Amiga and MMU equipped Accelerators

Quote:

---

Originally Posted by rkauer

It is the Motorola EC030 at 50MHz you got here.

No MMU, but still is a 50MHz 030!

---

Sorry for hijacking the thread, but what actual difference does an MMU make to an Amiga? I didn't think AmigaOS had any form of memory protection.

I guess if you wanted to run 68k Linux, you'd need one, but if you're running Workbench...?

relockick, backkick and other kickstart to fastmem type tools use mmu to trap and redirect memory accessing.

Quote:

---

Originally Posted by arnljot

relockick, backkick and other kickstart to fastmem type tools use mmu to trap and redirect memory accessing.

---

They don't require it. Relokick works for me on bog-standard 68000 Amigas. Maybe there's a performance boost if an MMU is present?

blizzkick uses it
http://aminet.net/package/util/boot/BlizKick

also developer tools can take advantage from an mmu

Quote:

---

Originally Posted by arnljot

relockick, backkick and other kickstart to fastmem type tools use mmu to trap and redirect memory accessing.

---

Also you need a working MMU to run OS3.5 and 3.9. Witohut one the Amiga will have to use other nasty tricks to load the ROM updates.

Just directing the flow of traffic from this thread =)

Quote:

---

Originally Posted by rkauer

Quote:

---

Originally Posted by arnljot

relockick, backkick and other kickstart to fastmem type tools use mmu to trap and redirect memory accessing.

---

Also you need a working MMU to run OS3.5 and 3.9. Witohut one the Amiga will have to use other nasty tricks to load the ROM updates.

---

Still, those nasty tricks seem to do the job. My A1200 with an EC030 runs OS 3.5 very nicely indeed. :)

So what does an MMU do?


well my fellow forum chummy Alphonsus from eab states it very well -

Quote:

---

Originally Posted by alphonsus

The MMU converts one set of memory addresses to another, usually on a program by program basis.

Say program A wants 2Mb. It gets told it has addresses x to y.

The MMU can map that address range to wherever it wants to in the address space, including to hard disk (hence needing the MMU to run virtual memory properly).

Program B can also be given memory including addresses x to y, because the MMU redirects those addresses somewhere else in he address space.

Amigas never needed an MMU, but it is needed to run virtual memory, memory protection (fewer crashes) and most versions of linux.

---

A common thought is that the blizzard accelerators use the mmu to maprom, this is not the case - infact its the memory mapping logic that does the magic.

Quote:

---

Originally Posted by Toni Wilen

MMU was was usually only used for non-blizzard softkicking (A3000 for example required it) and debugging. Amiga virtual memory was a toy because there is no OS-level support.

---

So what programs actually used the MMU ?


Enforcer
Enforcer is an advanced debugging tool for Amiga computer systems equiped with a 68020/68851, 68030, 68040, or 68060 CPU.
It uses the MMU to help detect stray pointers and access to invalid memory.


Gigamem

Gigamem allows Amiga owners to use hard drive space as RAM.
Other than an MMU Gigamem requires some free hard drive space - (essentailly using this as a paged swap-file).

This means you can images and projects that are too big for your current memory setup. So instead of needing additional RAM to handle one or two projects, you can use Gigamem and used Harddisk space.


Fusion and Shape shifter emulators

These can make use of the MMU, although they are slower when using it.


Amix or NetBSD

Essentially carients of linux, as such run protected memory environments.

I believe there's one essential reason for having an MMU if you're a developer on the amiga, and that's Enforcer. It protects your machine (and sanity) from your own stupidity...

Gigamem is a nice idea well implemented, but is not really useful due to the speed. You need to be truly desperate to use it...

Quote:

---

Originally Posted by chiark

..
Gigamem is a nice idea well implemented, but is not really useful due to the speed. You need to be truly desperate to use it...

---

Or on Fast SCSI 3 via a Cyberstorm Mk3 / Cyberstom PPC

Still i have some hope that an 060@66 with FastSCSI2 would cope nicely with Gigame.... although to be fair... trying to find a project that requires more than 128MB of Ram on an Amiga is a little hard....