Accelerator Cards

[sim085]

From the amiga memory layout there are some things I can understand and some which I cannot (surprise surprise :-))

Always talking from the A500+ perspective (since that is the only machine I have);

'2MB chipram' refers to the 1MB chipram which comes on the motherboard and the 1MB chipram which can be added in the trap door slot.

'8MB Zorro2 autoconfig space' refers to the ram that can be added through for example a side slot expansion such as the GVP A500HD8+ which takes 8MB and the A590 which takes only 2MB if I remember correctly.

'512KB slow ram on A500' I cannot understand ... isnt this the ram that comes on the motherboard and therefore part of the chipram?

'3.5+GB free for use by 32bit accelerators' refers to the memory space that can be on an accelerator card.

Are the above correct; as I said the thing that confused me the most is that 512KB.

The memory table is very helpful to understand the concept. Strange to see that memory wise an A500 can be better equipped (if wanted) then an A4000 :-P

[countzero]

yes. you got it right. The 512k on the A500 is chip RAM. However, the 512k you put on the trapdoor slot of a regular A500 (not A500+) is slow RAM. There's yet another address space just allocated for A500 trapdoor slot which is 1.8 mb I believe (called ranger memory, or something like that). Normal A500 maps trapdoor memory there. This is neither chip nor fast ram though. It is as slow as chip ram, but not accessible by the chipset, therefore called slow ram.

[darksun9210]

sorry, i should have made that bit clearer  :-)

the A500+ has one meg on the mainboard, and the 2nd meg in the trapdoor is mapped to the addresses right after it, so you have 2meg continuous chipram, like all machines after it. A600,A1200,A3000,A4000 etc.

The A500 (non plus) only had 512k chip ram on the motherboard, the area where the extra 1.5Mb of the A500plus's ram was mapped as "reserved", and the 0.5MB  trapdoor expansion was mapped to the "slow ram" area.

the 3.5GB+ free refers to the available address space that the CPU can get to, _if_ the memory controller can understand that much ram. a-la Viper handing "only" 128MB, but i recon it could do more if it had more simm slots. :-D

-edit-

i guess the "ranger memory" is the address space that hasn't been used, but the trouble with this, and "slow" ram, is that it is "fast" ram in that only the CPU can access it, but it is slow in as much as it has to go across the chipram bus to get to it. so ends up having to ask the custom chips for permission to get to this "ranger mem" and hence slower than true fast ram on the side port or accelerator, as that is controlled by the CPU for the CPU.

[sim085]

Ok thanks a lot to everyone for all the answers. I will need some time to understand all this but things are much more clear now

Something else completely different now; What determines the maximum processor that can be used on an Amiga. What I mean is that for the A500 you only find processor up to 040 while for the A4000 you find processor up to 060 (I do not know if more) and even PPC. What determines what type of processor can be used.

Also what is the use to have a processor running at 50Mhz if the socket to which it is connected has only a data transfer of 7.14 MHz (if I understand the specs here correctly: http://amiga.resource.cx/mod/a500.html).

[countzero]

there are no fixed rules about what kind of processor can be used with an amiga. anything can be used as long as you interact them with proper bus handling. The reason why there are no 060 accelerators for A500 is simply because no one made them, because A500 being the low end of the amiga line, people not being able to afford even and a1200 most probably will never buy a 060 board for a500.

also 68000 bus (A500) and 68020 (a1200) are different in that it is more easy for a1200 to interact with a 68040 bus I belive. But it is possible as there are 68060 boards for A2000, which is a 68000 bus. Theoratically, you can run a PPC accelerator on an A500 with Zorro2 bus expansion, blizzard 2060, PPC developer board.

[Piru]

@sim085

The operating system would tell the process what instruction to execute and where to store the result and the operating system would know the allowed memory space because of this small program you mentioned. is this right? or I am confusing things?

The memory resources are maintained by the OS (exec.library). At early startup phase the OS pinpoints the amount of chip (at address 0) and ranger memory (at address $c00000). Other memory (accelerators, Z3 etc) is added to the system by AutoConfig(TM) (expansion.library).

When program is loaded, the OS allocates memory from the memory pool for the program sections. The program execution begins at the beginning of the first section.

While running programs can also allocate memory memory dynamically using the exec.library functions. This memory is also obtained from the memory pool. Typically programs also free most of the memory they allocate, returning it to the memory pool.

When the program is finished the control returns to the OS. At this point the OS unloads the program sections, returning th memory occupied by them to the memory pool.

