USB issues are caused by the 15-port limit in macOS, missing USB mapping, or incorrect port configuration.
Step 1 — Understand the 15-Port Limit
macOS limits each USB controller to 15 ports. A USB 3.0 port counts as two (one USB 2.0 + one USB 3.0).
Step 2 — Map Your USB Ports
Use USBToolBox or USBMap to identify which physical ports correspond to which internal port numbers.
Step 3 — Create a USB Map Kext
Generate a USBMap.kext with only the ports you need. Remove USBInjectAll.kext once your map is in place.
Step 4 — Verify in System Information
Open System Information > USB and confirm all expected devices appear.
Expected Results
- All needed USB ports recognise devices
- USB 3.0 ports achieve expected transfer speeds
- No kernel panics when plugging/unplugging devices
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Original Question: "Keyboard not connecting to Opencore/BiOS"
I just got an MX Keys and while it connected to both Mac and Windows last night flawlessly, I now cannot access my Windows drive because it only pairs to the operating systems themselves. Same with my mouse. I've tried both connecting the universal receiver into a USB port on the motherboard and connecting it via USB cable... still not registering to Opencore/BiOS. Which is doubly confusing because I was able to use it to access Windows via Opencore last night... What am I missing?
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