SUMMARY DTR Still Dropping

From: Ron Henderson (
Date: Mon Oct 19 1992 - 13:53:36 CDT

Dear Sun Managers,

Original Question:

>A while back i wrote that i was having problems with my DTR signal staying low
>every once in a while on ttya on a Sparc station 2 running 4.1.2. I have getty
>running on ttya and i am also ru>nning uucp for mail and file transfers twice an hour.
>Sun managers wrote back and suggested a sun jumbo patch which includes patch numbers:
> 100225-02, 100194-02, 100397-01, 100188-02, 100358-01, 100414-01.
>This was suppose to fix Bug ID:1060689 which stayes:
>When a port is used for dialing in and dialing out, DTR would be dropped
>and processes remain in <exiting> state with data queued for the driver.
>Problem: I am still having DTR staying low after a dialin or uucp session. The only
>recourse is to hangup init or kill the getty process. The problem is occuring much
> less frequently since i installed the jumbo patch, but it is still occurring.
>As you might expect you can not dialin when DTR is low!
>Does any one else have anymore thoughts (conflict between getty and uucp)?


The fix so far was to patch the kernel so that DTR would drop for a longer period of
time so that the connecting modem could hang up the connection by dropping CD.

Don Lewis from: writes:

Try patching the kernel variable zsadtrlow to a bigger number. This sets
the time that DTR is held low after the port is closed. The default is
3 (3 seconds). If the port is closed to hang up the modem, DTR is dropped,
but sometimes CD from the modem takes a while to go away. If DTR comes
back before CD is low, then it seems to confuse getty (it sort of thinks
there is an incoming call and gets about half started before CD drops).
Sometimes getty just silently hangs, sometimes it logs funny messages.
I cranked zsadtrlow up to 6 and haven't had a bit of trouble since.

John Harkins provides the two procedures:

           1) patching the kernel on the fly:
              # adb -w -k /vmunix /dev/mem
               zsadtrlow/W 6
               zsadtrlow?W 6

        - or -

           2) patching object files and make a new kernel
              # cd /usr/sys/sun4c/OBJ
              # adb -w zs_async.o
              zsadtrlow?W 6

                                --- Ron Henderson (rwh)
                                LightNET, Inc. - A UNIX and Networks Company

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