[Simh] something strange with simulated RK05 drive ?

[Johnny Billquist]

On 2020-02-12 01:49, Paul Koning wrote:
> 
> 
>> On Feb 11, 2020, at 7:37 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> On 2020-02-12 01:24, Paul Koning wrote:
>>> There is no such thing as "format", in the sense of writing sector headers, on an RK05.
>>
>> Uh... Yes there is. I happen to have written a formatting program myself on a PDP-8 for the RK05. It can definitely write the sector headers.
> 
> Oops.  You're right, I misremembered.

Once in a while, I do get my facts straight... More often than not, I am 
in error, though... :-)

>>> I don't think Henk was talking about SIMH having a problem, though I got a bit confused.  The question was about the fact that the fault light was coming on. My answer is: don't implement that light, there is no condition in the emulated drive that matches what that light does in the real drive.
>>
>> I think Henk was also reflecting on that the error condition in simh was triggered by the cylinder address error, and this is what he was using as the source for his error light.
>>
>> If I understood it right, Henk didn't implement the logic to trigger the error state. He's merely extracting the information in order to display it on the RK05 panel. And the light went on, and that led us here...
>> But I might have missed the whole point...
> 
> 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.

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...

   Johnny

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