LPC546xx minimal clock speed when using USB1 in full speed

[arno1]

We are using the USB1 (high speed USB peripheral) from the LPC54606, but we are using it in Full Speed mode (which is a lower speed than high speed).

The reference manual mentions that the system clock should be at least 60 MHz for high speed USB operation, but it is unclear to me what the clock frequency should be in case of using it in Full Speed.
Currently the system is clocked at 48 MHz and our Mass Storage Class implementation (based on the example in the MCUXpresso SDK) is working without any problems.

However we are seeing some issues with the CDC ACM implementation (also based on the example from the SDK) and I'm wondering if this might have anything to do with it, or if I need to look in a different area.

Hopefully someone can give me some background/additional information on this speed requirement.

[ZhangJennie · Accepted solution]

Hi Arno,

I was informed there is no way to force USB1 to run in full speed mode.
If you want to use USB Full speed mode, please use USB0 instead.

For USB0:

USB main clock: The USB main clock is a 48 MHz clock used for USB functions. If the FRO is used as the USB clock source, it can be configured to adjust automatically to the USB bus rate .
• CPU clock: The minimum frequency of the CPU clock is 12 MHz when the USB device controller is receiving or transmitting USB packets.

Have a great day,
Jun Zhang

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[arno1]

After digging through the SDK, I found out that the variable I had changed the initialization value of, always gets overwritten by the SDK.
We are not able to use the USB0 as we are using pretty much all available pins of the MCU in our project.

After increasing the speed the CDC ACM communication does improve, but I'm still running into some issues.