LPC Link debug probe uses too much USB bus time, breaks other devices on the USB hub

michaelstapelbe — Sun, 02 May 2021 16:20:14 GMT

I’m using the LPC-LINK2 CMSIS-DAP V5.361 firmware on my NXP LPC-Link2 debug probe.

I noticed that when I have the LPC-Link2 plugged into my USB hub, my webcam (Logitech C920) no longer works, even when these 2 devices are the only devices plugged into the 8-port USB hub, and even when not using the LPC-Link2 actively (only plugged in)! In my Linux kernel log, I see messages like:

kernel: usb 1-13.2: Not enough bandwidth for new device state.
kernel: usb 1-13.2: Not enough bandwidth for altsetting 11

In the Linux debug file /sys/kernel/debug/usb/devices, I can see the configuration based on the LPC-Link2 USB device descriptor:

T: Bus=01 Lev=02 Prnt=09 Port=02 Cnt=02 Dev#= 30 Spd=480 MxCh= 0
Ver= 2.00 Cls=ef(misc ) Sub=02 Prot=01 MxPS=64 #Cfgs= 1
P: Vendor=1fc9 ProdID=0090 Rev= 1.00
S: Manufacturer=NXP Semiconductors
S: Product=LPC-LINK2 CMSIS-DAP V5.361
C:* #Ifs= 5 Cfg#= 1 Atr=80 MxPwr=500mA
A: FirstIf#= 1 IfCount= 2 Cls=02(comm.) Sub=02 Prot=00
I:* If#= 0 Alt= 0 #EPs= 2 Cls=03(HID ) Sub=00 Prot=00 Driver=usbhid
E: Ad=81(I) Atr=03(Int.) MxPS=1024 Ivl=125us
E: Ad=01(O) Atr=03(Int.) MxPS=1024 Ivl=125us
I:* If#= 4 Alt= 0 #EPs= 2 Cls=03(HID ) Sub=00 Prot=00 Driver=usbhid
E: Ad=84(I) Atr=03(Int.) MxPS=1024 Ivl=250us
E: Ad=04(O) Atr=03(Int.) MxPS=1024 Ivl=250us
I:* If#= 1 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=02 Prot=00 Driver=cdc_acm
E: Ad=83(I) Atr=03(Int.) MxPS= 16 Ivl=1ms
I:* If#= 2 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=cdc_acm
E: Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 3 Alt= 0 #EPs= 2 Cls=03(HID ) Sub=00 Prot=00 Driver=usbhid
E: Ad=85(I) Atr=03(Int.) MxPS= 64 Ivl=500us
E: Ad=05(O) Atr=03(Int.) MxPS= 64 Ivl=500us

I am surprised to see the large packet size of 1024 bytes for interface 0 and 4 (USB HID). Can this high max packet size value be lowered to the actual packet size, or are the interrupt packets really this big? For USB HID, I would have expected 64 bytes max packet size.

Also, the minimum interval of 125μs for the endpoints on interface 0 means that the device consumes bus time in every single USB micro frame. Can the interval be set higher, e.g. to 1ms like for interface 1?

These should be 2 quick changes to the USB device descriptor, that hopefully fix the compatibility issue that the current descriptor causes.

I am happy to test an updated firmware if you want to send me one.

Thank you for taking a look

Re: LPC Link debug probe uses too much USB bus time, breaks other devices on the USB hub

converse — Sun, 02 May 2021 21:11:36 GMT

CMSIS-DAP is a standard from ARM, NXP just port it to their hardware.

you could try a JLink firmware for LPC-Link to see if that changes the behaviour. use Lpcscrypt to do this. See https://www.nxp.com/design/microcontrollers-developer-resources/lpc-microcontroller-utilities/lpcscrypt-v2-1-2:LPCSCRYPT

topic LPC Link debug probe uses too much USB bus time, breaks other devices on the USB hub in LPC Microcontrollers

LPC Link debug probe uses too much USB bus time, breaks other devices on the USB hub

Re: LPC Link debug probe uses too much USB bus time, breaks other devices on the USB hub