topic Re: LPC55S1x crystal less USB in LPC Microcontrollers

LPC55S1x crystal less USB

janpieterderuit — Thu, 14 Oct 2021 18:34:18 GMT

Hi,

I'm going to try to implement the LPC55S1x crystal less Fullspeed USB, according to TN00065.

However, I can't find anything related to crystalless USB in the mentioned example (usb_device_composite_hid_audio_unified).
Also from the technical note it's not fully clear how to implement this feature. (i.e. should I replace libpower_softabi with libfro_calib_softabi.a, or should I use both?).

Does anyone know where I can find a working example?

Thanks in advance.

Best regards,
Jan Pieter de Ruiter
Airios

Re: LPC55S1x crystal less USB

janpieterderuit — Thu, 14 Oct 2021 19:37:05 GMT

And can USB1 also be used without an external crystal (in Fullspeed mode)?
Or only USB0?
I guess USB1 can't run crystalless, since USB1_PHY needs a 16 - 32 MHz crystal oscillator, right?

Re: LPC55S1x crystal less USB

xiangjun_rong — Fri, 15 Oct 2021 07:43:22 GMT

Hi,

I agree with you, I have checked the project: lpcxpresso55s16_dev_composite_hid_audio_unified_freertos, the project just uses the 96MHz fro_hf internal clock as the USB0 device clock(which is divided by 2 so that the USB0_CLK is 48MHz). The USB device frame signal is NOT used to adjust the 96MHz fro_hf in the project.

Regarding the high speed USB1, customer has to use external clock or crystal to provide high precious clock frequency, internal FRO clock can not be used.

Hope it can help you

XiangJun Rong

Re: LPC55S1x crystal less USB

janpieterderuit — Fri, 15 Oct 2021 08:33:02 GMT

Hi XiangJun Rong,

Thanks for the quick reply.

So I'll try to figure it out myself. It doesn't look too complicated. I'll get back when I have it working.

Too bad it doesn't work with USB1, since that's the one we use on our PCB... Would have been nice when it was mentioned in the technical note (explicitly).

BR, Jan Pieter

Re: LPC55S1x crystal less USB

janpieterderuit — Mon, 18 Oct 2021 07:50:50 GMT

We decided to not implement crystalless USB for now, as USB0 is not available on our PCB, and routing restrictions will probably prevent changing that, even when we do a PCB redesign.

So I will not come back with an update about implementing it.