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USB CDC - Issue with size buffer in EP0 OUT

Question asked by Witte on Aug 28, 2015
Hello everybody,

I'm using USB CDC in my project with STM32L151CC, and I got little issue with the USB Library.

I know that the MAX SIZE of EP0 buffer to transmission is 64 bytes.

In my debugs, I could send 1 byte, 2 bytes, 63 bytes, 65 bytes or X bytes. But when I sent exactly 64 BYTES into the buffer, the USB CDC don't sent. These 64bytes only was sent when I send a new byte, adding more than 64 bytes into buffer of the end point.

Why this happens? 
Anyone have this trouble with the USB CDC?

I'm using HAL Lib with ST CUBE.

Thank you very much!