FPGA for dummies

[JimS]

How does it sound like that? I've said on more than one occassion that I like both. It's obvious from my question that I like both.
 
Only by saying that software is emulation but fpga is not emulation does it sound like prejudice.

My only concern is to recognize the different technology in the two approaches. Software emulation is different from FPGA implementation. Has nothing to do with anything other than that. They are both ways to do an Amiga, or other things.  

Suppose for example we were talking about music players... You can have a casette player and a CD player. Both do the same thing, but in fundamentally different ways.

[psxphill]

Suppose for example we were talking about music players... You can have a casette player and a CD player. Both do the same thing, but in fundamentally different ways.

Using the FPGA isn't emulation argument then the CD player doesn't play music as it is converted from analogue to digital and then back to analogue, while the tape stores an analogue wave.
 
In reality they are both lossy audio storage & reproduction systems, but the loss is in different areas.
 
Using hardware or software for emulation is still emulation, you need to differentiate in another way.
 
A static recompiling emulator is fundamentally different to an interpreting emulator, yet neither is "not an emulator".

[freqmax]

One  of the methods can adhere to the timing specification of the original design.

[bloodline]

One  of the methods can adhere to the timing specification of the original design.

Not true, I could program a microcontroller to respond to signals correctly to replicate the functionality of an ASIC (in fact I have used an ATMega328 in place of some old custom chip before). As long as it meets the timing as documented it will work.

[freqmax]

I did say one of the methods, I didn't say the other didn't. You assumed.
A processor unless given an uneconomical performance will have a low probability to adhere to the clock cycle timing of the orignal design.

[psxphill]

I did say one of the methods, I didn't say the other didn't. You assumed.
A processor unless given an uneconomical performance will have a low probability to adhere to the clock cycle timing of the orignal design.

Depends on the circuit & the processor. There are circuits that are too fast to put into an fpga.

[mikej]

In the 6502 case it is mostly predictable, in other chips there may be other entropy that makes it harder to predict. As soon as you have to work out if they are likely to float in one direction or the other & adjust the VHDL accordingly, then you cannot be using the original circuit 1:1.

Well, you are actually - you are more accurately modelling the original circuit. However, any two (original) devices will probably produce different results, so which is correct?

The side effects of an NMOS circuit are going to be different to that of a CMOS circuit. Even an FPGA & ASIC running from the same VHDL don't necessarily behave the same way due to clock skew.

um, yes they would. All devices have clock skew correct, but as long a skew + logic delay + flop set up < clock period they will behave identically. Always.

 

Something like the Z80 R register, which is a read/write random register. However it's not really random because it's the ram refresh register. Loading it repeatedly can cause your memory to not be refreshed, so bits randomly drop out if the memory is not read by the CPU. I'd love to see how an accurate FPGA simulation of that would work.

The register you talk about is not random in the slightest, it is a counter used to generate the address for DRAM refresh. Loading it repeatedly would cause corrupted memory, but I guarantee no two systems would see the same corruption pattern. An FPGA simulation using the same memory would behave in the same way. Normally we make our lives easier and use memory controllers which work, or SRAM - so you wouldn't have to worry about this particular problem.

[mikej]

Depends on the circuit & the processor. There are circuits that are too fast to put into an fpga.

Name one?

[JimS]

Using the FPGA isn't emulation argument then the CD player doesn't play music as it is converted from analogue to digital and then back to analogue, while the tape stores an analogue wave.
 
In reality they are both lossy audio storage & reproduction systems, but the loss is in different areas.
 

You make my point for me. ;-)

[amiga4ever]

if it wasn't made 20+ years ago, it's not a "real" classic Amiga. real, for many classic Amiga enthusiasts, is defined by more than logic gate responses on a microchip. it also involves knowing that the system you are using was physically present with you in the past. it's tangible nostalgia, something fpgas recreate very poorly. in that respect alone, fpgas certainly are a poor simulation/substitute for a real amiga.

[xyzzy]

If you performed a test, with FPGA and real hardware hidden behind a wall or something, and people could not tell the difference the two, then that's good enough for me.

[amiga4ever]

for a lot of people, they WOULD be able to tell the difference.

it's interesting to note:  on the Amiga and c64 demoscene, i can cite a few examples of new demos (created after fpga blueprints for these systems) which push REAL hardware to the limit yet run fine on real machines. yet, because they do not play nicely with documented hardware timings and such - the code breaks fpga "hardware" and software emulatrs.

it may not be strictly "correct" terminology to call recreations of chips on fpgas an emulation, but that is their effective result.

i could program a fairly decent rule based inference system to replace the knowledge response of my local GP. but i wouldn't like to bank on it to diagnose anything out-of-the-ordinary and uncommon. not before reflashing/programming it with updated knowledge from a REAL doctor.

superficial familiar response != real

[persia]

@xyzzy

And the same could be said for UAE.

[NorthWay]

"Is AGA a "proper Amiga" chipset?"
Perhaps it's a partial replica? Doesn't matter, because it was designed and made by the makers of Amiga.

Was it? How many of the original Los Gatos crew were left at C= to do AGA?

And yes, it matters. Either AGA is a proper Amiga chipset or it isn't. Make up your mind.

Why does it matter? Because the VHDL/Verilog design can probably be scrunched from someones security backup (if exonerated). That gives you the _original_ AGA design. In pure electronic form. Ready to be pushed into silicon again in 2011 (make that 2012).
But I guess according to some funny "rules" it wont fly unless it is done in the same fab process as the original was? And certainly not implemented with an FPGA or two.

(I guess Jens Schoenfeld is a heretic who will be first up against the wall for having pulled chips one by one out of an A1000 and replaced them with an FPGA.)

[NorthWay]

The AGA chips that commodore designed and had manufactured are "proper". Anything you design and manufacture are not the same.

I'll join you in playing your game of semantics:

If C= was still alive today (and filthy rich) and pulled out their original VHDL/Verilog for AGA to make a "20-years celebratory model" 4000 and had new chips manufactured by one of today's chip foundries in a current fab, would that be a proper Amiga?
If they made an internal test first to check their tools and used FPGAs to implement it, would that be a proper Amiga?

If I had a backup tape passed over from a friend of a friend with the original design and had it implemented in the same fab as used in 1990(91?) would that be a proper Amiga?
If yes, would it be if implemented in a current fab?
If yes, what about if I used FPGAs for it?

If you attend a faire with Jens Schoenfeld showing two A1000s and he tells you "one of these have had the custom chipset removed and replaced with FPGAs" and you can't tell the difference (assuming you have all the sw in the world to bring along to test), which one is a real Amiga?

[freqmax]

Machines that adhere to the same electrical specification as the "original" is real.

The missing masks, and original code just shows how bad proprietary designs are for long term usage. But that's the way it is, like it or not. Someone could scan the orignal chips (don't throw them!). But such process is still hard. So the method that remains is reverse engineering.

Does anyone know how the orignal designs were managed?, I know 6502 was done with manual methods like pen and papper, OCS used logic chips and wire-wrap. But somewhere after that they ought to migrated into some electronic design system.