how to write a hid keyboard firmware with "low speed"

[auftrag2021]

Hardware: imxrt1170 EVK

IDE: MCUXpressor 11.7.1

SDK: 2.13.1

Imported example: evkmimxrt1170_dev_composite_hid_mouse_hid_keyboard_bm_cm7

the example itself is good, when I run it, I can see the rt1170evk play a role like mouse and keyboard which communicate with my PC usb host.

But my intension is learning the USB low level driver in very detail (signal in physical layer). Unfortunately I don't have any high-end oscilloscope to see the high speed (480MHz) eye diagram. That's why I want to degrade the USB speed in this example from HS to FS or better LS.

anyone can help to figure out how to setup the speed in the code?

[EdwinHz]

Hi @auftrag2021,

Neither of the USB cores support running on Low Speed when in peripheral (or device) mode, as described on section "62.2.2 Features" of the Reference Manual.

That said, you can set the USB core to run at Full Speed by setting the Port Force Full Speed Connect (PFSC) bit of the Port Status & Control (PORTSC1) register. That is bit 24 of this register. In the enumeration process, the device and will negotiate with the host to achieve the highest port speed by default, but setting this bit will prevent this. So, set this bit before the device is enumerated, and once connected you should see it running at Full Speed.

BR,
Edwin.

[auftrag2021]

thank you so much for the feedback

as you mentioned: the LS is really not supported by the USB controller core0/core1

I made a study in detail and finally figured out why:

The both USB transmitter don't have any pull-up option for D- line, which is required for LS detection. What a pity!

as you mentioned, we could force the bus working with FS

but I still have one thing not clear, should we activate the 1.5k pull-up resistor in USBPHY layer right?

I think it should be mandatory for the FS detection