Hi, I'm trying to build an usb device conforming to the CDC ACM device class. The device uses an interrupt IN endpoint with a max packet size of 8 bytes. I tried to send a SERIAL_STATE notification to the host (to report parity errors, etc.) and noticed, that it is not handled as I would expect: Because I have to transmit the notification in two consecutive packets due to the limited packe size (SERIAL_STATE notification consists of an 8 byte header + 2 byte data), acm_ctrl_irq is called twice, too. So the notification is not reassembled before processing in acm_ctrl_irq. Of course acm_ctrl_irq only handles "garbage" in this cases because both recieved packages are to short. Obviously the max packet size of the interrup IN endpoint needs to be equal (or greater) to the size of the largest notification the CDC device may transmit, to work with the cdc_acm module. Question: Is this just a (probably quite realistic) assumption made in the current kernel code, or is this constraint defined in the usb specification? I'm new to the usb stuff and am not sure if i missed something. Additionally I am confused, because Atmel provides some documentation how to build a CDC ACM device [1], where the fragmented transmission of notifications is explicitely stated as one possible implementation. I'm using kernel 4.4.0. Tobias [1] https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad= rja&uact=8&ved=0ahUKEwjWvo- Ij5_QAhUFbRQKHUSlAa8QFggdMAA&url=http%3A%2F%2Fwww.atmel.com%2Fimages%2F doc6269.pdf&usg=AFQjCNEQ-Oz__2Dq7ueSsd1JDAceCLPIHg -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
