Re: KA630: how does console I/O actually work?

Yeah. I was trying to read through and understand the output side as 
well, and feeling that it's weird. I need to read and think some more on 
this. Also trying to read the docs and not seeing anything about 
interrupts not happening again, so I'm at a loss how this is supposed to 
work right now.

   Johnny

On 2023-12-26 15:33, Mouse wrote:
>>> I have now switched back to a pure DONE&IE (RX) or RDY&IE (TX)
>>> criterion for SLU interrupts.  I find that the ROM selftest is happy
>>> but that NetBSD falls into a livelock taking an apparently-endless
>>> stream of TX interrupts.
> 
>>> I don't yet know more.
> 
> I think NetBSD is depending on taking the interrupt being enough to
> clear the interrupt.  gencntint() just clears TS_BUSY and calls
> gencnstart().  When there is no character available, gencnstart()
> checks TS_ASLEEP and, if set, clears it and calls wakeup(), then
> unconditionally calls selwakeup(), and...that's it.  Nowhere does it do
> anything that would clear either RDY or IE.
> 
> For this code to have ever worked, the interrupt must act
> edge-triggered in the sense that taking the interrupt causes it to not
> recur unless/until its triggering condition arises again.
> 
> And, indeed, that's what I see in simh's code.  You wrote of int_req[]
> being the analog of an interrupt request signal; consider get_vector()
> in vax6530_io.c, which, without clearing any DONE/RDY or IE bits,
> clears the relevant bit in int_req[] when computing the vector for an
> interrupt.  This behaviour feels very edge-triggered-y to me.
> 
> Or, at least, that's what I see as of commit b41d10f189 in what appears
> to have been cloned from git://github.com/simh/simh, which of course I
> can't git pull from these days.  But git blame says the relevant code
> was last changed 2012 (most of get_vector) or 2015 (some of it).  (That
> commit is timestamped 2017-03-07.)
> 
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