topic Re: USB2.0 drive strength setting in i.MX Processors

USB2.0 drive strength setting

Shao — Mon, 18 Oct 2021 02:56:06 GMT

Hi,

Our chip is imx8mq(google-coral). We are facing EMI issues on USB.

The USB port only work as USB2.0 in our project and we are trying to decrease usb drive strength.

We read the imx8qm ApplicationsProcessorsReferenceManual. There is a register USBPHY_TXn can change the amplitude of the High Speed Tx output.

But that register doesn't exist in imx8mq. Does it miss in the imx8m ApplicationsProcessorsReferenceManual?

We only find the related register "PHY_CTL3_ADDR" can change setting to compensate for added
series resistance on the USB.

We change the value of TXRESTUNE0 but can't see any effect.

Are there any other register can change USB drive strength?

Re: USB2.0 drive strength setting

igorpadykov — Mon, 18 Oct 2021 05:26:20 GMT

Hi ShaoHao

i.MX8MQ is different from i.MX8QM, please look at

https://www.nxp.com/products/processors-and-microcontrollers/arm-processors/i-mx-applications-processors/i-mx-8-processors/i-mx-8m-family-armcortex-a53-cortex-m4-audio-voice-video:i.MX8M?tab=Documentation_Tab

For adjusting usb one can look at AN12409 i.MX6/7/8 series USB Certification Guide

sect.8.4 i.MX8M USB PHY Registers and Software Configurations

Best regards
igor

Re: USB2.0 drive strength setting

Shao — Tue, 19 Oct 2021 06:28:41 GMT

I read the section 8.4.4.2.
The content is description same thing in the Applications Processors Reference Manual 11.1.3.2.7.
Is that only register to modify USB strength?

I set TXRESTUNE0 to 00b and TXPREEMPULSETUNE0 to 1b. Is the setting for lowest USB drive strength?