21 Nov
2017
21 Nov
'17
12:45 a.m.
On Mon, Nov 20, 2017 at 06:43:28PM -0500, Ron Natalie wrote:
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?
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 had
no conceptual or technical problem with talking to an I/O
channel, it was pretty easy. And I suck at
writing drivers.
There's nothing that restricts a device driver to memory mapped I/O. You
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.