ttyACM0 only reads 64 bytes

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http://stackoverflow.com – I'm bit of a newbie but I have an legacy app that reads 64 bytes of AES encrypted data from a device using ttyACM0. I now need to read 128 bytes. Sounded simple; increase the sizes of buffers etc. But no matter what I try, I still can only read 64 bytes. After that it just hangs. I verified the communications in Windows with a terminal and cdc-acm driver. Device does not use flow control. I cant upload code because its proprietary but below are some snippets: The Intialization: CACS_RefID::Initialise() { int iRet = 1; struct termios dev_settings; if(( m_f (HowTos)