556......Monitor number = 1

07:17:34.557......Monitor handle = 00010001

07:17:34.562......Raw EDID = 00FFFFFFFFFFFF0010ACEA4053313433211A0104A53C22783AEE95A3544C99260F5054A54B00714FA9408180D1C00101010101010101565E00A0A0A029503020350055502100001A000000FF004A3058594E363846333431530A000000FC0044454C4C205532373137440A20000000FD00324B1E5819010A202020202020019C

07:17:34.619......VCP10 = 0064004B

07:17:34.620......OS device handle = 00010001.00000000

07:17:34.620......Capabilities string = (prot(monitor)type(lcd)model(u2717d)cmds(01 02 03 07 0c e3 f3)vcp(02 04 05 08 10 12 14(01 04 05 06 08 09 0b 0c)16 18 1a 60(10 0f 11) aa(01 02 03 04) ac ae b6 c6 c8 c9 d6(01 04 05) dc(00 02 03 05) df e0 e1 e2(00 01 02 04 0b 0c 0d 0f 10 11 13 14 19) f0(08) f1 f2 fd)mccs_ver(2.1)mswhql(1)) (cached)

07:17:34.837......Configuration = FFFF0003.FFFF0074.1A21

07:17:34.838......Model = Dell U2717D

07:17:34.838......Model year = FY17

07:17:34.839......Capabilities = (prot(monitor)type(lcd)model(u2717d)cmds(01 02 03 07 0c e3 f3)vcp(02 04 05 08 10 12 14(01 04 05 06 08 09 0b 0c)16 18 1a 60(10 0f 11) aa(01 02 03 04) ac ae b6 c6 c8 c9 d6(01 04 05) dc(00 02 03 05) df e0 e1 e2(00 01 02 04 0b 0c 0d 0f 10 11 13 14 19) f0(08) f1 f2 fd)mccs_ver(2.1)mswhql(1)) (cached)

07:17:34.843......Opcodes supported = 02,04,05,08,10,12,14,16,18,1A,60,AA,AC,AE,B6,C6,C8,C9,D6,DC,DF,E0,E1,E2,F0,F1,F2,FD

07:17:34.949......Timing = Invalid data (3,47 kHz (+), 60,00 Hz (+))

07:17:34.950...Ending enumeration

07:17:34.963...Creating VCP table on DEL40EA.J0XYN68F341S

07:17:35.018......Opcode 0x12 = 0064004B

07:17:35.122......Opcode 0x60 = 0011000F

07:17:35.232......Opcode 0xAA = FFFF0001

07:17:35.338......Opcode 0xC8 = 00005605

07:17:35.445......Opcode 0xE2 = 00190000

07:18:01.780...\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

07:18:01.780...Dump: complete Windows device enumeration

07:18:01.781...1.DeviceName      = \\.\DISPLAY1

07:18:01.783.....DeviceFlags     = 00000005

07:18:01.784.....DeviceString    = Intel(R) HD Graphics 530

07:18:01.785.....DeviceID        = PCI\VEN_8086&DEV_1912&SUBSYS_86941043&REV_06

07:18:01.786.....DeviceKey       = \Registry\Machine\System\CurrentControlSet\Control\Video\{5ABF565F-4BFF-4295-B22D-870C7D538D67}\0000

07:18:01.787.....a.MonitorName   = \\.\DISPLAY1\Monitor0

07:18:01.788.......MonitorFlags  = 00000003

07:18:01.790.......MonitorString = Dell U2717D (DP)

07:18:01.792.......MonitorID     = MONITOR\DEL40EA\{4d36e96e-e325-11ce-bfc1-08002be10318}\0001

07:18:01.792.......MonitorKey    = \Registry\Machine\System\CurrentControlSet\Control\Class\{4d36e96e-e325-11ce-bfc1-08002be10318}\0001

07:18:01.793.......Raw EDID      = 00FFFFFFFFFFFF0010ACEA4053313433211A0104A53C22783AEE95A3544C99260F5054A54B00714FA9408180D1C00101010101010101565E00A0A0A029503020350055502100001A000000FF004A3058594E363846333431530A000000FC0044454C4C205532373137440A20000000FD00324B1E5819010A202020202020019C

