usb enumeration fail on beagleboard

hardware: two arm boards (e.g. a panda and a beagle xm), a usb to mini usb cable

testing scenario: power both boards with external power supply and

panda: let it normally boot till login prompt

beagle: stop it at u-boot prompt

then connect the usb plug to the panda board, and the mini usb to the beagle, on panda console will appear:

omap login: [ 227.659362] hub 1-1:1.0: state 7 ports 5 chg 0000 evt 0004
[ 227.666381] hub 1-1:1.0: port 2, status 0101, change 0001, 12 Mb/s
[ 228.682250] hub 1-1:1.0: debounce: port 2: total 100ms stable 100ms status 0x101
[ 228.920898] usb 1-1.2: new full speed USB device number 4 using ehci-omap
[ 229.230010] usb 1-1.2: skipped 4 descriptors after interface
[ 229.236145] usb 1-1.2: default language 0x0409
[ 229.252380] usb 1-1.2: udev 4, busnum 1, minor = 3
[ 229.257415] usb 1-1.2: New USB device found, idVendor=0525, idProduct=a4a7
[ 229.264739] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 229.272552] usb 1-1.2: Product: U-Boot 2011.03
[ 229.277282] usb 1-1.2: Manufacturer: Das U-Boot
[ 229.282043] usb 1-1.2: SerialNumber: 0000000
[ 229.287231] usb 1-1.2: usb_probe_device
[ 229.295227] usb 1-1.2: configuration #1 chosen from 1 choice
[ 229.301879] usb 1-1.2: adding 1-1.2:1.0 (config #1, interface 0)
[ 229.308990] usb 1-1.2: adding 1-1.2:1.1 (config #1, interface 1)
[ 229.340759] cdc_acm 1-1.2:1.0: usb_probe_interface
[ 229.345886] cdc_acm 1-1.2:1.0: usb_probe_interface - got id
[ 229.351928] cdc_acm 1-1.2:1.0: This device cannot do calls on its own. It is not a modem.
[ 229.360961] cdc_acm 1-1.2:1.0: ttyACM0: USB ACM device
[ 229.370269] usbcore: registered new interface driver cdc_acm
[ 229.376281] cdc_acm: v0.26:USB Abstract Control Model driver for USB modems and ISDN adapters
[ 602.088134] omapdss DISPC error: timeout waiting for EVSYNC
[ 602.189697] omapdss DISPC error: timeout waiting for EVSYNC

now, revert the roles:

beagle: make it boot till login prompt

panda: stop it at the u-boot prompt

connect the usb plug to the beagle and the mini to the panda, on beagle console will appear:

omap login: [ 14.907440] twl4030 operation mode cannot be changed on-the-fly
[ 14.982788] twl4030 operation mode cannot be changed on-the-fly
[ 22.216735] usb0: no IPv6 routers present
[ 31.685821] usb 1-2.2: new full speed USB device using ehci-omap and address 4
[ 31.779541] usb 1-2.2: device descriptor read/64, error 18
[ 31.974700] usb 1-2.2: device descriptor read/64, error 18
[ 32.170166] usb 1-2.2: new full speed USB device using ehci-omap and address 5
[ 32.263824] usb 1-2.2: device descriptor read/64, error 18
[ 32.459136] usb 1-2.2: device descriptor read/64, error 18
[ 32.654510] usb 1-2.2: new full speed USB device using ehci-omap and address 6
[ 32.695495] usb 1-2.2: device descriptor read/8, error -61
[ 32.836364] usb 1-2.2: device descriptor read/8, error -61
[ 33.037292] usb 1-2.2: new full speed USB device using ehci-omap and address 7
[ 33.078369] usb 1-2.2: device descriptor read/8, error -61
[ 33.219116] usb 1-2.2: device descriptor read/8, error -61
[ 33.334045] hub 1-2:1.0: unable to enumerate USB device on port 2

software versions used:

panda:
Texas Instruments X-Loader 1.4.4ss (Mar 18 2011 - 14:14:59)
...
U-Boot 2011.03-rc1 (Feb 09 2011 - 01:46:42)
...
flag@omap:~$ uname -a
Linux omap 2.6.38-1208-omap4 #11-Ubuntu SMP PREEMPT Fri Apr 15 16:34:35 UTC 2011 armv7l GNU/Linux

beagle:
Texas Instruments X-Loader 1.5.0 (Apr 11 2011 - 09:47:05)
...
U-Boot 2011.03 (Apr 20 2011 - 07:19:53)
...
tested kernels: Ubuntu 2.6.38-9.43-omap 2.6.38.4 and Ubuntu 2.6.35-29.51-omap 2.6.35.12