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Article #478Re: open(2) doesn't block on DCD
From: Mark A. Tarbell
Date: Wed, 08 Apr 1992 00:20
Date: Wed, 08 Apr 1992 00:20
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In article <3347@starlab.UUCP> st@starlab.UUCP (Stefan Taxhet) writes: > But getty doesn't block! > My little program using open(2) doesn't either! > > To test this I removed the modem (DCD shouldn't be asserted then?), > but the same result... Stefan: open(2) does indeed block as advertised, but only if you have a device connected to the port which ties the DCD pin LOW (ground state). By default, the port will float DCD HIGH (asserted or "true")... To simulate this, connect the DCD pin to ground via a dropping resistor (say 1k ohm). voila! open blocks. Disconnect the resistor and voila! the open goes through. Check what your attached device does. You may be surprised. I went 'round on this one until I figured out what was happening. But it really does work when set up correctly! Mark Tarbell (suite!tarbell@uunet.uu.net) or (tarbell@suite.com)
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Path: arc1-ca.pugleaf.net!sparky!uunet!suite!uunet.uu.net From: suite!tarbell@uunet.uu.net (Mark A. Tarbell) Newsgroups: comp.sys.next.sysadmin Subject: Re: open(2) doesn't block on DCD Message-ID: <230@suite.uunet.uu.net> Date: 8 Apr 92 00:20:44 GMT References: <3347@starlab.UUCP> Sender: tarbell@suite.uunet.uu.net Reply-To: suite!tarbell@uunet.uu.net Lines: 21