From mboxrd@z Thu Jan 1 00:00:00 1970 From: lm@mcvoy.com (Larry McVoy) Date: Mon, 20 Nov 2017 15:45:15 -0800 Subject: [TUHS] UNIX on S/370 In-Reply-To: <05af01d36259$5e0873e0$1a195ba0$@ronnatalie.com> References: <201711200350.vAK3omwQ013495@freefriends.org> <20171120195618.GK9146@mcvoy.com> <05af01d36259$5e0873e0$1a195ba0$@ronnatalie.com> Message-ID: <20171120234515.GB9093@mcvoy.com> On Mon, Nov 20, 2017 at 06:43:28PM -0500, Ron Natalie wrote: > > > > 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. 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?