USB CDC

Posted on May 17, 2011 at 13:05

Hi,

I am using the latest version of ST's ''Virtual COM Port'' demo to implement a small USB powered device with USB CDC support.

I have some questions/problems:

(1) In USART_To_USB_Send_Data() there is no flow control. What happens,

if the PC does not read out the buffer fast enough? How can I check

that the complete buffer has been transferred to the PC and that I

can copy the next 64 bytes to the buffer?

(2) On the evaluation board there is a ''USB_Disconnect'' line, which

disconnects the STM32 from the USB bus. Is this necessary for a

USB powered device?

(3) I am using the STM3210E-EVAL board. If the board is self powered and

connected to the PC via USB when the firmware is started,

the demo does not work as expected. It never goes to the ''Reset''

code, which sets the buffer pointers.

If I connect the USB connector to the PC, when the firmware is

already running, everything works as expected. How can I fix this

problem?

It never