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

[Johnny Billquist <bqt%softjar.se@localhost>]

On 2023-12-26 04:36, Mouse wrote:
> > Are you sure it is supposed to be edge triggered?
>
> No.  I did not record why I did that; to tbe best of my current memory,
> I implemented simple level-triggered interrupts, with DONE&IE as the
> interrupt condition, and it didn't work right.  (Note that, unless I've
> totally misread the code, simh does the equivalent of edge-triggered as
> well.)

I just checked simh, and it appears to clear the interrupt pending as 
soon as the data register is read, which to me definitely means it's not 
edge triggered, but level triggered.

Basically, the code looks like this:

int32 rxdb_rd (void)
{
int32 t = tti_unit.buf;                                 /* char + error */

if (tti_csr & CSR_DONE) {                               /* Input pending 
? */
    tti_csr = tti_csr & ~CSR_DONE;                      /* clr done */
    tti_unit.buf = tti_unit.buf & 0377;                 /* clr errors */
    CLR_INT (TTI);
    sim_activate_after_abs (&tti_unit, tti_unit.wait);  /* check soon 
for more \
input */
    }
return t;
}



Note the CLR_INT (TTI); in there. Which will happen independent of if 
the CPU have picked up the interrupt or not. The code basically follows 
the documentation, which says that the DONE flags is cleared when you 
read out the data. And the interrupt request is a combination of DONE 
and IE. So at that point, the conditions for an interrupt goes away.

> > Tried to find some docs, but the KA630 manual I found don't
> > explicitly say one thing or the other.  Could you point to where
> > assumptions about edge interrupts exist in the code, or are defined
> > in some doc?
>
> No, because I don't have any such.  I would have been delighted to have
> found anything that precise about the SLU interrupt hardware.  I've had
> to experiment and see what works.  That's why I'm asking after someone
> who knows enough to give a precise enough description to write an
> emulator to.

The manual that I read was a bit fuzzy, but my reading would have 
suggested it's level triggered as well. But I don't think the wording 
was definite enough to say beyond doubt. But the fact that simh also 
seems to think it's level triggered makes me feel more confident. After 
all, I would assume Bob knows these details pretty well. :-)

  Johnny

--
Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt%softjar.se@localhost             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol