Re: A500 [was : AmigaOne X5000]

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Tue, 21 Mar 2017, goon wrote:

> Hello,
> 
> On Thu, Mar 16, 2017 at 11:38:10AM -0400, Michael wrote:
> > Hello,
> > 
> > On Thu, 16 Mar 2017 03:49:19 +0100
> > goon <goon%yellowcouch.org@localhost> wrote:
> > > > Maybe you meant ACube's AmigaOne 500? :)  
> > > 
> > > No, it's for the A500 from 87 :-) There's just support ending in obsd 3.2
> > > for the A1200 and up.
> > 
> > Without an MMU? IIRC we already support A500 with a suitable CPU upgrade.
> > 
> 
> I read some history sites about the A500, I have on with 1Mb RAM. The thing is 
> I downloaded srcsys and am looking at the code but it is somewhat unclear to me
> where the differences lie in between the A500 and up until A2000 as these are
> newer supported machines.
> 
> Do you know where to find good datasheets for it ? The kernel can probably
> be improved by smaller memory footprints FWIW. 

You can take a quick look at wikipedia for the overview.

Basically, an A500 and A2000 are pretty much the same.  The A2000 had 
512KB chip RAM and 512KB of fast RAM.  Your A500 probably has 1MB of chip 
RAM.  Otherwise, the A2000 is in a case with expansion slots and a 
separate keyboard.

You can't really run NetBSD on those machines.  First of all, if you look 
at the compressed NetBSD 7.1 kernel for amiga over here:

ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-7.1/amiga/binary/kernel/netbsd-INSTALL.gz
 
it's already 1.8MB so you just don't have enough memory.

Secondly, as mentioned before, it has a Motorolla 68000 processor, which 
lacks an MMU, any way to attach an external MMU, or the ability to restart 
an instruction that accesses memory.  The NetBSD UBC (buffer cache) design 
is highly reliant on page faults to function properly.  

The first Amiga capable of running NetBSD is the A2500, which is 
essentially an A2000 with a 68020 with a 688851 MMU or 68030 (with built 
in MMU) accellerator card installed and 4MB of 32-bit RAM.  And a hard 
drive.

So unless you plan to pretty much completely rewrite the OS, you first 
need to upgrade the CPU.  You need either a 68020 + 68851, 68030, 68040, 
or 68060.  You will also need some more RAM.  Oh, and a hard drive would 
also be good since you won't have enough space to hold a decent root 
filesystem on 720KB floppy disks.

Eduardo