Glad to hear from you.
Yeah I see you point. Comparing with Wi-Fi running at 5800MHz the 480Mbps on USB2.0 is really not that fast.
However I am I'm high school NCEA Level 2 if it starts to explain a little why is it really hard on my behalf - I don't have the basic knowledge to cut it.
Ok so there are a few points you made if I get it right:
Route them close to each other, and make sure that their length match up as much as possible;
Control the distance between track, from track to ground, and from track to back of the board, which is fixed 1.6mm norm isnt it?
And not to route anything below USB line, so it shall be plain ground with nothing on it.
So I have a few questions:
1. Does it matter to have a DC line(like VCC) instead of GND under the data line?
2. Does it matter to not have copper pour under the data line or do I have to have copper pour?
3. Do I need to add caps to the D+ and D-?
4. I see that on datasheet of RPi-CM3, USB is required to be 90 ohm differential PCB traces. However, nothing has been stated on DSI(Display Serial Interface) and CSI(Camera Serial Interface). On the other hand, on the schematic of the official CMIO v1.1, DSI and CSI are declared to be
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matched length 100R differential pairs
which got me confused: When datasheet doesn't say anything but reference design does, do I need need to take that into account? Plus, on behalf of DSI and CSI itself, should I use matched length track with controlled impedance or do I not need to care at all? Especially the I^2C port inside DSI and CSI is also declared as matched length track with controlled impedance, which I have seen no where else. By contrast, interestingly, the SD seems to not have any requirement relates to length matching and impedance control at all.