> Well, then the first question that needs to be answered, which model > of PDP-11 was that code expected to run on
ANF-10 primarily runs on the 11/40 (well, and the PDP-10s). Exceptions: DN200 remote station: 11/34, DN22: 11/04 . CHK11 compiles accordingly. On 20-Jul-20 18:19, Johnny Billquist wrote: > Well, then the first question that needs to be answered, which model > of PDP-11 was that code expected to run on, because the results will > differ depending on that. Also, what kind of memory? (I would guess > some old, small core memory boards.) > The PDP-11 execution speed really does vary based on many factors, on > real hardware... > > Johnny > > On 2020-07-21 00:13, s...@swabhawat.com wrote: >> >> >> L.S. >> >> Actually where this is important, is when using Pdp11 based ANF10 >> workstations in the Tops10 realm. >> >> When starting up, the Anf10 software on the pdp11 sim test various >> devices for functionality thereby using instruction count based loops >> etc. >> When all the devices necessary (paper tape reader/punch, incremental >> plotter interface, DZ and DH multiplexors, DMS and DUP/KDP devices >> and DL11 interfaces) are properly verified, it cranks up the >> communication configuration with scanning the network for active >> Pdp10 Tops10 host systems. >> The throttling of the pdp11 should be carefully selected to let this >> function. >> >> >> Reindert >> >> >> -----Original Message----- >> From: Simh [mailto:simh-boun...@trailing-edge.com] On Behalf Of >> Johnny Billquist >> Sent: Monday, 20 July, 2020 23:20 >> To: Paul Moore <paulmoore...@hotmail.com>; simh@trailing-edge.com >> Subject: Re: [Simh] pdp 11 timing >> >> Instruction timing as such is not relevant. Different implementations >> had very different timings, not to mention that speed of memory also >> makes a difference. >> >> Devices basically do not have a strict timing either, but yes, there >> is plenty of software that assumes that an interrupt does not happen >> before a single instruction have been executed after the previous >> interrupt, from the same device, for example. >> On real hardware that was just an absurd case that lots of code never >> considered, since it wasn't really physically possible for it to happen. >> >> The throttling in simh is because some people want the emulation to >> somewhat mimic the real thing. For some people, that experience of >> slowness is desirable. >> >> Johnny >> >> On 2020-07-20 23:10, Paul Moore wrote: >>> (I am writing my own emulator just because I have never done that >>> before, and the PDP 11 is such a pivotal system in the history of >>> modern computing it seemed worth learning about, and what better way >>> to learn than to emulate it ) >>> >>> So how important is timing of instruction execution and device >>> response? >>> >>> The PDP 11 docs go to great length giving instruction timing. But the >>> fact that there is a % throttle in simh suggest that’s not important. >>> I assume that turning that throttle up and down makes the emulated CPU >>> go faster and slower. I have seen code using simple counters as delays >>> but I assume that if you want precision you use the Kw11. >>> >>> With regards device responses I have found that going ’too fast’ >>> upsets code. If they do something that triggers an interrupt (set ‘go’ >>> for >>> example) and the interrupt arrives too soon (like before the next >>> instruction) they get surprised and can misbehave (you could argue >>> that’s a bug, but that’s irrelevant). So always wait a few beats. But >>> I assume there is no reason to try to precisely emulate the timing of >>> , say, a disk drive. (The early handbooks state how awesome the async >>> nature of the IO subsystem is cos you can swap out old for new and >>> things just go faster). >>> >>> >>> _______________________________________________ >>> Simh mailing list >>> Simh@trailing-edge.com >>> http://mailman.trailing-edge.com/mailman/listinfo/simh >>> >> >
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