On Tue, Nov 1, 2022 at 12:01 PM Paul Koning via cctalk <cctalk@classiccmp.org> wrote: > > On Oct 30, 2022, at 2:49 PM, Wayne S via cctalk <cctalk@classiccmp.org> > > wrote: > > > > The difference between dz and dh interfaces is that the dh used dma instead > > of interrupts to get characters to the cpu... > > No, it doesn't. I was confused about this but was recently corrected. > > The DH11 does DMA output, but not DMA input. I don't know any DEC serial > port devices that have DMA input; it would make very little sense to do that > since input generally is one character at a time.
Yes. I was going to mention this in my previous reply but got sidetracked. The big benefit for DH11 and DMF32 and 3rd-party DH11 work-alikes (Emulex CS-21...) is that since under normal workflow, many times more chars go out than come in so DMA-out saves a lot of overhead when blasting screens of stuff (like refreshing your page in EDT...) and people don't type all that fast by comparison. Where we used to have problems is having multiple Kermit sessions on our serial ports. Those hammer both ways. Fortunately, I wasn't trying to support PDP-11s with split baud rates like 1200/150 that were used to _really_ reduce input interrupt frequency. Our machines kept up at 9600/9600. -ethan