07:18:01.794...2.DeviceName      = \\.\DISPLAY2

07:18:01.795.....DeviceFlags     = 00000000

07:18:01.796.....DeviceString    = Intel(R) HD Graphics 530

07:18:01.796.....DeviceID        = PCI\VEN_8086&DEV_1912&SUBSYS_86941043&REV_06

07:18:01.799.....DeviceKey       = \Registry\Machine\System\CurrentControlSet\Control\Video\{5ABF565F-4BFF-4295-B22D-870C7D538D67}\0001

07:18:01.801...3.DeviceName      = \\.\DISPLAY3

07:18:01.801.....DeviceFlags     = 00000000

07:18:01.802.....DeviceString    = Intel(R) HD Graphics 530

07:18:01.803.....DeviceID        = PCI\VEN_8086&DEV_1912&SUBSYS_86941043&REV_06

07:18:01.803.....DeviceKey       = \Registry\Machine\System\CurrentControlSet\Control\Video\{5ABF565F-4BFF-4295-B22D-870C7D538D67}\0002

07:18:01.805...Total number of monitors enumerated = 1

07:18:01.808...\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

07:18:01.809...Dumping VCP table on DEL40EA.J0XYN68F341S

07:18:01.863......Opcode 0x02 = 00FF0001

07:18:01.967......Opcode 0x10 = 0064004B

07:18:02.074......Opcode 0x12 = 0064004B

07:18:02.178......Opcode 0x14 = 000C0000

07:18:02.286......Opcode 0x16 = 00640064

07:18:02.392......Opcode 0x18 = 00640064

07:18:02.501......Opcode 0x1A = 00640061

07:18:02.606......Opcode 0x60 = 0011000F

07:18:02.711......Opcode 0xAA = FFFF0001

07:18:02.814......Opcode 0xAC = 00015B44

07:18:02.919......Opcode 0xAE = 00001770

07:18:03.024......Opcode 0xB6 = FFFF0003

07:18:03.128......Opcode 0xC6 = FFFF45CC

07:18:03.232......Opcode 0xC8 = 00005605

07:18:03.339......Opcode 0xC9 = FFFF4103

07:18:03.442......Opcode 0xD6 = FFFF0001

07:18:03.546......Opcode 0xDC = 00050000

07:18:03.650......Opcode 0xDF = FFFF0201

07:18:03.753......Opcode 0xE2 = 00190000

07:18:03.857......Opcode 0xF0 = FFFF0000

07:18:03.961......Opcode 0xF1 = FFFF0003

07:18:04.066......Opcode 0xF2 = FFFF0000

07:18:04.171......Opcode 0xFD = FFFF0074

07:18:04.223......VCP table dumped

Try this:

1. Start DDM on the Windows PC and leave it running with "ddm.exe" (no parameters)

2. Execute the following command-line from the WinPC: "ddm.exe /setactivecontrol mDP"

(this should switch the input to the Mac)

3. Execute the following command-line from the Mac: "ddm.exe /setactivecontrol DP"

(this should switch input back to the WinPC)

Note above that you will be omitting the /exit parameter and the target monitor number since you only have 1 Dell monitor and don't want or need DDM to perform a hardware discovery each time you want to switch inputs.

setactivecontrol is not in the documentation, are you sure about that?

If you meant SetActiveInput, I have tried already to leave ddp.exe running but that changes nothing.

Ok, I tried swamped suggestion (replacing setactivecontrol with setactiveinput). First starting ddm.exe, then switch to the Apple machine using ddm.exe /setactiveinput mDP, then while the input is on mDP, executing ddm.exe /setactiveinput DP on the Windows machine. The input does NOT get switched to DP. Even worse, when I try to get the logging with shift-right click the ddm is crashing.

I very much like the input from an Dell programmer that knows about ddm inner workings. It seems to me that ddm cannot send it's commands to the monitor when the active input is on a computer that does not support it.