Re: PPP/Serial system

Al Longyear (
Wed, 3 Jul 1996 11:33:51 -0700 (PDT)

Steve Davies wrote:

> Firstly I'll try asking the following question again as I think the list
> must have lost it before. I occasionally get the error:
> ppp_toss: reason code = 4

The ppp.c driver received an error code #4 from the tty driver.

The tty driver error codes are listed in the appropriate tty include
file. I don't really remember the one off the top of my head.

HOWEVER, I do recognize the code 4. In fact, it is so common of a
question that it is specifically listed in the PPP-FAQ document.



1. Don't run an 8250 or 16450 UART at rates greater than 9600 BPS

2. Get SCSI disks with a good 'bus mastering' controller such as the
Buslogic. (I still like my Adaptec 1542b, but Adaptec 1542c is not as
good as the Buslogic and you can't get the 'b' version any longer.)

Ditch those !@#$% IDE drives or live with the occasional tossing of
the UART data.

> Secondly, I am curious to know whether the kernel fully supports the
> 16550A Serial UART ? If so, what size xmit/recv buffers does it configure
> ? I would like it to be set to 8/8 bytes as I think the above error may
> be caused by buffer overruns.

The 16550A UART is fully supported.

You probably have IDE drives. That's unfortunate (for you). The IDE code
masks the interrupts while it is doing the disk transfer to prevent the
sector from becomming corrupted. At a high speed serial link, the masking
of the interrupts is too long and you may get an occasional reciver overrun
status from the serial drivers.

The PPP system will simply toss the frame.

That is not a disaster. The frame will be resent when the ACK is not
forthcomming. It will just be unfortunate that the transfers will seem to
hold for a few seconds until the peer system times out and resends the

Al Longyear           
Finger for a public PGP key