From mboxrd@z Thu Jan 1 00:00:00 1970 From: ron@ronnatalie.com (Ron Natalie) Date: Mon, 20 Nov 2017 18:43:28 -0500 Subject: [TUHS] UNIX on S/370 In-Reply-To: <20171120195618.GK9146@mcvoy.com> References: <201711200350.vAK3omwQ013495@freefriends.org> <20171120195618.GK9146@mcvoy.com> Message-ID: <05af01d36259$5e0873e0$1a195ba0$@ronnatalie.com> > 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.