🚀 go-pugleaf

In article <1992Oct15.210722.26773@isrc.sandia.gov> ceschel@isrc.sandia.gov (Chad E. Schell) writes:

>Do anyone know of a way to flush the receive buffers
>of the OS/2 2.0 com drivers?  I need to do this
>in order to make sure that I am receiving recent
>data from a constant stream that I sample only at
>intermittent periods.

If you are truly only issuing I/O calls to the COM port periodically,
then you could make an initial IOCtl call (68H) to query the number of
characters in the receive queue, and then issue a read request for
just that many characters, so you don't block, but you get them all.

Personally though, I think that whenever you are dealing with the COM
port, you really should dedicate a thread to *always* be blocked ready
to read data from the port, and stick it into your own internal
buffer.  The queue of the COM driver isn't all that large (a K or two
maybe), and if you don't check soon enough you can lose data.

Now the one "problem" is that by default, if you issue a read for n
characters, it will block until you get all n characters, which is
presumably not what you want.  The best thing to do is to use a
different read timeout mode - "Wait-For-Something".  Use the Set DCB
IOCtl (53H) to enable wait-for-something read timeout processing.  In
this mode, a read to the COM device will block if nothing is
available, but will return as soon as something shows up, returning as
much data as showed up.  You can then buffer that data locally, and
return to request more.  If no data shows up for the full read timeout
period (default=1min), then the read will return anyway with 0 bytes,
and you can just loop back and issue the read again.  You can also
adjust the actual read timeout if you'd like.

--
-- David
--
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