Problems w/ serial flow control
Rick Stevens
rstevens at vitalstream.com
Wed May 31 18:34:11 UTC 2006
On Wed, 2006-05-31 at 12:14 -0600, Philip Prindeville wrote:
> Tim wrote:
> > On Tue, 2006-05-30 at 21:25 -0600, Philip Prindeville wrote:
> >
> >> I'm running FC3 on an MSI-7142 (K8MM-V motherboard), and using
> >> the two serial ports on the m/b. I used the stock
> >> out-of-the-shrinkwrap settings for most hardware (except for the sound
> >> board and X drivers), and things have worked fine.
> >>
> >> But... when connecting to a router's console at 115200 with either
> >> RTS/CTS or XON/XOFF flow control, I'm seeing dropped characters.
> >>
> >
> > Looking at a friend's router, his one's serial port connection *ONLY*
> > had the three-wire type of serial connection. So his couldn't possibly
> > use hardware handshaking (RTS/CTS). Perhaps yours can't too?
> >
> > Also, check what your router says about its maximum port speeds and
> > handshaking protocols.
> >
> >
>
> It is an 8-wire connection (over RJ-45 to DB-9), and can do 115200 (max
> rate)
> with either XON/XOFF or RTS/CTS.
>
> I've tried both, and they're both lossy.
>
> The issue is on the PC as the receiver...
Remember that both ends have to agree on the flow control. If one is
running RTS/CTS and the other is XON/XOFF, you don't have flow control.
At 115K, I'd always opt for RTS/CTS...XON/XOFF requires CPU intervention
unless you have fairly sophisticated hardware. All you have to do is
be a bit pokey at responding to an interrupt and you'll drop characters.
RTS/CTS is usually done at the hardware level and is a bit more
reliable.
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- Rick Stevens, Senior Systems Engineer rstevens at vitalstream.com -
- VitalStream, Inc. http://www.vitalstream.com -
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- Blech! ACKth! Ooop! -- Bill the Cat (Outland) -
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