21 Nov
2017
21 Nov
'17
2:41 a.m.
So tape I can see being more weird, but isn't raw disk just "don't put it
in buffer cache"?
From what I've been able to gather early tape in
Unix was dicey, something
about the driver doing seek. Was there more to it than
that?
On Tue, Nov 21, 2017 at 02:33:55AM +0000, Clem Cole wrote:
It???s not so much that they don???t mix, it???s not
quite the same. Some
coprocessor ideas work really well into the Unix I/O model, others don't.
Raw disk and tape I/O ala a PDP11 or VAX for instance is not easy on an
IBM channel controller or a CDC PPU.
On Mon, Nov 20, 2017 at 6:45 PM Larry McVoy <lm(a)mcvoy.com> wrote:
--
---
Larry McVoy lm at mcvoy.com http://www.mcvoy.com/lm
On Mon, Nov 20, 2017 at 06:43:28PM -0500, Ron
Natalie wrote:
had
--
Sent from a handheld expect more typos than usual I get that PDP-11 and VAX used memory mapped I/O
but was that somehow
exposed above the device driver layer? If so, I missed that,
because I no conceptual or technical problem with talking
to an I/O
You
channel, it was pretty easy. And I suck at
writing drivers.
There's nothing that restricts a device driver to memory mapped I/O. do what ever you have to do to initiate the I/O.
Even the x86's
originally
used special instructions to start the I/O
(in/out). The DENELCOR HEP
supercomputer (we did this port around 1983) we had to bounce I/O
requests
off a separate I/O processor different from where
the kernel was running.
Similar constucts were used on other machines.
Yeah, that's what I thought. But other people were saying that I/O
processors and Unix didn't mix. I don't get that, seems like whatever
the model is is hidden under the driver, that's the whole point of the
driver design is it not?
29 Nov
29 Nov
10:42 p.m.
New subject: UNIX on S/370
On Mon, 20 Nov 2017, Larry McVoy wrote:
So tape I can see being more weird, but isn't raw
disk just "don't put
it in buffer cache"?
DMA too, hence the process is locked in core. I think the read/write had
to be a multiple of 512 bytes as well (I lost my Edition 6 manuals along
with my treasured -- and original! -- Lions books in a house move).
From what I've been able to gather early tape in
Unix was dicey,
something about the driver doing seek. Was there more to it than that?
IIRC, the driver kept track of the current block under the head, and
issued forward/backward skips accordingly; I have no idea whether SimH
gets that right (as opposed to doing a random seek).
(It bloody well worked, Mr Minnich, OK?)
--
Dave Horsfall DTM (VK2KFU) "Those who don't understand security will
suffer."
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