[Qemu-devel] [Bug 1086745] [NEW] serial port data THRE comes too early

[Kees Schoenmakers]

Public bug reported:

When using a serial port with a Linux guest (and host) and the
application uses hardware handshake, this fails because the handling of
TEMT and/or THRE is not operating properly in such cases.

As long as it takes _time_ for the 'real' port to output the data TEMT
may not return true. After writing characters to a real port, the driver
should timeout the transmission and after the total time expired, TEMT
can be set.

Some applications i.e. with a simplex modem do: RTS_on, WRITE_data, repeat 
IOCTL(GET_LSR_INFO), RTS_off, READ_data.
At the moment this fails because very early in the transmission, GET_LSR_INFO 
returns true and the modem transmitter is switched off.

I looked in the source (git)  and found that 'char_transmit_time' is present. 
My skills fail to implement it myself.
I build and ran the latest git version and found it to fail as decribed above.  
I hope someone can solve it.

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: handshake port serial

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https://bugs.launchpad.net/bugs/1086745

Title:
  serial port data THRE comes too early

Status in QEMU:
  New

Bug description:
  When using a serial port with a Linux guest (and host) and the
  application uses hardware handshake, this fails because the handling
  of TEMT and/or THRE is not operating properly in such cases.

  As long as it takes _time_ for the 'real' port to output the data TEMT
  may not return true. After writing characters to a real port, the
  driver should timeout the transmission and after the total time
  expired, TEMT can be set.

  Some applications i.e. with a simplex modem do: RTS_on, WRITE_data, repeat 
IOCTL(GET_LSR_INFO), RTS_off, READ_data.
  At the moment this fails because very early in the transmission, GET_LSR_INFO 
returns true and the modem transmitter is switched off.

  I looked in the source (git)  and found that 'char_transmit_time' is present. 
My skills fail to implement it myself.
  I build and ran the latest git version and found it to fail as decribed 
above.  I hope someone can solve it.

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