• It was observed that Windows 2003 x64 hangs when shutting down if an
    RTL8139 NIC and a USB device tablet are both present.  What seems to be
    happening is:
    
    - the guest shuts down the transmitter and receiver
    - time passes
    - the guest requests a tally counter dump
    
    As it happens, the tally counter command register overlaps the transmit
    status register in C mode.  Qemu determines whether the chip is in C or C+
    mode by looking at the C+ transmit enable bit; as this is now unset, the
    dump tally counter command is interpreted as a C mode transmit command.  The
    guest doesn't think so, however, and continues to poll for completion of the
    tally counter dump command.  This never occurs, so the guest hangs.
    
    Fix by redefining C+ mode as "a write to the C+ command register has occurred
    since the last reset".  The data sheet is silent on the matter.
    
    Signed-off-by: Avi Kivity <avi@redhat.com>
    Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
    
    
    
    git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6279 c046a42c-6fe2-441c-8c8c-71466251a162
    aliguori authored
     
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