[Simh] Simh Digest, Vol 117, Issue 4

[Johnny Billquist]

On 2013-09-06 17:55, Jon Elson wrote:
>
>> Date: Thu, 05 Sep 2013 12:02:04 +0200
>> From: Johnny Billquist <bqt at softjar.se>
>> To: simh at trailing-edge.com
>> Subject: Re: [Simh] single cycle stepping for pdp11
>> Message-ID: <5228569C.3060307 at softjar.se>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> On 2013-09-05 07:15, Mark Pizzolato - Info Comm wrote:
>>> On Wednesday, September 04, 2013 at 10:08 PM, Doug Snyder wrote:
>>>> it appears that simh supports single instruction stepping, but not
>>>> single cycle stepping for the pdp11.
>>>
>>> Hi Doug,
>>>
>>> The core behaviors of the simh simulators are built around the
>>> execution of instructions.  This is the level which things are
>>> simulated at.
>>>
>>> What problem are you trying to solve or deal with your request to be
>>> concerned about clock cycles?
>>
>> And even further - single cycle stepping will mean different things on
>> different models of the PDP-11. Or rather, different models do
>> different amounts of work in a single cycle.
>>
> I worked for years on PDP-11s, and never heard of this single cycle
> stepping.
> I can imagine there might be a jumper on one of the boards that enables
> this
> for customer engineer's debugging, but as far as I know you only got single
> complete instruction stepping with the halt switch.  I worked with the
> 11/20, 11/34, 11/45 and even the CalData emulator.

I would have expected the 11/45 to be similar to the 11/70 in this case.
The 11/70 have one switch on the front panel labelled "S INST/S BUS 
CYCLE". If you are halted, and pull the CONT switch, with HALT enabled, 
it will single step. Either one instruction, or one bus cycle, depending 
on this switch.

	Johnny