From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,HTML_MESSAGE,MAILING_LIST_MULTI, RCVD_IN_DNSWL_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from minnie.tuhs.org (minnie.tuhs.org [45.79.103.53]) by inbox.vuxu.org (OpenSMTPD) with ESMTP id dbac3b9e for ; Fri, 10 Jan 2020 22:19:08 +0000 (UTC) Received: by minnie.tuhs.org (Postfix, from userid 112) id 2045A93D85; Sat, 11 Jan 2020 08:19:07 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id CE49F93DA0; Sat, 11 Jan 2020 08:18:32 +1000 (AEST) Authentication-Results: minnie.tuhs.org; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b="NAD1uvOJ"; dkim-atps=neutral Received: by minnie.tuhs.org (Postfix, from userid 112) id 398CA93DA0; Sat, 11 Jan 2020 08:18:30 +1000 (AEST) Received: from mail-ot1-f52.google.com (mail-ot1-f52.google.com [209.85.210.52]) by minnie.tuhs.org (Postfix) with ESMTPS id 82A7C93D85 for ; Sat, 11 Jan 2020 08:18:29 +1000 (AEST) Received: by mail-ot1-f52.google.com with SMTP id i15so3492343oto.2 for ; Fri, 10 Jan 2020 14:18:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to; bh=+aMkIH7fws9rCNesDRvUmSxTdu/ES0Ufvqk+ZYrdhz4=; b=NAD1uvOJVsevsInrkiWScX8yVirxIA/NYoXwTSM3fhL3Fcyx+mRDnqTDtskubHi+Iy slfbKOsRvFjFAqZzea/BopJsoV9nt8fNMXfEgC883SSdpjDj0IclOs47el3Kf6gJWxrE Ots96nzlZvR8OMModLJfAwUnm/rM7SScdzeb/l1MNLZQaxjhHlXpnVI2xwmyOHcPYS82 dSUFterxknEEOmJrHoATQ3VMY/Vhw89Om6lcqOZJP7XHuO5edKOFiV7JKn1byELcgF5n N010Ier/sdnbjvKGGjMNBP0rJgpbQHCPQEsaCH13vFQA/tztQpPhpXSkgeJTJGtVWvpd Yjrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=+aMkIH7fws9rCNesDRvUmSxTdu/ES0Ufvqk+ZYrdhz4=; b=UjqG1Nsv4U5HUXvu0nh4e4/aWvDzuFOOGCXtqA4fplkqDIbgoV9ZHpa7XWO4iOgno9 67Grj1jQ7soVWtt13H2w9QkV/Ke6Mmb/IvNvW0XOxzBnh/32yZ1s8btWHdEbPsla1Hi5 zSgBx9dkxlZbFDtwWeeDTlS6v8IY1VqQJUYU63jepvkL/E1i+CVp1w4Ar4m1cAiIyLzt Kcu6L7AboTHSEQD7XUm+gw3NjLuf8bWAKtf26ctu31Aux775AoEA4s6fl1mtO/jrOy8k idAFQVU2v0RQvIqc12s1hPXKFQyJ8s9PfN89jiBpGoanGEm7syMum4J1TSj5ZIiDpgqp aPPw== X-Gm-Message-State: APjAAAX8UChpd0rAEzdgnv72wAUAhFRRWGcKVteKbF/piMxqIT5Ix6ra 4Xw1kBvvokc1ZiNlkEe6zDteiK5L+bRoZZV8iNQz2msy X-Google-Smtp-Source: APXvYqxD//HKNh9nPBFsJ5UktvRnhKml7gY1zccUiIn/aqf0U9FHS/rDd9bdx8+znjclIA3lHNUAo6l/LHO6h9RzqPM= X-Received: by 2002:a9d:74c8:: with SMTP id a8mr4217748otl.57.1578694708589; Fri, 10 Jan 2020 14:18:28 -0800 (PST) MIME-Version: 1.0 References: <9c507ef665851fd21ecdf0e23136dc86@firemail.de> <1ippPk-8PE-00@marmaro.de> <81cf0f73-2141-10c9-7352-51c0aac76959@mhorton.net> In-Reply-To: From: Adam Thornton Date: Fri, 10 Jan 2020 15:18:17 -0700 Message-ID: To: TUHS main list Content-Type: multipart/alternative; boundary="0000000000005077e9059bd081d4" Subject: Re: [TUHS] screen editors / machine load X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" --0000000000005077e9059bd081d4 Content-Type: text/plain; charset="UTF-8" A) The original WD UART chip had very limited buffering. The timing was such that as high rates it could not empty accept a second character without the first being overwritten. This was a long-standing issue for many UARTs long in the 1990s. The original chip NS built and IBM used on the PC (the NS8250) was notorious for the same problem. By the time of Motorola's 6881, it had 8 characters of buffering IIRC. Great, now I'm having flashbacks to upgrading my 4-port serial card with 16450s and then 16550s in the early 90s. On Fri, Jan 10, 2020 at 8:49 AM Clem Cole wrote: > > > On Fri, Jan 10, 2020 at 10:00 AM Mary Ann Horton wrote: > >> Yes, it was a real concern. Physical memory on the shared PDP-11 was >> limited, and if everyone had a separate copy of vi running the machine >> would