add comment about problems with PCI-E x1 slots

Author: floe

README.md

@@ -51,11 +51,17 @@ Finally, it's also possible that your executable is not actually using the patch
 
 ### I'm seeing the color camera stream, but no depth/IR (black windows).
 
-The depth packet processor runs on OpenGL by default. You can try alternatives, such as OpenCL (by running `Protonect cl`) or CPU (`Protonect cpu`). At least the CPU DPP should always produce some output, although slow. For OpenCL on Intel/Linux, you can also try to set `/sys/module/i915/parameters/enable_cmd_parser` to 0.
+The depth packet processor runs on OpenGL by default. You can try alternatives, such as OpenCL (by running `Protonect cl`) or CPU (`Protonect cpu`). At least the CPU DPP should always produce some output, although slow.
+
+For OpenCL on Intel/Linux, you can also try to set `/sys/module/i915/parameters/enable_cmd_parser` to 0.
 
 ### Can I use multiple Kinect v2 devices on one machine?
 
-Yes - in fact, this has been reported to work for up to 5 devices on a high-end PC using multiple separate PCI Express USB3 expansion cards (with NEC controller chip). If you're using Linux, you may have to increase USBFS memory buffers by appending `usbcore.usbfs_memory_mb=64` to your kernel commandline. Depending on the number of Kinects, you may need to use an even larger buffer size.
+Yes - in fact, this has been reported to work for up to 5 devices on a high-end PC using multiple separate PCI Express USB3 expansion cards (with NEC controller chip). 
+
+If you're using Linux, you may have to increase USBFS memory buffers by appending `usbcore.usbfs_memory_mb=64` to your kernel commandline. Depending on the number of Kinects, you may need to use an even larger buffer size.
+
+If you're using an expansion card, make sure it's not plugged into an PCI-E x1 slot. A single lane doesn't have enough bandwidth. x8 or x16 slots usually work.
 
 ## Maintainers: