[U-Boot] does u-boot support usb client and how does usbtty works on it?

[wind hunter]

?Hi,

I am working on a PXA270 based custom board which has a serial port and a USB port as its interfaces.  And, I would like to use u-boot as my boot loader.  Due to PCB space limitation, we only wired the USB client support only on it.   Thus, I do not have a way to use the USB host functions.  But, we know its USB client port worked as a HID device in our previous PCB design iteration.

I have successfully modified the colibri_pxa270 configuration of u-boot to boot up my board serially.  And, I am having trouble getting the USB client port function to work on it.  I have followed the u-boot Readme instructions to #define CONFIG_USB_DEVICE, CONFIG_USB_TTY, and CONFIG_SYS_CONSOLE_IS_IN_ENV on my modified colibri_pxa270.h file.  And, I have also #undef CONFIG_CMD_USB since I do not have USB Host support on this board whatsoever.

To my best knowledge on this that if those three defines are #defined in my configuration file and "setenv stdin=usbtty; setenv stdout usbtty", the USBTTY functions will bring to live on the board.  But in reality, it shows up as a "Unknown Device" on my PC even though I have set my board up as "usbtty=cdc_acm" and got the correct VBus pull up GPIO pin setup.

So, does u-boot supports USB client or not?  From the documents on my u-boot source code, u-boot-v2010.09, it should support both functions.

If u-boot does support USB client mode, what are the steps I have to take for it to work on my PXA270 based board?   All I want is a USB to work like a serial port like a serial console!.  Do I have to enable interrupts on my boards to in order to do it?  Or, I can do polling?

How dose the USBTTY stuff getting called after all anyway?  Base on my best code tracing abilities, I can see it is stdio_register() all the usbtty handlers.   But what comes next is not really clear to me.  Can someone answer this for me?  How does those usbtty_xxx() get utilized?

Thanks.