swap itself silly. >> >> This only mattered if everyone had their own separate copy of vi >> installed. The fix was to put vi in a single system directory, such as >> /usr/ucb or /exptools. The instruction part of its memory would be >> shared among all the users, resulting in much less swapping. >> > Actually it was much worse than that... > > What Mary Ann points out was mostly true of your PDP-11 had DH11's > installed; which had deeper hardware buffering and 16 character DMA on > output. But these were expensive from DEC and also took up a 'full system > unit' in the CPU for 16 lines. Until Able (much later) released the > DMAX-11 (*a.k.a.* DH/DM) product of a DH11 clone on a single board, many > university sites did not use them; but used multiple DL-11/KL-11's instead. > > If your system was configured with DL/KL11s or similar (CMU had it's own > called 'ASLIs' - a synchronous line interfaces) each character took one > interrupt for each either input or output. Moreover, the UARTS that DEC > used which were made by Western Digital had 2 >>or less<< characters of > input buffering, so they could drop chars[1]. The ASLI's used a later chip > with a slightly better buffer IIRC but I admit I've forgotten the details > (Jim Tetter probably remembers them). > > So if you had a single line, the interrupt load was huge on a PDP-11. For > this reason, a lot of sites limited glass TTYs to speeds like 2400 or 4800 > baud, not the full 9600. > > DEC later released the DZ-11 which worked on units of 8 ports per board. > Unfortunately, it was not DMA and the buffering was still pretty shallow. > Joy did a lot of work on 4.1BSD in the DZ driver to cut down the > interrupts because 9600 baud DZ lines could swamp a vax and when running > the BerkNet between systems (before UCB had ethernet), 9600 baud serial > lines were standard. > > > [1] Two things > A) The original WD UART chip had very limited buffering. The timing was > such that as high rates it could not empty accept a second character > without the first being overwritten. This was a long-standing issue for > many UARTs long in the 1990s. The original chip NS built and IBM used on > the PC (the NS8250) was notorious for the same problem. By the time of > Motorola's 6881, it had 8 characters of buffering IIRC. > > B) As I understand the history, Gordon developed the original idea of the > UART at DEC for the PDP-1. But I'm not sure of the patent details. He does > not list the UART patent on his web site although he does mention inventing > it. I have been under the impression CMU was somehow mixed up in the > patent and licensing of it, *i.e.* WD got the license from CMU to make > them not DEC; which was part of why we had the ASLI's. Again, IIRC, we got > the UART chips from WD at cost and could make the ALSI's locally much > cheaper than DL-11s. >>I think<< the story was that one of Gordon's > student's designed a chip, which WD fabbed and licensed. Before that DEC > had built UARTs on boards from transistors and later logic gates. > > --0000000000005077e9059bd081d4 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
A) The original WD UART ch= ip had very limited buffering.=C2=A0 =C2=A0The timing=20 was such that as high rates it could not empty accept a second character without the first being overwritten.=C2=A0 This was a long-standing issue= =20 for many UARTs long in the 1990s.=C2=A0 The original chip NS built and IBM= =20 used on the PC (the NS8250) was notorious for the same problem.=C2=A0 By th= e=20 time of Motorola's 6881, it had 8 characters of buffering IIRC.

