[Simh] Simulator lockup when booting RSX-11/M+ V4.6 BL87 baseline system disk with insufficient memory

[Johnny Billquist]

On 2014-01-22 08:16, Christian Gauger-Cosgrove wrote:
> Hello:
>
> I've noticed an odd issue. When booting the aforementioned baseline
> RSX-11/M+ disk, with 256K of memory, RSX-11 doesn't have enough RAM to
> work when it tries to run the startup script. This happens as the
> system doesn't have enough memory to allocate a checkpoint space; so
> RSX-11 gets stuck in an infinite loop repeating:
> <TIME>  *** GEN    Checkpoint space allocation failure
> Where <TIME> is the current time in HH:MM:SS format. The CPU is
> working, as you can see the time field counting properly. However, the
> simulator completely locks up otherwise; you can't Ctrl+E to the sim>
> prompt, you can't Ctrl+C or Ctrl+Z the program within RSX-11 itself.

Sounds like a problem in simh, yes.

But just to clarify one thing with RSX here. The problem is not about 
not having enough memory to allocate a checkpoint space. What the error 
means is that RSX do not have a checkpoint space.
Checkpoint space is the RSX term for disk space used to swap out running 
tasks to, in order to free memory.

But yes, the basic problem is that you have too little memory. The 
startup script will setup a checkpoint space for you, but you don't even 
make it that far... The basic tasks activated at startup is already 
requiring more memory than you have.

	Johnny