Hi @matthias.tx and @walter.tx,
We are having a problem with one of our 8MM carriers where the USB is not working. We have numerous boards where it does work and a couple where it doesn’t. Having a look with the scope I can see that USB_1_DP_N looks perfect, nice fast edges, no ringing. However, USB_1_DP_P goes to 3.3V on power up (after stopping a while at 1.8 V) and then toggles only slowly before giving up. I have also checked all the part placements are correct as far as possible.
A couple of notes:
- Slightly strangely, this board did used to work but now is not working. However, after reseating the SOM one time one of the USB ports is then working again (one is still not)
- Swapping SOMs shows me the problem follows the carrier not the SOM
I am concerned that this might indicate some type of underlying issue with the design. Do you have any experience with this type of problem? Maybe someone has seen something similar? Could this be an issue with the SOM seating into the SODIMM connectors?
Which carrier board you are using?
Yes, design also reviewed by @matthias.tx. Do you ever see similar problems with the connectors or usb in particular?
Ok I will take another look at it.
I have imaged the signal on our USB bus and it looks like the USB_P signal is not pulling down correctly. I have sent the board to be x-ray’d, all suggestions welcome.
which USB port are you talking about.
USB_1 is the plot but I have seen the problem on both ports.
anything new from the Xray ?
I took a look at your schematic and I csaw that you have 2.2 K Ohm resistor in your signal path.
It is not clear to me why. can you provide what your thought was behind it or if this is recommend by the hub maker?
Also did you try the hints on the USB connection to connect directly to the USB from the verdin instead thru the hub?
could you sent us one of you carriers ?
It looks like on this board the problem was a dry joint under the USB multiplexer. We are used 2R2 on our first boards in series but it is 0R on the new ones. Signal looks good at USB 1.1 speeds but I cannot measure at 480 Mbps with the kit I have. I may try to do that or @gauravks has a solution to fix the speed at the low rate which is all we need anyway. Maybe that is simpler.
so does the connection work at 480 Mbps? Or you just don’t have the tools to measure it?
It seems to work well, no problems reported by the device but I do not have a suitable active differential probe to make the measurement.