Great, now I'm having flashbacks to upgrading my 4-po= rt serial card with 16450s and then 16550s in the early 90s.

=

On Fri, Jan 10, 2020 at 8:49 AM Clem Cole <clemc@ccc.com> wrote:


On Fr= i, Jan 10, 2020 at 10:00 AM Mary Ann Horton <mah@mhorton.net> wrote:
Yes, it was a real concern. Physic= al memory on the shared PDP-11 was
limited, and if everyone had a separate copy of vi running the machine
would swap itself silly.

This only mattered if everyone had their own separate copy of vi
installed. The fix was to put vi in a single system directory, such as
/usr/ucb or /exptools. The instruction part of its memory would be
shared among all the users, resulting in much less swapping.
Actually it was much worse than that...
What Mary Ann points out was mostly true of your PDP= -11 had DH11's installed; which had deeper hardware buffering and 16 ch= aracter DMA on output.=C2=A0 =C2=A0But these were expensive from DEC and al= so took up a 'full system unit' in the CPU for 16 lines.=C2= =A0=C2=A0 Until Able (much later) released the DMAX-11 (a.k.a. D= H/DM) product of a DH11 clone on a single board, many university sites did = not use them; but used multiple DL-11/KL-11's instead.

If your system was configured=C2=A0with DL/KL11s or simi= lar (CMU had it's own called 'ASLIs' - a synchronous line inter= faces) each character took one interrupt for each either=C2=A0input or outp= ut.=C2=A0 Moreover, the UARTS that DEC used which were made by Western Digi= tal had 2 >>or less<< characters of input buffering, so they co= uld drop chars[1].=C2=A0 The ASLI's used a later chip with a slightly b= etter buffer IIRC but I admit I've forgotten the details (Jim Tetter pr= obably remembers them).

So if you had a single line, t= he interrupt load was huge on a PDP-11.=C2=A0 For this reason, a lot of sit= es limited glass TTYs to speeds like 2400 or 4800 baud, not the full 9600.= =C2=A0 =C2=A0

DEC later released the DZ-11 which worke= d on units of 8 ports per board.=C2=A0 Unfortunately, it was not DMA and th= e buffering was still pretty shallow.=C2=A0 =C2=A0Joy did a lot of work on = 4.1BSD in the DZ driver to cut down the interrupts because 9600 baud DZ lin= es could swamp a vax and when running the BerkNet between systems (before U= CB had ethernet), 9600 baud serial lines were standard.

<= div class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif= ">
[1]=C2=A0 Two things
=C2=A0A) The original WD UART c= hip had very limited buffering.=C2=A0 =C2=A0The timing was such that as hig= h rates it could not empty accept a second character without the first bein= g overwritten.=C2=A0 This was a long-standing issue for many UARTs long in = the 1990s.=C2=A0 The original chip NS built and IBM used on the PC (the NS8= 250) was notorious for the same problem.=C2=A0 By the time of Motorola'= s 6881, it had 8 characters of buffering IIRC.

B) As I= understand the history, Gordon developed the original idea of the UART at = DEC for the PDP-1. But I'm not sure of the patent details. He does not = list the UART patent on his web site although he does mention inventing it.= =C2=A0 =C2=A0I have been under the impression CMU was somehow mixed up in t= he patent and licensing of it, i.e. WD got the license from CMU to m= ake them not DEC; which was part of why we had the ASLI's.=C2=A0 Again,= IIRC, we got the UART chips from WD at cost and could make the ALSI's= =C2=A0locally much cheaper than DL-11s.=C2=A0 >>I think<< the s= tory was that one of Gordon's student's designed a chip, which WD f= abbed and licensed.=C2=A0 Before that DEC had built UARTs on boards from tr= ansistors and later logic gates.

--0000000000005077e9059bd081d4--