PDP-11/40 - DMA and Bus Reset Behaviour

[Ashlin Inwood]

I have an 11/40 I am only working on, I recently installed a unibone and have it working.

I have found some odd behaviour I am not sure about.

When I have the PDP-11 running light chaser or any other program that exercises the RESET instruction, I find that unibone DMA transactions do not operate correctly. Somtimes examine (e 1000) will timeout, and other times it will get a value from memory from the previous value on the bus rather than the requested value. 

Is this behaviour an indication of a fault or just the unibone not handling the bus reset all that well? A regular endless loop programming works fine with DMA.

Thank you

[Wolfgang Schmitz]

Hi Ashlin,

to 99% I would say, that UNIBONE works correct.

I know that you are able to microstep.

Did you do microstepping around the RESET command, to see what happens?

Maybe that isn't even helpful, if a bus timeout is in progress as well....

I am planning a post of my experiences on VCFed, what do you think about that?

I'm a little short of time right now, but i wanted to let you know that i work on likely the same issues!

Wolfgang 

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