Virtual COM PORT issue

[jparrish88]

We have a high priority problem that we are hoping you can help us resolve quickly. We can't get USB virtual comm port working on our microcontroller (PK60FN1M0) with MQX (not lite). We have one 8MHZ crystal oscillator on OSC0 that we create a 120MHz PLL0 generated system clock from. We have verified the 120MHz clock creation by sending UART comm to a terminal program on our PC correctly. From this point, we can't get the USB virtual comms working.

Using the TWR-K60F120M we can communicate using the virtual USB comm example that comes with MQX. The difference here is that the TWR uses a 50MHz oscillator on OSC0, a 12MHz on OSC1 and a 32.768k on OSC32. We believe the system clock is 120MHz generated from the 50MHz OSC0 clock. The USB clock is then generated from the 120MHz PLL0 generated system clock just like our custom case.

So if the USB comms both depend on the 120MHz system clock, then where is the problem originating between the two examples? Are we wrong in assuming that the USB only depends on the 120MHz generated clock?

[bobpaddock]

Most USB Cores run at 48 MHz.  Such as 96 MHz divided by two.  120 MHz is a division of 2.5 to get 48 MHz.  USB want to see a 12 MHz bus clock typically.  120 MHz divided by 100 doesn't sound correct to get 12 MHz in this case.

[jparrish88]

It turns out a wire wasn't placed correctly.