Magic Trackpad on MBP and Mac Mini with KVM

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I just got myself the 4 computer, single monitor KVM from the store (the 14-display-port-kvm-single-4computer) and it works great with my Keychron K8 (not the full QMK-compatible K8 Pro - mistakes were made) connected wired via USB to the first HID port on the KVM and a Logitech MX Master 2S connected through its dongle to the second HID port. I’m sharing these peripherals with a 2020 13" MacBook Pro (Intel), a 2023 Mac Mini M2 Pro, and a little AMD-based NUC that runs Proxmox. So far, so good.

Now I tried connecting my Magic Trackpad instead of the MX Master, and this is where the trouble starts! If I connect the USB Lightning cable to the second HID port on the KVM, I can switch between the MBP and the Mini, but the Mini hangs after about 15 seconds or so. First the trackpad quits working (it works for about the first 5 seconds after the switch), and then eventually the entire Mac Mini hangs and finally reboots after about a minute or so.

I also tried connecting the trackpad to the regular USB port, with much the same results.

I assume (but don’t know 100% for sure) that the Magic Trackpad actually connects via Bluetooth, even when I use the cable, which I guess is where the problem comes from. My hypothesis is that while the USB connection switches, it’s not the full extent of the trackpad’s connectivity, so then it tries to drag the Bluetooth connection after it and something in that process seems to be going horribly sideways.

Does anybody have any experience with this and maybe some suggestions how I can get this to work properly? I’d love to be able to use the Trackpad, since I’ve come to really rely on its gesture support for the MacOS devices…

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Have you tried unpairing the bluetooth and only connecting through USB? Worth a shot if your hypothesis is correct.

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Yes, I did. Unfortunately as soon as I connect the USB, it just pairs over BT again. That’s why I said I suspect that the USB is only a partial connection and it actually uses BT for most of its communication. If you search for “Connect an Apple wireless accessory with Mac” you can find Apple’s article that says “To use your Apple wireless keyboard, mouse, or trackpad, you first need to connect the device with your Mac to enable Bluetooth.” (sorry, I’d post the link here, but I’m not allowed to include that). So even after I unpaired it, as soon as I connected it via USB, it connected itself via BT again. AFAIK there is no way to prevent that - but I’m more than willing to admit I could be wrong about that and that there is some magic incantation that will allow the trackpad to use USB only. I just don’t know what that would be. ;]

However, based on your suggestion I tried one more thing: turning off BT on both my MBP and Mini. Interesting result there was that it actually worked for a little bit, just like before! So my theory that it HAS to use BT is actually wrong, it DOES work over USB-only! However it still locks up on my Mini after I do a switch. :confused: (Where “locks up” means the trackpad stops working about 5-15s after I switch to the Mini and then if I leave the USB connected, eventually it ends up crashing the Mini entirely.)

So my new hypothesis is that it’s something in the Mini’s USB stack that’s causing the problem. I just have no idea how to debug that or what to do about it. :sob:

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Try rebooting the kvm and only use the usb3 port. Usb3 port is straight passthrough no fixups

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Huh, whaddaya know - the front USB3 port seems to work fine - awesome! Thanks Wendell! ;]

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