[Simh] Two questions

[Tim Riker]

Gregg C Levine wrote:
> Hello!
> First Question:
> I have TMPFS configured and probably working on my freshly activated and
> running Linux system. SimH is also setup to run there. Now the question: How
> would I go about informing the PDP-11 or VAX simulator that there is a
> location on my physical system called <name> and that it uses TMPFS and that
> it can use it as a virtual disk image up to about 10M. (Meg)

Most Linux distros mount tmpfs on /dev/shm and allow all users write 
access with the sticky bit set like /tmp. tmpfs is is primarily ram 
based but will swap pages to disk like process memory.

The kernel by default sets the max size of tmpfs to half of ram. This is 
very conservative. I often set the size up to all of RAM plus all of 
swap as tmpfs will swap to disk. Now that's a bit aggresive on the other 
end as you'll be in trouble if you really fill that up. You won't have 
any space left for processes. :)

A better size choice would be someplace in the middle, perhaps half or 
ram plus half of swap? I would just change the size of /dev/shm and NOT 
mount another tmpfs mount someplace else. Something like:

mount -o remount,size=3G /dev/shm

Many distros have boot settings someplace to change this. For Debian 
it's the setting SHM_SIZE in /etc/default/tmpfs, for SuSE it's 
SHMFS_SIZE in /etc/sysconfig/kernel for example.

I'm not sure how you would tell simh pdp-11 about it. You could copy 
disk images over there and then tell simh to use those, but then you 
need to be sure to copy any disk images back that you wish to preserve 
changes as the tmpfs files disappear on the next reboot.

I'll leave the other ?s to those with more pdp-11 knowledge.
-- 
Tim Riker - http://Rikers.org/ - TimR at Debian.org
Embedded Linux Technologist - http://eLinux.org/
BZFlag maintainer - http://BZFlag.org/ - for fun!