The CPU itself doesn't care what memory it accesses, it accesses exactly what the program tells it to. In case non-existing memory is accessed, several things can occur depending on the CPU and bus type. Older systems (typically 68000 to 68020) have undefined behaviour, the access might go unnoticed, might return random or mirrored content or it might totally screw the system. A3000, A4000, and expanded systems with 68030 to 68060 CPUs typically have more control. With these systems/CPUs accesses to non-existant memory generate an exception which the software can then handle. By default the program just gurus, but in some cases more advances things can be done: For example virtual memory (Gigamem, VMEM) or extra debugging (Enforcer, CyberGuard, muForce).

(This is a slight simplification, but I wanted to keep it understandable. I hope this helps clarify things.)

[sim085]

Yes but you need the Zorro2 bus expansion because the blizzard 2060 connector is for an A1200 and not for the A500 processor socket right? What I mean is that if (theoretically or fantasy speaking for some) you put an 060 an a board which can connect to the processor socket of an A500 then the processor would still work. or?

[countzero]

I was talking about something like this which gives an A2000 processor slot (Zorro2 is irrelevant), yes it should work.

[sim085]

countzero wrote:
I was talking about something like this which gives an A2000 processor slot (Zorro2 is irrelevant),

Yes I understood that; what I meant is that you need one of those to connect a blizard 2060 because the connector is different then the connector of an accelerator card for the A500.

countzero wrote:
yes it should work.

I do not want to push it but does this also apply for a PPC? I know you already said it should work in your previous post. However I was thinking that a PPC recieves instructions in a different way then an 680X0 processor. If so then only an OS which can send such instructions can work (example OS4.0) and I do not know how much you could fit that on an A500 with a PPC.

Again I must repeat that this is just hypothetical speaking. I am just trying to understand the concepts behind accelerator cards not actually thinking to build one since I have no electronics experience ... sorry for any one who was hopping for that ... maybe one day in the future ;-)

[countzero]

well maybe you should see for yourself ?

Amiga 2000 with PPC

An amiga 2000 is basicly an A500 with Zorro2 slots and buster. They have the same 68000 based bus. If it works on an A2000, it should work on an A500.

[sim085]

but how is it possible ... how can the same instructions used for the 680x0 processor also work on a PPC processor? I can understand between different 680x0 processors but not between completely different processors!

[countzero]

you misunderstand. The 68k code does not run on PPC. Only specifically compiled PPC code runs on PPC. The main OS runs on 68k. But some parts (computation heavy stuff like jpeg, mp3 decoding, etc) have special libraries which run on the PPC cpu. This is the case for OS 3.9 (an 68k OS)

OS 4.0 for classics is different though. It runs totally on PPC cpu. 68k programs also run on an 68k emulator on PPC CPU.

[sim085]

aaaa ... i checked the video again and he puts the 68060 processor back on the PowerUp Dev board...

This is such an interesting subject and I personally could keep asking one question after the other :-)

Thanks for all the answers ... there is much to think about after this thread :-)

 

[Piru]

@sim085

Yes but you need the Zorro2 bus expansion because the blizzard 2060 connector is for an A1200 and not for the A500 processor socket right?

Blizzard 20x0 connects to the A2000 CPU socket (CPU Fast Slot). A500 doesn't have it, although some rare expansion units give it.

http://www.amiga-hardware.com/showhardware.cgi?HARDID=174

But seriously: While A500 with PPC is in theory possible it really isn't worth the trouble. :-)

[sim085]

Piru wrote:
But seriously: While A500 with PPC is in theory possible it really isn't worth the trouble. :-)

I understand that and I do not have plans to put a PPC into my A500+ :-) I am just trying to figure out what the limitations are.

However one can imagine (or a better word is 'fantasies') an accelerator card which can emulate different processors ...

You can have a board with any type of processor on top of it and some extra ram as well. the processor would actually run only a single program which would be an emulator. The instructions received from the Operating System would be translated and then executed. Like this you can have a single board which can be configured as a Viper, Derringer, Blizzard, etc ...

I know some will say why not use WinUAE and get it done with, but would something like the above be possible?

[Zac67]

Blizzard 20x0 connects to the A2000 CPU socket (CPU Fast Slot). A500 doesn't have it, although some rare expansion units give it.

The A2000's CPU slot and the A500's expansion port are actually very much alike - something like a simplified Zorro II slot w/o AutoConfig.