[Simh] something strange with simulated RK05 drive ?

[Paul Koning]

> On Feb 11, 2020, at 8:02 PM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> On 2020-02-12 01:49, Paul Koning wrote:
>>> ...
>> There is no fault light handling that I can see in SIMH.  The way I read Henk's comment is that he observed from debug messages added to pdp11_rk.c that RT11 FORMAT was passing an out of bounds cylinder number.  FWIW, I see RSTS-11 DSKINT format code stopping at cylinder 202, as expected.
> 
> Ok. You obviously looked deeper into it than I did. I have not actually checked the simh code here.
> 
> But I did now... And I don't agree with you. simh is setting an error state if you ask for a too high cylinder. And the error is exactly what Henk described. RKER_NXC is set.

Yes, in the status register.  What I said is that there is no "FAULT" in SIMH.

> You are misunderstanding what Henk wrote.
> 
> However, with that said, Henk have misunderstood the system. It is important to understand that the disk drive and the controller are two separate entities. The fault light is only about error conditions on the disk drive, not the controller.
> Out of cylinder errors are caught by the controller and never even gets to the disk drive, so there is nothing that the disk drive will indicate for this.
> 
> Henk, you need to understand how these systems work a little better. :-)
> 
>> I'm not sure why one would format an emulated RK05, assuming that it only simulates the data portion of the sectors and not the header word.
> 
> Oh, I agree that it's pretty much a NOP really.
> But if you have the system, and a command in there, you can bet that someone is going to run it. And at least the system should pretend it did the "right" thing...

It gets a bit tricky if you actually want to emulate the FORMAT bit.  While for writes it can just be ignored, there is the read operation with format set, which is documented as returning one word per sector, the header word.  I haven't seen that in use, perhaps it is found in diagnostics.  Does anyone know?

	paul