[Bug 1891829] Re: High bit(s) sometimes set high on rcvd serial bytes when char size < 8 bits

[Michael Slade]

** Summary changed:

- High bits(s) sometimes set high on rcvd serial bytes when char size < 8 bits
+ High bit(s) sometimes set high on rcvd serial bytes when char size < 8 bits

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https://bugs.launchpad.net/bugs/1891829

Title:
  High bit(s) sometimes set high on rcvd serial bytes when char size < 8
  bits

Status in QEMU:
  New

Bug description:
  I *believe* (not confirmed) that the old standard PC serial ports,
  when configured with a character size of 7 bits or less, should set
  non-data bits to 0 when the CPU reads received chars from the read
  register.  qemu doesn't do this.

  Windows 1.01 will not make use of a serial mouse when bit 7 is 1.  The
  ID byte that the mouse sends on reset is ignored.  I added a temporary
  hack to set bit 7 to 0 on all incoming bytes, and this convinced
  windows 1.01 to use the mouse.

  note 1:  This was using a real serial mouse through a passed-through
  serial port.  The emulated msmouse doesn't work for other reasons.

  note 2:  The USB serial port I am passing through to the guest sets
  non-data bits to 1.  Not sure if this is the USB hardware or linux.

  note 3:  I also needed to add an -icount line to slow down the guest
  CPU, so that certain cpu-sensitive timing code in the guest didn't
  give up too quickly.

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